8,153
edits
Changes
Created page with "Common sources of Caffeine. Caffeine is widely consumed by the general public and athletes, and moderate levels can improve athletic pe..."
[[File:Caffeine.jpg|right|thumb|500px|Common sources of Caffeine.]]
Caffeine is widely consumed by the general public and athletes, and moderate levels can improve athletic performance. Caffeine does not cause dehydration, but it can interfere with sleep. Caffeine in coffee does not seem as effective, so other sources should be used.
=Intro=
Man has been searching for ways of improving athletic performance since at least 400 BC, when the hearts of lion were believed to impart benefits<ref name="CaffLionHeart"/>. Today, caffeine can improve performance in endurance running, and three of every four elite athletes take caffeine when competing<ref name="CaffUse"/>. Caffeine is one of the most widely used drugs in the world<ref name="CaffWorld"/>, with average daily intakes worldwide of 70mg/day, but higher in the US (~200mg/day) and the UK (~400mg/day)<ref name="CaffDependence"/>. Caffeine has many effects on many different tissue types, directly and through its metabolites, as well as stimulating adrenaline release<ref name="CaffMetaAndPerf"/>.
=Performance =
Studies have shown caffeine can improve performance by ~2%<ref name="CaffMeta"/>. Though much greater improvements (~12%) have been shown in laboratory conditions, these are not likely to be seen in real world race conditions<ref name="CaffMeta"/>. That ~2% represents 3.5 minutes on a 3 hour marathon, nearly 5 minutes on a 4 hour marathon. For the 5K, that represents 25 seconds on a 21 minute 5K, or 18 seconds on a 15 minute 5K. Caffeine tends to benefit fitter individuals more<ref name="CaffMeta"/>. Caffeine may improve performance by reducing the [[Rating of Perceived Exertion|RPE]]<ref name="CafRPE"/> and muscle pain<ref name="CafMusclePain"/>.
==Green Tea and Performance==
There is relatively little research concerning the effect of tea on athletic performance. However, one study did show that the green tea extract increased fat burning and glucose tolerance during cycling at 60% [[VO2max|V̇O<sub>2</sub>max]] without affecting heart rate or overall energy consumption<ref name="Venables-2008"/>.
==Coffee and Performance==
When you take caffeine as coffee, it may not improve performance as it does when taken in other forms. One study showed that caffeine in coffee does not give a performance improvement where isolated caffeine does<ref name="CaffCoffee"/> and another showed no benefit from caffeinated coffee over decaffeinated coffee<ref name="CaffCoffeeButts25"/>. Some studies show a performance benefit from caffeinated coffee<ref name="CaffCoffeeWiles"/><ref name="CaffCoffeeCostill"/><ref name="CaffCoffeeCasal"/>, but did not compare with caffeine alone. This may be because coffee contains hundreds if not thousands of compounds besides caffeine<ref name="CaffMetaAndPerf"/><ref name="CafCoffeeCancer"/>. Some of these extra compounds of been shown to affect glucose metabolism<ref name="CafT2DMSysRevDam05"/>. It is been observed that decaffeinated coffee can reduce the absorption of glucose<ref name="CaffDecaffCoffeeGlucose"/>.
=How much?=
Most studies use 3-13mg/Kg, average 6mg, but within that dose range there was no obvious dose response<ref name="CaffMeta"/>. A smaller intake of 3 to 5 mg/kg dose before exercise and then 1 to 2 mg/kg intakes during prolonged exercise has been recommended<ref name="CaffMetaAndPerf"/>. Too much caffeine (9 mg/kg), especially for those that do not regularly take caffeine, can cause impairment, such as becoming talkative, giddy, and unable to perform simple tasks such as telling the time<ref name="CaffMetaAndPerf"/>. Low levels of exercise (30% [[VO2max|V̇O<sub>2</sub>max]]) seem to increase the metabolism of caffeine<ref name="CafModEx"/>, but higher intensities have no impact<ref name="CafExThermal"/>.
=Caffeine and Dehydration=
Caffeine does not impact performance in hot/humid conditions, nor act as a diuretic when running<ref name="CaffDiuretic"/>. Caffeine at 360mg is a diuretic at rest, but not at 180mg or less<ref name="CaffDiureticDose"/>. Caffeine does not cause long term dehydration<ref name="Caff11day"/>, and black tea has been shown to hydrate as well as water<ref name="CaffTea"/>. Caffeine does result in increased sodium excretion in the urine<ref name="CaffSodium"/>, but the significance of this unclear.
=Caffeine Habituation=
Surprisingly, there is no clear evidence that the performance benefits of caffeine vary with habitual caffeine usage<ref name="CaffMeta"/>. Caffeine impacts caffeine naive more at rest than those habituated to caffeine, but the difference is far less during exercise<ref name="CafHabituated"/>. Caffeine habituation has been shown to reduce the adrenaline response to caffeine, but most other responses remain similar <ref name="CafHabitAdren"/>. Animal studies have shown that some tissues adapt to long term use of caffeine but other tissues do not appear to change at all<ref name="CaffMetaAndPerf"/>.
=Caffeine and DOMS =
Caffeine has been shown to not only reduce the pain of [[Delayed Onset Muscle Soreness]] (DOMS)<ref name="CafPainDomsVol"/>, but also reduces the associated weakness<ref name="CafDOMSForce"/><ref name="CafDOMSMice1"/><ref name="CafDOMSMice2"/>. This reduction in weakness is important because although the soreness is delayed 24-72 hours after exercise, the muscle damage and resulting weakness happens within 30 minutes<ref name="DOMSTiming"/>.
=Caffeine Withdrawal=
Withdrawal from Caffeine generally produces a headache and fatigue, with some evidence of anxiety<ref name="CaffDependence"/>. Onset of withdrawal is typically 12-24 hours after the last intake, though occasionally as quickly as 3-6 hours, with symptoms after peaking 20-48 hours and lasting a week<ref name="CaffDependence"/>. Small amounts of caffeine can help with withdrawal.
[[File:Caffeine withdrawal and headache.jpg|none|thumb|300px|The onset and severity of headache with caffeine withdrawal.]]
[[File:Caffeine withdrawal and sleepy.jpg|none|thumb|300px|A similar chart of fatigue for caffeine withdrawal.]]
=Caffeine and Sleep=
Not surprisingly given it's a stimulant, caffeine interferes with [[Zeo Sleep Monitor|sleep]]. Taking 100mg caffeine just before bedtime significantly interferes with sleep<ref name="Landolt-1995"/>. More significantly, taking 200 mg early in the morning will also significantly interfere with sleep<ref name="Landolt-1995-2"/>. This suggests that caffeine should be taken as early in the day as is practical, and those with sleep problems should reduce caffeine or avoid it completely.
[[File:Caffeine and Sleep.jpg|none|thumb|300px|Caffeine concentrations measured in the saliva, with 200mg administered at 7:10am.]]
=Caffeine and Cramping=
There is no research around any possible link between caffeine and [[Cramps]], but there are a few anecdotal reports of a link between caffeine/coffee and [[Cramps]]<ref name="Stern2011"/><ref name="Dubowitz2011"/><ref name="Voermansvan Engelen2011"/>.
=Caffeine as a Pain killer=
Caffeine is frequently added to over-the-counter pain medication to boost its effectiveness; without caffeine 40% more pain medication is required to have the same results<ref name="CaffPainAdjuvant"/>. Caffeine adds slightly to the relief of surgical pain from Acetaminophen (Paracetamol)<ref name="CafParaPainSurgery"/> and caffeine can reduce headaches to an equivalent level as Acetaminophen (Paracetamol)<ref name="CafIsolationHeadache"/>. Caffeine reduces muscle pain during exercise in both those that habitually take caffeine and those that caffeine naïve<ref name="CafMusclePain"/>, though one study suggested this may only occur in hot conditions<ref name="CafMusclePainHeat"/>. As noted above, caffeine can reduce the pain of DOMS<ref name="CafPainDomsVol"/>.
=Caffeine at altitude=
The general recommendation to avoid caffeine at altitude does not seem to have a scientific basis. In fact, a number of the effects of caffeine have the potential to be beneficial at altitude<ref name="CafAltitude"/>
* As noted above, caffeine does not produce dehydration, and there is little evidence that dehydration contributes to altitude sickness.
* Caffeine tends to increase breathing, which may offset the depressed breathing seen at altitude.
* The risk of a brain or lung edema at altitude is a serious concern, and there is the possibility that caffeine may help by constricting blood vessels without restricting oxygenation.
* Caffeine may help alleviate the headache that is common with altitude sickness.
* The lassitude seen at altitude may be offset by caffeine, and the exercise performance improvements at altitude may be even greater than at sea level.
* While caffeine could reduce the altitude problems that prevent sleep, the stimulant nature of caffeine may offset these benefits.
Caffeine has a shorter duration of effect at high altitude, possibly due to increased blood flow to the liver, and withdrawal from caffeine would likely make altitude problems more severe<ref name="CafAltitude"/>.
=Glucose Absorption, Insulin Resistance and Glycemic index =
Caffeine changes the way glucose is absorbed, this effect is different before, during and after exercise.
==At Rest==
Caffeine reduces glucose absorption at rest<ref name="CaffGlucKel03"/><ref name="CaffGlucRestKei02"/><ref name="CaffGlucRestPizz98"/><ref name="CafGluRestInsResGrah01"/>. In tests on lean, obese, and Type 2 Diabetics, glucose absorption was impaired by caffeine, though exercise mitigated the reduction slightly in non-diabetics<ref name="CaffGlucObT2DMEx"/><ref name="CafGluRestObesePet04"/>.
==During Exercise==
Unlike the effect of caffeine on sedentary or resting individuals, caffeine increases the absorption, uptake and metabolism of glucose during exercise<ref name="CaffGlucExcYeo05"/><ref name="CaffGlucExcNieu99"/>. Caffeine taken during exercise does not change [[Glycogen]] replenishment post-exercise<ref name="CafGluExGlycBatt03"/>, but caffeine taken with carbohydrate after exercise increased [[Glycogen]] replenishment and insulin levels compared with just carbohydrate<ref name="CaffPostExcGlyc"/><ref name="CafGluExGlycPed07"/>. One hypothesis for this difference is that caffeine reduces the effect of insulin, and non-insulin dependent glucose pathways predominate during exercise<ref name="CafGluExGlycBatt03"/>. Caffeine taken 2 hours after exercise impairs glucose absorption, but to a lesser extent than in a completely rested state<ref name="CafGluExNonExhThon02"/>.
=Sources of Caffeine=
There are various sources of caffeine that are sometimes used by athletes.
==Coffee==
While coffee is a very common source of caffeine, there is evidence that caffeine taken in coffee is not as effective as other forms (see above for details). Also, coffee may cause [[Running and Stomach Problems|Stomach Problems]] and [[Running and Lower GI Problems|Lower GI Problems]] in some individuals. Typical brewed coffee contains 100-150mg per cup<ref name="Bunker-1979"/> which compounds the problem of using coffee in sports. I would recommend using other sources of caffeine before or during runs.
==Tea==
[[File:Caffeine Tea Brewing Time.jpg|right|thumb|200px|Brewing time and levels of Caffeine (CF), the catechins epigallocatechin gallate (EGCG), epicatechin gallate (ECG), epigallocatechin (EGC) and epicatechin (EC)<ref name="ShishikuraKhokhar2005"/>.]
It is claimed that tea is the second most popular drink after water<ref name="Macfarlane"/>, but it does not appear to be commonly used by athletes. Because the level of caffeine can vary dramatically with different types of tea, and different brewing methods, it is difficult to know how much caffeine is in a particular drink of tea. Generally black tea has more than oolong tea which has more than green tea<ref name="Lin-2003"/>. Typically black tea contains 28 to 46mg of Caffeine<ref name="Bunker-1979"/>. This unpredictability makes tea a problematic source of caffeine, though using the same tea and brewing for the same time will give reproducible levels, but you won't know the absolute caffeine intake.
==Gels ($2-8/100mg)==
Gels are available with and without caffeine, and the caffeinated variety normally has 25mg, though some go as high as 100mg. The higher caffeine concentrations often include a coffee extract, which may limit the benefits. Given that gels typically cost $1-2 per gel, the caffeine cost is $2-8/100mg. See [[Comparison of Energy Gels]] for more details.
==Soda==
The caffeine levels in soda vary widely, with some common values shown below.
{| class="wikitable"
!Soda!!Caffeine per 12oz<ref name="ChouBell2007"/>
|-
|Coca-Cola||33.9mg
|-
|Diet Coke ||46.3mg
|-
|Pepsi||38.9mg
|-
|Diet Pepsi||36.7mg
|-
|Dr Pepper|| 42.6mg
|-
|Diet Dr Pepper ||44.1mg
|-
|Mountain Dew ||54.8mg
|-
|Diet Mountain Dew||55.2mg
|-
|Vault Zero ||74mg
|-
|}
Typically soda makes a poor sports drink as it contains too much sugar, is too carbonated and additives like phosphoric acid can upset the digestive system. However, ultrarunners used to regularly use soda that had been left to go flat and then often diluted with water<ref name="CaffDeFizz"/>. This is something to practice in training before using during a race.
==Energy Drinks ==
There are many different types of energy drink available on the market today. Frequently they are a mixture of many different substances that are believed in some way to be stimulating. Energy drinks should be used with caution, as the substances they contain may not have been scientifically evaluated, especially in the combinations provided. Energy drinks often contain carbohydrate, but the specific types of carbohydrate and the concentration used may not be appropriate to athletic events. The caffeine content of energy drinks is often 200-300mg per can<ref name="CaffDatabase"/>, which is quite high, but lower than a Starbucks Venti brewed coffee which typically has 400+mg<ref name="CaffStarbucks"/>.
==Red Bull ($3-6/100mg)==
I've tried a few different energy drinks, and the only one I use now is Red Bull. Red Bull is only lightly carbonated, is not too sweet for my taste, and while the mixture of glucose and sucrose is not great for sports drink, it's better than many of the alternatives. I'm not sure if the added Taurine and B vitamins are beneficial, but the combination seems to work well for me. Red Bull contains about 80mg of caffeine per 8oz can<ref name="CaffRedBull"/>, which is slightly less than the equivalent volume of coffee.
==Energy Shots==
Energy shots are more convenient than energy drinks due to their small size and portability. However, they concentrated form can easily cause stomach upsets in addition to the problems noted in energy drinks above.
==Caffeine Tablets ($0.03/100mg)==
Caffeine tablets have the advantage of low-cost, predictable caffeine content, and portability. Compared with other sources of caffeine, these tablets are 1/100<sup>th</sup> the cost. I use [http://go.fellrnr.com?id=35454X937677&xs=1&url=http%3A%2F%2Fwww.amazon.com%2FNatrol-Caffeine-200mg-Tablets-100-Count%2Fdp%2FB000OPV118 Natrol] tables, which are 200mg per tablet. I cut them into halves using a [http://go.fellrnr.com?id=35454X937677&xs=1&url=http%3A%2F%2Fwww.amazon.com%2FApex-70068-Ultra-Pill-Splitter%2Fdp%2FB000EGKTGK Pill Cutter], then it's easy to bite off a smaller amount as needed. I carry these in my [[Portable Pharmacy]].
=Tea and Theanine=
Theanine is an amino acid found in tea, primarily green tea. Theanine calms the mind without inducing drowsiness, achieving a relaxed but alert mental state<ref name="CaffTheanNobr08"/>. Theanine has a number of benefits:
* It has been shown to improve and sustain long term attention<ref name="CaffTheanTopo09"/>, acting as a stimulant, even without caffeine<ref name="CaffTheanWimp07"/>.
* When combined with caffeine, theanine reduces distractions<ref name="CaffTheanBrya08"/>.
* Theanine reduces blood pressure<ref name="CaffTeaRelaxJune99"/> and can offset the rise in blood pressure that comes from caffeine<ref name="CaffTheanRoge08"/>.
* Three components of green tea (Catechins, Caffeine and Theanine) reduce obesity in mice<ref name="CaffTeaObesityZhen04"/>.
* Tea may help reduce dementia<ref name="CaffTeaDementSong12"/>, and tea improves learning in rats<ref name="CaffTeaRelaxJune99"/>.
* Theanine and cystine may help reduce the immune system depression of high intensity training<ref name="CaffTheanImune09"/><ref name="CaffTheanImune10"/>.
=Caffeine and health =
For most people, caffeine is generally taken as tea or coffee, to the bulk of the scientific evidence around the health impact of caffeine is based on these beverages.
==Tea ==
Both green and black tea contain similarly high levels of antioxidants<ref name="CaffTeaAntiOx"/>. Green tea contains high levels of [http://en.wikipedia.org/wiki/Epigallocatechin_gallate EGCG], which has been shown to inhibit cancer cell proliferation<ref name="CaffEGCGCancer"/><ref name="CaffEGCGCancerCerv"/>. This EGCG may help trigger natural cell death which in turn may help treat both obesity and osteoporosis<ref name="CaffEGCGObesity"/>. Green tea consumption has been linked to a reduction in upper GI cancers and green team may also help with lung, liver, prostate and breast cancers<ref name="CaffTeaCancer"/>.
==Coffee and Cancer==
Caffeine intake (coffee and other forms) is linked to lower rates of the most common type of skin cancer<ref name="CafCancerSong12"/> and coffee drinking is associated with a reduced risk of bladder, breast, buccal and pharyngeal, colorectal, endometrial, esophageal, hepatocellular, leukemic, pancreatic, and prostate cancers<ref name="CafCoffeeCancer"/>.
==Coffee and Type 2 Diabetes==
Coffee drinking is associated with a substantially lower risk of type 2 diabetes<ref name="CafT2DMSysRevDam05"/><ref name="CafCoffAoIMSala04"/>, including decaffeinated<ref name="CafCoffDam06"/>. However, coffee drinking is associated with a number of lifestyle risks, such as smoking, inactivity, and poor diet, and adjustments for these risks may overly strengthen the potential anti-diabetic benefits of coffee drinking<ref name="CafT2DMSysRevDam05"/>. There are a number of possible mechanisms behind the reduction in type II diabetes:
* In postmenopausal women, coffee increases the hormone [http://en.wikipedia.org/wiki/Sex_hormone-binding_globulin SHRB] that may account for the diabetes reduction <ref name="CafT2DM_SHBG"/>.
* Coffee (including decaffeinated) is correlated with reduced markers of insulin secretion, especially in obese and overweight women<ref name="CafCoffWu05"/>.
* One study found the T2DM risk was only reduced in tea and coffee drinkers who had previously lost weight<ref name="CafCoffGreen05"/>.
=Restrictions on Caffeine for Competition=
Caffeine was removed from the World Anti-Doping Agency (WADA) list in 2004; prior to that it was restricted at high levels based on urine concentration<ref name="CaffWADA"/>. It is still restricted by the NCAA at similarly high concentrations<ref name="CaffNCAA"/>. The level of caffeine intake required to exceed the NCAA threshold varies dramatically (x16) between individuals, and for a given individual at different times, with some people at risk of exceeding the permitted level on 3 cups of regular coffee per day and others able to take excessive levels<ref name="CaffUrineBrik91"/>. A study of caffeine showed that even 9mg/kg was less than the NCAA threshold for the test subjects<ref name="Graham-1991"/>, but another study showed that doses of 9mg or above could result in a positive test for some individuals<ref name="Pasman-1995"/>.
=Ethics of Caffeine=
At its most simplistic level, caffeine is permitted for use in competition, so if we consider "ethics" as simply "following the rules", then caffeine is ethical. If we look at the broader ethical implications of caffeine however, things become a little more nebulous. The World Anti-Doping Agency (WADA) may consider controlling a substance or method if it meets two of these three conditions:
# It has the potential to improve performance
# It has the potential to harm the health of the athlete
# It violates the "spirit of sport"
Clearly caffeine meets criteria \#1, but not \#2 (if anything, caffeine may be beneficial to health). So does the use of caffeine violate the spirit of the sport? Let's compare the use of caffeine with the use of carbohydrate:
* Both caffeine and carbohydrate have been shown to improve performance
* Neither caffeine nor carbohydrate are essential for life
* The vast majority of people routinely take caffeine, and nearly everybody takes carbohydrate
* There are few health risks with caffeine, and other than [[Fructose]], carbohydrate is generally considered safe
* While both caffeine and carbohydrate are found naturally in plants, it is common for them to be consumed in highly refined forms
* Athletes frequently consume caffeine and/or carbohydrate for the sole purpose of improving performance
* Any athlete that does not effectively use either caffeine or carbohydrate is at a distinct disadvantage
This comparison indicates to me that caffeine is not against the spirit of the sport, or unethical.
=Newborn babies and Caffeine =
Newborn babies may be subject to higher levels of caffeine from breast milk than one would expect. If we assume:
* A 3 Kg baby (6.6Lb)
* A milk intake of 500 to 900 ml/day<ref name="CaffBabyMilk"/>
* The nursing mother's caffeine intake of 200mg/day (one double shot espresso),
We get a resulting caffeine concentration in the milk of 4ug/ml to 8ug/ml<ref name="Stavchansky-"/>, which is a total caffeine intake of between 2mg to 13mg, or 0.6 to 4 mg/Kg body weight. The upper end of that level is quite high. However, the baby's half-life for caffeine is 60-100 hours, compared with an adult's 2-10 hour half-life, so the caffeine will build up over time. A 24 hour half live (which is easier to calculate) would result in about a 3mg to 26mg, which is 1 to 8 mg/Kg. I'm guessing that would result in the baby not sleeping well! Conversely, a baby whose mother takes caffeine during pregnancy and is then given formula milk may undergo caffeine withdrawal after birth<ref name="McGowan-1988"/>. Even if the mother breast feeds, the varying levels of caffeine may cause withdrawal symptoms<ref name="Martín-2007"/>. Also, caffeine has been shown to increase fetal heart rate<ref name="Buscicchio-2012"/>.
=References=
<references>
<ref name="Martín-2007">{{Cite journal | last1 = Martín | first1 = I. | last2 = López-Vílchez | first2 = MA. | last3 = Mur | first3 = A. | last4 = García-Algar | first4 = O. | last5 = Rossi | first5 = S. | last6 = Marchei | first6 = E. | last7 = Pichini | first7 = S. | title = Neonatal withdrawal syndrome after chronic maternal drinking of mate. | journal = Ther Drug Monit | volume = 29 | issue = 1 | pages = 127-9 | month = Feb | year = 2007 | doi = 10.1097/FTD.0b013e31803257ed | PMID = 17304161 }}</ref>
<ref name="McGowan-1988">{{Cite journal | last1 = McGowan | first1 = JD. | last2 = Altman | first2 = RE. | last3 = Kanto | first3 = WP. | title = Neonatal withdrawal symptoms after chronic maternal ingestion of caffeine. | journal = South Med J | volume = 81 | issue = 9 | pages = 1092-4 | month = Sep | year = 1988 | doi = | PMID = 3420441 }}</ref>
<ref name="Stavchansky-">{{Cite journal | last1 = Stavchansky | first1 = S. | last2 = Combs | first2 = A. | last3 = Sagraves | first3 = R. | last4 = Delgado | first4 = M. | last5 = Joshi | first5 = A. | title = Pharmacokinetics of caffeine in breast milk and plasma after single oral administration of caffeine to lactating mothers. | journal = Biopharm Drug Dispos | volume = 9 | issue = 3 | pages = 285-99 | month = | year = | doi = | PMID = 3395670 }}</ref>
<ref name="CaffBabyMilk">How much expressed milk will my baby need? : KellyMom http://www.kellymom.com/bf/pumping/milkcalc.html </ref>
<ref name="Landolt-1995-2">{{Cite journal | last1 = Landolt | first1 = HP. | last2 = Werth | first2 = E. | last3 = Borbély | first3 = AA. | last4 = Dijk | first4 = DJ. | title = Caffeine intake (200 mg) in the morning affects human sleep and EEG power spectra at night. | journal = Brain Res | volume = 675 | issue = 1-2 | pages = 67-74 | month = Mar | year = 1995 | doi = | PMID = 7796154 }}</ref>
<ref name="Landolt-1995">{{Cite journal | last1 = Landolt | first1 = HP. | last2 = Dijk | first2 = DJ. | last3 = Gaus | first3 = SE. | last4 = Borbély | first4 = AA. | title = Caffeine reduces low-frequency delta activity in the human sleep EEG. | journal = Neuropsychopharmacology | volume = 12 | issue = 3 | pages = 229-38 | month = May | year = 1995 | doi = 10.1016/0893-133X(94)00079-F | PMID = 7612156 }}</ref>
<ref name="CaffTeaCancer">Tea and cancer prevention: epidemiological stu... [Pharmacol Res. 2011] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/21419224 </ref>
<ref name="CaffTheanImune10">Cystine and Theanine Supplementation Restores High-Intensity... : The Journal of Strength & Conditioning Research http://journals.lww.com/nsca-jscr/Abstract/2010/03000/Cystine_and_Theanine_Supplementation_Restores.34.aspx </ref>
<ref name="CaffTheanImune09">Effects of oral supplementation wi... [Biosci Biotechnol Biochem. 2009] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/19352043 </ref>
<ref name="CaffUrineBrik91">Caffeine renal clearance and urine caffe... [Br J Clin Pharmacol. 1991] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/2049248 </ref>
<ref name="CaffNCAA">NCAA Banned Drug List - NCAA.org http://www.ncaa.org/wps/wcm/connect/public/NCAA/Health+and+Safety/Drug+Testing/Resources/NCAA+banned+drugs+list </ref>
<ref name="CaffWADA">2012 Prohibited List - World Anti-Doping Agency http://www.wada-ama.org/en/Resources/Q-and-A/2012-Prohibited-List/ </ref>
<ref name="CaffTeaRelaxJune99">ScienceDirect.com - Trends in Food Science & Technology - L-theanine—a unique amino acid of green tea and its relaxation effect in humans http://www.sciencedirect.com/science/article/pii/S0924224499000448 </ref>
<ref name="CaffTeaDementSong12">Tea and cognitive health in late life: c... [J Nutr Health Aging. 2012] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/22237999 </ref>
<ref name="CaffTeaObesityZhen04">Anti-obesity Effects of Three Major Components of Green Tea, Catechins, Caffeine and Theanine, in Mice http://iv.iiarjournals.org/content/18/1/55.short </ref>
<ref name="CaffTheanRoge08">Time for tea: mood, blood pressure... [Psychopharmacology (Berl). 2008] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/17891480 </ref>
<ref name="CaffTheanBrya08">Psychological effects of dietary components of tea:... [Nutr Rev. 2008] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/18254874 </ref>
<ref name="CaffTheanWimp07">Source density analysis of the human E... [Nutr Neurosci. 2007 Jun-Aug] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/18019399 </ref>
<ref name="CaffTheanTopo09">The effects of L-theanine on alpha-band oscilla... [Brain Topogr. 2009] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/18841456 </ref>
<ref name="CaffTheanNobr08">L-theanine, a natural constituent in te... [Asia Pac J Clin Nutr. 2008] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/18296328 </ref>
<ref name="CaffEGCGObesity">ingentaconnect Novel Treatments for Obesity and Osteoporosis: Targeting Apoptoti... http://www.ingentaconnect.com/content/ben/cmc/2005/00000012/00000019/art00003 </ref>
<ref name="CaffEGCGCancerCerv">Apoptotic effect of green tea polyphenol (EGCG) on cervical carcinoma cells - Asif Siddiqui - 2010 - Diagnostic Cytopathology - Wiley Online Library http://onlinelibrary.wiley.com/doi/10.1002/dc.21434/abstract </ref>
<ref name="CaffEGCGCancer">Apoptotic effect of EGCG in HT-29 colon cancer cells via AMPK signal pathway http://www.sciencedirect.com/science/article/pii/S0304383506001960 </ref>
<ref name="CaffTeaAntiOx">Oxygen Radical Absorbance Capacity (ORAC) of Selected Foods – 2007 http://www.webcitation.org/query?url=http%3A%2F%2Fwww.ars.usda.gov%2FSP2UserFiles%2FPlace%2F12354500%2FData%2FORAC%2FORAC07.pdf&date=2009-05-23 </ref>
<ref name="CaffPainAdjuvant">JAMA Network | JAMA: The Journal of the American Medical Association | Caffeine as an Analgesic Adjuvant http://jama.jamanetwork.com/article.aspx?articleid=392180 </ref>
<ref name="CafIsolationHeadache">The analgesic effects of caffeine in headache. [Pain. 1991] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/2052380 </ref>
<ref name="CafDOMSMice2">Intracellular calcium and force in single mouse mu... [J Physiol. 1995] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/8568662 </ref>
<ref name="CafDOMSMice1">Excitation-contraction uncoupling: major... [Exerc Sport Sci Rev. 2001] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/11337828 </ref>
<ref name="CafDOMSForce">Caffeine Attenuates Delayed-Onset Muscle Pain and Force Loss Following Eccentric Exercise http://www.jpain.org/article/S1526-5900%2806%2901023-6/abstract </ref>
<ref name="CafPainDomsVol">The effects of caffeine on perceived pain of muscles http://scholarsresearchlibrary.com/ABR-vol2-iss6/ABR-2011-2-6-16-21.pdf</ref>
<ref name="CafParaPainSurgery">Analgesic efficacy of paracetamol and its combination with codeine and caffeine in surgical pain–a meta-analysis - Zhang - 2008 - Journal of Clinical Pharmacy and Therapeutics - Wiley Online Library http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2710.1996.tb01148.x/abstract </ref>
<ref name="CafCoffGreen05">Coffee, tea and diabetes: the role of weig... [Int J Obes (Lond). 2005] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/15925959?dopt=Abstract </ref>
<ref name="CafCoffDam06">Coffee, Caffeine, and Risk of Type 2 Diabetes http://care.diabetesjournals.org/content/29/2/398.abstract?ijkey=0aa1ab4745bc811da4ab34ed66604d4462b97615&keytype2=tf_ipsecsha </ref>
<ref name="CafCoffWu05">Caffeinated Coffee, Decaffeinated Coffee, and Caffeine in Relation to Plasma C-Peptide Levels, a Marker of Insulin Secretion, in U.S. Women http://care.diabetesjournals.org/content/28/6/1390.abstract?ijkey=3d4c0a5aa75e45f1690789634957ab9f0a6f0e13&keytype2=tf_ipsecsha </ref>
<ref name="CafCoffAoIMSala04">Annals of Internal Medicine | Coffee Consumption and Risk for Type 2 Diabetes Mellitus http://annals.org/article.aspx?volume=140&issue=1&page=1 </ref>
<ref name="CafCoffeeCancer">BMC Cancer | Full text | Coffee consumption and risk of cancers: a meta-analysis of cohort studies http://www.biomedcentral.com/1471-2407/11/96/ </ref>
<ref name="CafT2DM_SHBG">Coffee and Caffeine Consumption in Relation to Sex Hormone–Binding Globulin and Risk of Type 2 Diabetes in Postmenopausal Women http://diabetes.diabetesjournals.org/content/60/1/269.short </ref>
<ref name="CafT2DMSysRevDam05">JAMA Network | JAMA: The Journal of the American Medical Association | Coffee Consumption and Risk of Type 2 DiabetesA Systematic Review http://jama.jamanetwork.com/article.aspx?articleid=201177 </ref>
<ref name="CafCancerSong12">Increased Caffeine Intake Is Associated with Reduced Risk of Basal Cell Carcinoma of the Skin http://cancerres.aacrjournals.org/content/72/13/3282.abstract </ref>
<ref name="CafGluExNonExhThon02">Caffeine-Induced Impairment of Insulin Action but Not Insulin Signaling in Human Skeletal Muscle Is Reduced by Exercise http://diabetes.diabetesjournals.org/content/51/3/583.full </ref>
<ref name="CafGluRestInsResGrah01">ingentaconnect Caffeine ingestion elevates plasma insulin response in humans dur... http://www.ingentaconnect.com/content/nrc/cjpp/2001/00000079/00000007/art00002 </ref>
<ref name="CafGluRestObesePet04">Caffeine ingestion increases the insulin response to an oral-glucose-tolerance test in obese men before and after weight loss http://www.ajcn.org/content/80/1/22.short </ref>
<ref name="CafGluExGlycPed07">High rates of muscle glycogen resynthesis after exhaustive exercise when carbohydrate is coingested with caffeine http://www.jappl.org/content/105/1/7.full </ref>
<ref name="CafGluExGlycBatt03">Caffeine ingestion does not impede the resynthesis of proglycogen and macroglycogen after prolonged exercise and carbohydrate supplementation in humans http://jap.physiology.org/content/96/3/943.full </ref>
<ref name="CaffGlucRestPizz98">Effects of caffeine on glucose tolerance: a ... [Eur J Clin Nutr. 1998] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/9846599?dopt=Abstract </ref>
<ref name="CaffGlucRestKei02">Caffeine Can Decrease Insulin Sensitivity in Humans http://care.diabetesjournals.org/content/25/2/364.abstract?ijkey=0d78b20406d1b0da6a363f1b00847b0434751e49&keytype2=tf_ipsecsha </ref>
<ref name="CaffGlucExcNieu99">Gastrointestinal function during exercise: comparison of water, sports drink, and sports drink with caffeine http://jap.physiology.org/content/89/3/1079.full </ref>
<ref name="CaffGlucExcYeo05">Caffeine increases exogenous carbohydrate oxidation during exercise http://jap.physiology.org/content/99/3/844.full </ref>
<ref name="CaffMeta">Effects of caffeine ingestion o... [Int J Sport Nutr Exerc Metab. 2004] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/15657469</ref>
<ref name="CaffUse">Prevalence of caffeine use in elite ... [Appl Physiol Nutr Metab. 2011] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/21854160</ref>
<ref name="CaffWorld">Gilbert RM. Caffeine consumption. In : Spiller GA, editor. The methylxanthine beverages and foods, Alan R. Liss; 1984. p. 185-213</ref>
<ref name="CaffDependence">Psychopharmacology, Volume 94, Number 4 - SpringerLink http://www.springerlink.com/content/wl412194360xj32t/</ref>
<ref name="CaffDiuretic">Myth buster: caffeine does not exhibit a di... [Indian J Med Res. 2010] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/20693584</ref>
<ref name="CaffDiureticDose">Renal and cardiovascular effects of caffeine... [Clin Sci (Lond). 1987] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/3297472</ref>
<ref name="Caff11day">Fluid, electrolyte, and renal i... [Int J Sport Nutr Exerc Metab. 2005] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/16131696</ref>
<ref name="CaffTea">Black tea is not significantly different from wate... [Br J Nutr. 2011] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/21450118</ref>
<ref name="CaffSodium">Natriuretic effect of caffeine: assessment o... [Clin Sci (Lond). 2002] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/12401118</ref>
<ref name="CaffLionHeart">Search for the Competitive Edge: A History of Dietary Fads and Supplements http://jn.nutrition.org/content/127/5/869S.full</ref>
<ref name="CafModEx">Effects of moderate exercise on the pha... [Eur J Clin Pharmacol. 1991] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/2060565 </ref>
<ref name="CafExThermal">Effects of exercise and thermal stress on caf... [J Appl Physiol. 2002] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/12235049 </ref>
<ref name="CafAltitude">Caffeine at high altitude: java at base cAMP. [High Alt Med Biol. 2010] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/20367483 </ref>
<ref name="CafHabituated">European Journal of Applied Physiology and Occupational Physiology, Volume 62, Number 6 - SpringerLink http://www.springerlink.com/content/u37082130426tl56/ </ref>
<ref name="CafHabitAdren">Caffeine metabolism and epinephrine responses during exercise in users and nonusers http://jap.physiology.org/content/75/2/805.abstract </ref>
<ref name="CaffCoffee">Metabolic and exercise endurance effects of coffee and caffeine ingestion http://jap.physiology.org/content/85/3/883.abstract </ref>
<ref name="CaffMetaAndPerf">Caffeine and exercise: metabolism and per... [Can J Appl Physiol. 1994] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/8081318 </ref>
<ref name="CaffCoffeeCostill">Effects of caffeine ingestion on metabolism a... [Med Sci Sports. 1978] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/723503 </ref>
<ref name="CaffCoffeeWiles">Effect of caffeinated coffee on running speed, respiratory factors, blood lactate and perceived exertion during 1500-m treadmill running. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1478936/ </ref>
<ref name="CaffCoffeeCasal">Failure of caffeine to affect substrate... [Med Sci Sports Exerc. 1985] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/3982273 </ref>
<ref name="CaffCoffeeButts25">Butts and Crowell (1985) Effect of caffeine ingestion on cardiorespiratory endurance in men and women http://www.getcited.org/pub/103341768 </ref>
<ref name="DOMSTiming">Comparison of the symptoms of exercise-induced muscle damage after an initial and repeated bout of plyometric exercise in men and boys
http://jap.physiology.org/cgi/content/full/99/3/1174 </ref>
<ref name="CaffDecaffCoffeeGlucose">Coffee acutely modifies gastrointestinal hormone secretion and glucose tolerance in humans: glycemic effects of chlorogenic acid and caffeine http://www.ajcn.org/content/78/4/728.abstract </ref>
<ref name="CaffGlucKel03">Coffee acutely modifies gastrointestinal hormone secretion and glucose tolerance in humans: glycemic effects of chlorogenic acid and caffeine http://www.ajcn.org/content/78/4/728.abstract </ref>
<ref name="CaffGlucObT2DMEx">Caffeine Ingestion Is Associated With Reductions in Glucose Uptake Independent of Obesity and Type 2 Diabetes Before and After Exercise Training http://care.diabetesjournals.org/content/28/3/566.short </ref>
<ref name="CaffPostExcGlyc">High rates of muscle glycogen resynthesis after exhaustive exercise when carbohydrate is coingested with caffeine http://jap.physiology.org/content/105/1/7.long </ref>
<ref name="CafRPE">Effects of caffeine ingestion on rati... [Scand J Med Sci Sports. 2005] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/15773860 </ref>
<ref name="CafMusclePain">Effect of caffeine on quadricep... [Int J Sport Nutr Exerc Metab. 2009] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/19478340 </ref>
<ref name="CafMusclePainHeat">Caffeine lowers muscle pain during exercise in... [Physiol Behav. 2011] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/21163281 </ref>
<ref name="Graham-1991">{{Cite journal | last1 = Graham | first1 = TE. | last2 = Spriet | first2 = LL. | title = Performance and metabolic responses to a high caffeine dose during prolonged exercise. | journal = J Appl Physiol | volume = 71 | issue = 6 | pages = 2292-8 | month = Dec | year = 1991 | doi = | PMID = 1778925 }}</ref>
<ref name="Pasman-1995">{{Cite journal | last1 = Pasman | first1 = WJ. | last2 = van Baak | first2 = MA. | last3 = Jeukendrup | first3 = AE. | last4 = de Haan | first4 = A. | title = The effect of different dosages of caffeine on endurance performance time. | journal = Int J Sports Med | volume = 16 | issue = 4 | pages = 225-30 | month = May | year = 1995 | doi = 10.1055/s-2007-972996 | PMID = 7657415 }}</ref>
<ref name="CaffRedBull">Nutrition Facts and Analysis for Energy drink, RED BULL, with added caffeine, niacin, pantothenic acid, vitamins B6 and B12 http://nutritiondata.self.com/facts/beverages/7399/2 </ref>
<ref name="Macfarlane">{{cite book|author=Alan Macfarlane|coauthors=Iris Macfarlane|title=The Empire of Tea|publisher=The Overlook Press|isbn=1-58567-493-1|page=32|year=2004}}</ref>
<ref name="Lin-2003">{{Cite journal | last1 = Lin | first1 = YS. | last2 = Tsai | first2 = YJ. | last3 = Tsay | first3 = JS. | last4 = Lin | first4 = JK. | title = Factors affecting the levels of tea polyphenols and caffeine in tea leaves. | journal = J Agric Food Chem | volume = 51 | issue = 7 | pages = 1864-73 | month = Mar | year = 2003 | doi = 10.1021/jf021066b | PMID = 12643643 }}</ref>
<ref name="ShishikuraKhokhar2005">{{cite journal|last1=Shishikura|first1=Yoko|last2=Khokhar|first2=Santosh|title=Factors affecting the levels of catechins and caffeine in tea beverage: estimated daily intakes and antioxidant activity|journal=Journal of the Science of Food and Agriculture|volume=85|issue=12|year=2005|pages=2125–2133|issn=0022-5142|doi=10.1002/jsfa.2206}}</ref>
<ref name="Bunker-1979">{{Cite journal | last1 = Bunker | first1 = ML. | last2 = McWilliams | first2 = M. | title = Caffeine content of common beverages. | journal = J Am Diet Assoc | volume = 74 | issue = 1 | pages = 28-32 | month = Jan | year = 1979 | doi = | PMID = 762339 }}</ref>
<ref name="ChouBell2007">{{cite journal|last1=Chou|first1=K.-H.|last2=Bell|first2=L.N.|title=Caffeine Content of Prepackaged National-Brand and Private-Label Carbonated Beverages|journal=Journal of Food Science|volume=72|issue=6|year=2007|pages=C337–C342|issn=0022-1147|doi=10.1111/j.1750-3841.2007.00414.x}}</ref>
<ref name="CaffDeFizz">Fueling Properly for an Ultra | Running Times Magazine http://runningtimes.com/Article.aspx?ArticleID=21791 </ref>
<ref name="Buscicchio-2012">{{Cite journal | last1 = Buscicchio | first1 = G. | last2 = Piemontese | first2 = M. | last3 = Gentilucci | first3 = L. | last4 = Ferretti | first4 = F. | last5 = Tranquilli | first5 = AL. | title = The effects of maternal caffeine and chocolate intake on fetal heart rate. | journal = J Matern Fetal Neonatal Med | volume = 25 | issue = 5 | pages = 528-30 | month = May | year = 2012 | doi = 10.3109/14767058.2011.636104 | PMID = 22502981 }}</ref>
<ref name="CaffStarbucks">The Complete Guide to Starbucks Caffeine http://www.energyfiend.com/the-complete-guide-to-starbucks-caffeine </ref>
<ref name="CaffDatabase">Caffeine Content of Drinks http://www.energyfiend.com/the-caffeine-database\# </ref>
<ref name="Stern2011">{{cite journal|last1=Stern|first1=Judith|title=Coffee and muscle cramps|journal=Neuromuscular Disorders|volume=21|issue=5|year=2011|pages=375|issn=09608966|doi=10.1016/j.nmd.2011.03.007}}</ref>
<ref name="Dubowitz2011">{{cite journal|last1=Dubowitz|first1=Victor|title=Muscle cramps and coffee|journal=Neuromuscular Disorders|volume=21|issue=3|year=2011|pages=235|issn=09608966|doi=10.1016/j.nmd.2011.01.004}}</ref>
<ref name="Voermansvan Engelen2011">{{cite journal|last1=Voermans|first1=N.C.|last2=van Engelen|first2=B.G.|title=Coffee and muscle cramps|journal=Neuromuscular Disorders|volume=21|issue=12|year=2011|pages=832|issn=09608966|doi=10.1016/j.nmd.2011.07.006}}</ref>
<ref name="Venables-2008">{{Cite journal | last1 = Venables | first1 = MC. | last2 = Hulston | first2 = CJ. | last3 = Cox | first3 = HR. | last4 = Jeukendrup | first4 = AE. | title = Green tea extract ingestion, fat oxidation, and glucose tolerance in healthy humans. | journal = Am J Clin Nutr | volume = 87 | issue = 3 | pages = 778-84 | month = Mar | year = 2008 | doi = | PMID = 18326618 }}</ref>
</references>
Caffeine is widely consumed by the general public and athletes, and moderate levels can improve athletic performance. Caffeine does not cause dehydration, but it can interfere with sleep. Caffeine in coffee does not seem as effective, so other sources should be used.
=Intro=
Man has been searching for ways of improving athletic performance since at least 400 BC, when the hearts of lion were believed to impart benefits<ref name="CaffLionHeart"/>. Today, caffeine can improve performance in endurance running, and three of every four elite athletes take caffeine when competing<ref name="CaffUse"/>. Caffeine is one of the most widely used drugs in the world<ref name="CaffWorld"/>, with average daily intakes worldwide of 70mg/day, but higher in the US (~200mg/day) and the UK (~400mg/day)<ref name="CaffDependence"/>. Caffeine has many effects on many different tissue types, directly and through its metabolites, as well as stimulating adrenaline release<ref name="CaffMetaAndPerf"/>.
=Performance =
Studies have shown caffeine can improve performance by ~2%<ref name="CaffMeta"/>. Though much greater improvements (~12%) have been shown in laboratory conditions, these are not likely to be seen in real world race conditions<ref name="CaffMeta"/>. That ~2% represents 3.5 minutes on a 3 hour marathon, nearly 5 minutes on a 4 hour marathon. For the 5K, that represents 25 seconds on a 21 minute 5K, or 18 seconds on a 15 minute 5K. Caffeine tends to benefit fitter individuals more<ref name="CaffMeta"/>. Caffeine may improve performance by reducing the [[Rating of Perceived Exertion|RPE]]<ref name="CafRPE"/> and muscle pain<ref name="CafMusclePain"/>.
==Green Tea and Performance==
There is relatively little research concerning the effect of tea on athletic performance. However, one study did show that the green tea extract increased fat burning and glucose tolerance during cycling at 60% [[VO2max|V̇O<sub>2</sub>max]] without affecting heart rate or overall energy consumption<ref name="Venables-2008"/>.
==Coffee and Performance==
When you take caffeine as coffee, it may not improve performance as it does when taken in other forms. One study showed that caffeine in coffee does not give a performance improvement where isolated caffeine does<ref name="CaffCoffee"/> and another showed no benefit from caffeinated coffee over decaffeinated coffee<ref name="CaffCoffeeButts25"/>. Some studies show a performance benefit from caffeinated coffee<ref name="CaffCoffeeWiles"/><ref name="CaffCoffeeCostill"/><ref name="CaffCoffeeCasal"/>, but did not compare with caffeine alone. This may be because coffee contains hundreds if not thousands of compounds besides caffeine<ref name="CaffMetaAndPerf"/><ref name="CafCoffeeCancer"/>. Some of these extra compounds of been shown to affect glucose metabolism<ref name="CafT2DMSysRevDam05"/>. It is been observed that decaffeinated coffee can reduce the absorption of glucose<ref name="CaffDecaffCoffeeGlucose"/>.
=How much?=
Most studies use 3-13mg/Kg, average 6mg, but within that dose range there was no obvious dose response<ref name="CaffMeta"/>. A smaller intake of 3 to 5 mg/kg dose before exercise and then 1 to 2 mg/kg intakes during prolonged exercise has been recommended<ref name="CaffMetaAndPerf"/>. Too much caffeine (9 mg/kg), especially for those that do not regularly take caffeine, can cause impairment, such as becoming talkative, giddy, and unable to perform simple tasks such as telling the time<ref name="CaffMetaAndPerf"/>. Low levels of exercise (30% [[VO2max|V̇O<sub>2</sub>max]]) seem to increase the metabolism of caffeine<ref name="CafModEx"/>, but higher intensities have no impact<ref name="CafExThermal"/>.
=Caffeine and Dehydration=
Caffeine does not impact performance in hot/humid conditions, nor act as a diuretic when running<ref name="CaffDiuretic"/>. Caffeine at 360mg is a diuretic at rest, but not at 180mg or less<ref name="CaffDiureticDose"/>. Caffeine does not cause long term dehydration<ref name="Caff11day"/>, and black tea has been shown to hydrate as well as water<ref name="CaffTea"/>. Caffeine does result in increased sodium excretion in the urine<ref name="CaffSodium"/>, but the significance of this unclear.
=Caffeine Habituation=
Surprisingly, there is no clear evidence that the performance benefits of caffeine vary with habitual caffeine usage<ref name="CaffMeta"/>. Caffeine impacts caffeine naive more at rest than those habituated to caffeine, but the difference is far less during exercise<ref name="CafHabituated"/>. Caffeine habituation has been shown to reduce the adrenaline response to caffeine, but most other responses remain similar <ref name="CafHabitAdren"/>. Animal studies have shown that some tissues adapt to long term use of caffeine but other tissues do not appear to change at all<ref name="CaffMetaAndPerf"/>.
=Caffeine and DOMS =
Caffeine has been shown to not only reduce the pain of [[Delayed Onset Muscle Soreness]] (DOMS)<ref name="CafPainDomsVol"/>, but also reduces the associated weakness<ref name="CafDOMSForce"/><ref name="CafDOMSMice1"/><ref name="CafDOMSMice2"/>. This reduction in weakness is important because although the soreness is delayed 24-72 hours after exercise, the muscle damage and resulting weakness happens within 30 minutes<ref name="DOMSTiming"/>.
=Caffeine Withdrawal=
Withdrawal from Caffeine generally produces a headache and fatigue, with some evidence of anxiety<ref name="CaffDependence"/>. Onset of withdrawal is typically 12-24 hours after the last intake, though occasionally as quickly as 3-6 hours, with symptoms after peaking 20-48 hours and lasting a week<ref name="CaffDependence"/>. Small amounts of caffeine can help with withdrawal.
[[File:Caffeine withdrawal and headache.jpg|none|thumb|300px|The onset and severity of headache with caffeine withdrawal.]]
[[File:Caffeine withdrawal and sleepy.jpg|none|thumb|300px|A similar chart of fatigue for caffeine withdrawal.]]
=Caffeine and Sleep=
Not surprisingly given it's a stimulant, caffeine interferes with [[Zeo Sleep Monitor|sleep]]. Taking 100mg caffeine just before bedtime significantly interferes with sleep<ref name="Landolt-1995"/>. More significantly, taking 200 mg early in the morning will also significantly interfere with sleep<ref name="Landolt-1995-2"/>. This suggests that caffeine should be taken as early in the day as is practical, and those with sleep problems should reduce caffeine or avoid it completely.
[[File:Caffeine and Sleep.jpg|none|thumb|300px|Caffeine concentrations measured in the saliva, with 200mg administered at 7:10am.]]
=Caffeine and Cramping=
There is no research around any possible link between caffeine and [[Cramps]], but there are a few anecdotal reports of a link between caffeine/coffee and [[Cramps]]<ref name="Stern2011"/><ref name="Dubowitz2011"/><ref name="Voermansvan Engelen2011"/>.
=Caffeine as a Pain killer=
Caffeine is frequently added to over-the-counter pain medication to boost its effectiveness; without caffeine 40% more pain medication is required to have the same results<ref name="CaffPainAdjuvant"/>. Caffeine adds slightly to the relief of surgical pain from Acetaminophen (Paracetamol)<ref name="CafParaPainSurgery"/> and caffeine can reduce headaches to an equivalent level as Acetaminophen (Paracetamol)<ref name="CafIsolationHeadache"/>. Caffeine reduces muscle pain during exercise in both those that habitually take caffeine and those that caffeine naïve<ref name="CafMusclePain"/>, though one study suggested this may only occur in hot conditions<ref name="CafMusclePainHeat"/>. As noted above, caffeine can reduce the pain of DOMS<ref name="CafPainDomsVol"/>.
=Caffeine at altitude=
The general recommendation to avoid caffeine at altitude does not seem to have a scientific basis. In fact, a number of the effects of caffeine have the potential to be beneficial at altitude<ref name="CafAltitude"/>
* As noted above, caffeine does not produce dehydration, and there is little evidence that dehydration contributes to altitude sickness.
* Caffeine tends to increase breathing, which may offset the depressed breathing seen at altitude.
* The risk of a brain or lung edema at altitude is a serious concern, and there is the possibility that caffeine may help by constricting blood vessels without restricting oxygenation.
* Caffeine may help alleviate the headache that is common with altitude sickness.
* The lassitude seen at altitude may be offset by caffeine, and the exercise performance improvements at altitude may be even greater than at sea level.
* While caffeine could reduce the altitude problems that prevent sleep, the stimulant nature of caffeine may offset these benefits.
Caffeine has a shorter duration of effect at high altitude, possibly due to increased blood flow to the liver, and withdrawal from caffeine would likely make altitude problems more severe<ref name="CafAltitude"/>.
=Glucose Absorption, Insulin Resistance and Glycemic index =
Caffeine changes the way glucose is absorbed, this effect is different before, during and after exercise.
==At Rest==
Caffeine reduces glucose absorption at rest<ref name="CaffGlucKel03"/><ref name="CaffGlucRestKei02"/><ref name="CaffGlucRestPizz98"/><ref name="CafGluRestInsResGrah01"/>. In tests on lean, obese, and Type 2 Diabetics, glucose absorption was impaired by caffeine, though exercise mitigated the reduction slightly in non-diabetics<ref name="CaffGlucObT2DMEx"/><ref name="CafGluRestObesePet04"/>.
==During Exercise==
Unlike the effect of caffeine on sedentary or resting individuals, caffeine increases the absorption, uptake and metabolism of glucose during exercise<ref name="CaffGlucExcYeo05"/><ref name="CaffGlucExcNieu99"/>. Caffeine taken during exercise does not change [[Glycogen]] replenishment post-exercise<ref name="CafGluExGlycBatt03"/>, but caffeine taken with carbohydrate after exercise increased [[Glycogen]] replenishment and insulin levels compared with just carbohydrate<ref name="CaffPostExcGlyc"/><ref name="CafGluExGlycPed07"/>. One hypothesis for this difference is that caffeine reduces the effect of insulin, and non-insulin dependent glucose pathways predominate during exercise<ref name="CafGluExGlycBatt03"/>. Caffeine taken 2 hours after exercise impairs glucose absorption, but to a lesser extent than in a completely rested state<ref name="CafGluExNonExhThon02"/>.
=Sources of Caffeine=
There are various sources of caffeine that are sometimes used by athletes.
==Coffee==
While coffee is a very common source of caffeine, there is evidence that caffeine taken in coffee is not as effective as other forms (see above for details). Also, coffee may cause [[Running and Stomach Problems|Stomach Problems]] and [[Running and Lower GI Problems|Lower GI Problems]] in some individuals. Typical brewed coffee contains 100-150mg per cup<ref name="Bunker-1979"/> which compounds the problem of using coffee in sports. I would recommend using other sources of caffeine before or during runs.
==Tea==
[[File:Caffeine Tea Brewing Time.jpg|right|thumb|200px|Brewing time and levels of Caffeine (CF), the catechins epigallocatechin gallate (EGCG), epicatechin gallate (ECG), epigallocatechin (EGC) and epicatechin (EC)<ref name="ShishikuraKhokhar2005"/>.]
It is claimed that tea is the second most popular drink after water<ref name="Macfarlane"/>, but it does not appear to be commonly used by athletes. Because the level of caffeine can vary dramatically with different types of tea, and different brewing methods, it is difficult to know how much caffeine is in a particular drink of tea. Generally black tea has more than oolong tea which has more than green tea<ref name="Lin-2003"/>. Typically black tea contains 28 to 46mg of Caffeine<ref name="Bunker-1979"/>. This unpredictability makes tea a problematic source of caffeine, though using the same tea and brewing for the same time will give reproducible levels, but you won't know the absolute caffeine intake.
==Gels ($2-8/100mg)==
Gels are available with and without caffeine, and the caffeinated variety normally has 25mg, though some go as high as 100mg. The higher caffeine concentrations often include a coffee extract, which may limit the benefits. Given that gels typically cost $1-2 per gel, the caffeine cost is $2-8/100mg. See [[Comparison of Energy Gels]] for more details.
==Soda==
The caffeine levels in soda vary widely, with some common values shown below.
{| class="wikitable"
!Soda!!Caffeine per 12oz<ref name="ChouBell2007"/>
|-
|Coca-Cola||33.9mg
|-
|Diet Coke ||46.3mg
|-
|Pepsi||38.9mg
|-
|Diet Pepsi||36.7mg
|-
|Dr Pepper|| 42.6mg
|-
|Diet Dr Pepper ||44.1mg
|-
|Mountain Dew ||54.8mg
|-
|Diet Mountain Dew||55.2mg
|-
|Vault Zero ||74mg
|-
|}
Typically soda makes a poor sports drink as it contains too much sugar, is too carbonated and additives like phosphoric acid can upset the digestive system. However, ultrarunners used to regularly use soda that had been left to go flat and then often diluted with water<ref name="CaffDeFizz"/>. This is something to practice in training before using during a race.
==Energy Drinks ==
There are many different types of energy drink available on the market today. Frequently they are a mixture of many different substances that are believed in some way to be stimulating. Energy drinks should be used with caution, as the substances they contain may not have been scientifically evaluated, especially in the combinations provided. Energy drinks often contain carbohydrate, but the specific types of carbohydrate and the concentration used may not be appropriate to athletic events. The caffeine content of energy drinks is often 200-300mg per can<ref name="CaffDatabase"/>, which is quite high, but lower than a Starbucks Venti brewed coffee which typically has 400+mg<ref name="CaffStarbucks"/>.
==Red Bull ($3-6/100mg)==
I've tried a few different energy drinks, and the only one I use now is Red Bull. Red Bull is only lightly carbonated, is not too sweet for my taste, and while the mixture of glucose and sucrose is not great for sports drink, it's better than many of the alternatives. I'm not sure if the added Taurine and B vitamins are beneficial, but the combination seems to work well for me. Red Bull contains about 80mg of caffeine per 8oz can<ref name="CaffRedBull"/>, which is slightly less than the equivalent volume of coffee.
==Energy Shots==
Energy shots are more convenient than energy drinks due to their small size and portability. However, they concentrated form can easily cause stomach upsets in addition to the problems noted in energy drinks above.
==Caffeine Tablets ($0.03/100mg)==
Caffeine tablets have the advantage of low-cost, predictable caffeine content, and portability. Compared with other sources of caffeine, these tablets are 1/100<sup>th</sup> the cost. I use [http://go.fellrnr.com?id=35454X937677&xs=1&url=http%3A%2F%2Fwww.amazon.com%2FNatrol-Caffeine-200mg-Tablets-100-Count%2Fdp%2FB000OPV118 Natrol] tables, which are 200mg per tablet. I cut them into halves using a [http://go.fellrnr.com?id=35454X937677&xs=1&url=http%3A%2F%2Fwww.amazon.com%2FApex-70068-Ultra-Pill-Splitter%2Fdp%2FB000EGKTGK Pill Cutter], then it's easy to bite off a smaller amount as needed. I carry these in my [[Portable Pharmacy]].
=Tea and Theanine=
Theanine is an amino acid found in tea, primarily green tea. Theanine calms the mind without inducing drowsiness, achieving a relaxed but alert mental state<ref name="CaffTheanNobr08"/>. Theanine has a number of benefits:
* It has been shown to improve and sustain long term attention<ref name="CaffTheanTopo09"/>, acting as a stimulant, even without caffeine<ref name="CaffTheanWimp07"/>.
* When combined with caffeine, theanine reduces distractions<ref name="CaffTheanBrya08"/>.
* Theanine reduces blood pressure<ref name="CaffTeaRelaxJune99"/> and can offset the rise in blood pressure that comes from caffeine<ref name="CaffTheanRoge08"/>.
* Three components of green tea (Catechins, Caffeine and Theanine) reduce obesity in mice<ref name="CaffTeaObesityZhen04"/>.
* Tea may help reduce dementia<ref name="CaffTeaDementSong12"/>, and tea improves learning in rats<ref name="CaffTeaRelaxJune99"/>.
* Theanine and cystine may help reduce the immune system depression of high intensity training<ref name="CaffTheanImune09"/><ref name="CaffTheanImune10"/>.
=Caffeine and health =
For most people, caffeine is generally taken as tea or coffee, to the bulk of the scientific evidence around the health impact of caffeine is based on these beverages.
==Tea ==
Both green and black tea contain similarly high levels of antioxidants<ref name="CaffTeaAntiOx"/>. Green tea contains high levels of [http://en.wikipedia.org/wiki/Epigallocatechin_gallate EGCG], which has been shown to inhibit cancer cell proliferation<ref name="CaffEGCGCancer"/><ref name="CaffEGCGCancerCerv"/>. This EGCG may help trigger natural cell death which in turn may help treat both obesity and osteoporosis<ref name="CaffEGCGObesity"/>. Green tea consumption has been linked to a reduction in upper GI cancers and green team may also help with lung, liver, prostate and breast cancers<ref name="CaffTeaCancer"/>.
==Coffee and Cancer==
Caffeine intake (coffee and other forms) is linked to lower rates of the most common type of skin cancer<ref name="CafCancerSong12"/> and coffee drinking is associated with a reduced risk of bladder, breast, buccal and pharyngeal, colorectal, endometrial, esophageal, hepatocellular, leukemic, pancreatic, and prostate cancers<ref name="CafCoffeeCancer"/>.
==Coffee and Type 2 Diabetes==
Coffee drinking is associated with a substantially lower risk of type 2 diabetes<ref name="CafT2DMSysRevDam05"/><ref name="CafCoffAoIMSala04"/>, including decaffeinated<ref name="CafCoffDam06"/>. However, coffee drinking is associated with a number of lifestyle risks, such as smoking, inactivity, and poor diet, and adjustments for these risks may overly strengthen the potential anti-diabetic benefits of coffee drinking<ref name="CafT2DMSysRevDam05"/>. There are a number of possible mechanisms behind the reduction in type II diabetes:
* In postmenopausal women, coffee increases the hormone [http://en.wikipedia.org/wiki/Sex_hormone-binding_globulin SHRB] that may account for the diabetes reduction <ref name="CafT2DM_SHBG"/>.
* Coffee (including decaffeinated) is correlated with reduced markers of insulin secretion, especially in obese and overweight women<ref name="CafCoffWu05"/>.
* One study found the T2DM risk was only reduced in tea and coffee drinkers who had previously lost weight<ref name="CafCoffGreen05"/>.
=Restrictions on Caffeine for Competition=
Caffeine was removed from the World Anti-Doping Agency (WADA) list in 2004; prior to that it was restricted at high levels based on urine concentration<ref name="CaffWADA"/>. It is still restricted by the NCAA at similarly high concentrations<ref name="CaffNCAA"/>. The level of caffeine intake required to exceed the NCAA threshold varies dramatically (x16) between individuals, and for a given individual at different times, with some people at risk of exceeding the permitted level on 3 cups of regular coffee per day and others able to take excessive levels<ref name="CaffUrineBrik91"/>. A study of caffeine showed that even 9mg/kg was less than the NCAA threshold for the test subjects<ref name="Graham-1991"/>, but another study showed that doses of 9mg or above could result in a positive test for some individuals<ref name="Pasman-1995"/>.
=Ethics of Caffeine=
At its most simplistic level, caffeine is permitted for use in competition, so if we consider "ethics" as simply "following the rules", then caffeine is ethical. If we look at the broader ethical implications of caffeine however, things become a little more nebulous. The World Anti-Doping Agency (WADA) may consider controlling a substance or method if it meets two of these three conditions:
# It has the potential to improve performance
# It has the potential to harm the health of the athlete
# It violates the "spirit of sport"
Clearly caffeine meets criteria \#1, but not \#2 (if anything, caffeine may be beneficial to health). So does the use of caffeine violate the spirit of the sport? Let's compare the use of caffeine with the use of carbohydrate:
* Both caffeine and carbohydrate have been shown to improve performance
* Neither caffeine nor carbohydrate are essential for life
* The vast majority of people routinely take caffeine, and nearly everybody takes carbohydrate
* There are few health risks with caffeine, and other than [[Fructose]], carbohydrate is generally considered safe
* While both caffeine and carbohydrate are found naturally in plants, it is common for them to be consumed in highly refined forms
* Athletes frequently consume caffeine and/or carbohydrate for the sole purpose of improving performance
* Any athlete that does not effectively use either caffeine or carbohydrate is at a distinct disadvantage
This comparison indicates to me that caffeine is not against the spirit of the sport, or unethical.
=Newborn babies and Caffeine =
Newborn babies may be subject to higher levels of caffeine from breast milk than one would expect. If we assume:
* A 3 Kg baby (6.6Lb)
* A milk intake of 500 to 900 ml/day<ref name="CaffBabyMilk"/>
* The nursing mother's caffeine intake of 200mg/day (one double shot espresso),
We get a resulting caffeine concentration in the milk of 4ug/ml to 8ug/ml<ref name="Stavchansky-"/>, which is a total caffeine intake of between 2mg to 13mg, or 0.6 to 4 mg/Kg body weight. The upper end of that level is quite high. However, the baby's half-life for caffeine is 60-100 hours, compared with an adult's 2-10 hour half-life, so the caffeine will build up over time. A 24 hour half live (which is easier to calculate) would result in about a 3mg to 26mg, which is 1 to 8 mg/Kg. I'm guessing that would result in the baby not sleeping well! Conversely, a baby whose mother takes caffeine during pregnancy and is then given formula milk may undergo caffeine withdrawal after birth<ref name="McGowan-1988"/>. Even if the mother breast feeds, the varying levels of caffeine may cause withdrawal symptoms<ref name="Martín-2007"/>. Also, caffeine has been shown to increase fetal heart rate<ref name="Buscicchio-2012"/>.
=References=
<references>
<ref name="Martín-2007">{{Cite journal | last1 = Martín | first1 = I. | last2 = López-Vílchez | first2 = MA. | last3 = Mur | first3 = A. | last4 = García-Algar | first4 = O. | last5 = Rossi | first5 = S. | last6 = Marchei | first6 = E. | last7 = Pichini | first7 = S. | title = Neonatal withdrawal syndrome after chronic maternal drinking of mate. | journal = Ther Drug Monit | volume = 29 | issue = 1 | pages = 127-9 | month = Feb | year = 2007 | doi = 10.1097/FTD.0b013e31803257ed | PMID = 17304161 }}</ref>
<ref name="McGowan-1988">{{Cite journal | last1 = McGowan | first1 = JD. | last2 = Altman | first2 = RE. | last3 = Kanto | first3 = WP. | title = Neonatal withdrawal symptoms after chronic maternal ingestion of caffeine. | journal = South Med J | volume = 81 | issue = 9 | pages = 1092-4 | month = Sep | year = 1988 | doi = | PMID = 3420441 }}</ref>
<ref name="Stavchansky-">{{Cite journal | last1 = Stavchansky | first1 = S. | last2 = Combs | first2 = A. | last3 = Sagraves | first3 = R. | last4 = Delgado | first4 = M. | last5 = Joshi | first5 = A. | title = Pharmacokinetics of caffeine in breast milk and plasma after single oral administration of caffeine to lactating mothers. | journal = Biopharm Drug Dispos | volume = 9 | issue = 3 | pages = 285-99 | month = | year = | doi = | PMID = 3395670 }}</ref>
<ref name="CaffBabyMilk">How much expressed milk will my baby need? : KellyMom http://www.kellymom.com/bf/pumping/milkcalc.html </ref>
<ref name="Landolt-1995-2">{{Cite journal | last1 = Landolt | first1 = HP. | last2 = Werth | first2 = E. | last3 = Borbély | first3 = AA. | last4 = Dijk | first4 = DJ. | title = Caffeine intake (200 mg) in the morning affects human sleep and EEG power spectra at night. | journal = Brain Res | volume = 675 | issue = 1-2 | pages = 67-74 | month = Mar | year = 1995 | doi = | PMID = 7796154 }}</ref>
<ref name="Landolt-1995">{{Cite journal | last1 = Landolt | first1 = HP. | last2 = Dijk | first2 = DJ. | last3 = Gaus | first3 = SE. | last4 = Borbély | first4 = AA. | title = Caffeine reduces low-frequency delta activity in the human sleep EEG. | journal = Neuropsychopharmacology | volume = 12 | issue = 3 | pages = 229-38 | month = May | year = 1995 | doi = 10.1016/0893-133X(94)00079-F | PMID = 7612156 }}</ref>
<ref name="CaffTeaCancer">Tea and cancer prevention: epidemiological stu... [Pharmacol Res. 2011] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/21419224 </ref>
<ref name="CaffTheanImune10">Cystine and Theanine Supplementation Restores High-Intensity... : The Journal of Strength & Conditioning Research http://journals.lww.com/nsca-jscr/Abstract/2010/03000/Cystine_and_Theanine_Supplementation_Restores.34.aspx </ref>
<ref name="CaffTheanImune09">Effects of oral supplementation wi... [Biosci Biotechnol Biochem. 2009] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/19352043 </ref>
<ref name="CaffUrineBrik91">Caffeine renal clearance and urine caffe... [Br J Clin Pharmacol. 1991] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/2049248 </ref>
<ref name="CaffNCAA">NCAA Banned Drug List - NCAA.org http://www.ncaa.org/wps/wcm/connect/public/NCAA/Health+and+Safety/Drug+Testing/Resources/NCAA+banned+drugs+list </ref>
<ref name="CaffWADA">2012 Prohibited List - World Anti-Doping Agency http://www.wada-ama.org/en/Resources/Q-and-A/2012-Prohibited-List/ </ref>
<ref name="CaffTeaRelaxJune99">ScienceDirect.com - Trends in Food Science & Technology - L-theanine—a unique amino acid of green tea and its relaxation effect in humans http://www.sciencedirect.com/science/article/pii/S0924224499000448 </ref>
<ref name="CaffTeaDementSong12">Tea and cognitive health in late life: c... [J Nutr Health Aging. 2012] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/22237999 </ref>
<ref name="CaffTeaObesityZhen04">Anti-obesity Effects of Three Major Components of Green Tea, Catechins, Caffeine and Theanine, in Mice http://iv.iiarjournals.org/content/18/1/55.short </ref>
<ref name="CaffTheanRoge08">Time for tea: mood, blood pressure... [Psychopharmacology (Berl). 2008] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/17891480 </ref>
<ref name="CaffTheanBrya08">Psychological effects of dietary components of tea:... [Nutr Rev. 2008] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/18254874 </ref>
<ref name="CaffTheanWimp07">Source density analysis of the human E... [Nutr Neurosci. 2007 Jun-Aug] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/18019399 </ref>
<ref name="CaffTheanTopo09">The effects of L-theanine on alpha-band oscilla... [Brain Topogr. 2009] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/18841456 </ref>
<ref name="CaffTheanNobr08">L-theanine, a natural constituent in te... [Asia Pac J Clin Nutr. 2008] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/18296328 </ref>
<ref name="CaffEGCGObesity">ingentaconnect Novel Treatments for Obesity and Osteoporosis: Targeting Apoptoti... http://www.ingentaconnect.com/content/ben/cmc/2005/00000012/00000019/art00003 </ref>
<ref name="CaffEGCGCancerCerv">Apoptotic effect of green tea polyphenol (EGCG) on cervical carcinoma cells - Asif Siddiqui - 2010 - Diagnostic Cytopathology - Wiley Online Library http://onlinelibrary.wiley.com/doi/10.1002/dc.21434/abstract </ref>
<ref name="CaffEGCGCancer">Apoptotic effect of EGCG in HT-29 colon cancer cells via AMPK signal pathway http://www.sciencedirect.com/science/article/pii/S0304383506001960 </ref>
<ref name="CaffTeaAntiOx">Oxygen Radical Absorbance Capacity (ORAC) of Selected Foods – 2007 http://www.webcitation.org/query?url=http%3A%2F%2Fwww.ars.usda.gov%2FSP2UserFiles%2FPlace%2F12354500%2FData%2FORAC%2FORAC07.pdf&date=2009-05-23 </ref>
<ref name="CaffPainAdjuvant">JAMA Network | JAMA: The Journal of the American Medical Association | Caffeine as an Analgesic Adjuvant http://jama.jamanetwork.com/article.aspx?articleid=392180 </ref>
<ref name="CafIsolationHeadache">The analgesic effects of caffeine in headache. [Pain. 1991] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/2052380 </ref>
<ref name="CafDOMSMice2">Intracellular calcium and force in single mouse mu... [J Physiol. 1995] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/8568662 </ref>
<ref name="CafDOMSMice1">Excitation-contraction uncoupling: major... [Exerc Sport Sci Rev. 2001] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/11337828 </ref>
<ref name="CafDOMSForce">Caffeine Attenuates Delayed-Onset Muscle Pain and Force Loss Following Eccentric Exercise http://www.jpain.org/article/S1526-5900%2806%2901023-6/abstract </ref>
<ref name="CafPainDomsVol">The effects of caffeine on perceived pain of muscles http://scholarsresearchlibrary.com/ABR-vol2-iss6/ABR-2011-2-6-16-21.pdf</ref>
<ref name="CafParaPainSurgery">Analgesic efficacy of paracetamol and its combination with codeine and caffeine in surgical pain–a meta-analysis - Zhang - 2008 - Journal of Clinical Pharmacy and Therapeutics - Wiley Online Library http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2710.1996.tb01148.x/abstract </ref>
<ref name="CafCoffGreen05">Coffee, tea and diabetes: the role of weig... [Int J Obes (Lond). 2005] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/15925959?dopt=Abstract </ref>
<ref name="CafCoffDam06">Coffee, Caffeine, and Risk of Type 2 Diabetes http://care.diabetesjournals.org/content/29/2/398.abstract?ijkey=0aa1ab4745bc811da4ab34ed66604d4462b97615&keytype2=tf_ipsecsha </ref>
<ref name="CafCoffWu05">Caffeinated Coffee, Decaffeinated Coffee, and Caffeine in Relation to Plasma C-Peptide Levels, a Marker of Insulin Secretion, in U.S. Women http://care.diabetesjournals.org/content/28/6/1390.abstract?ijkey=3d4c0a5aa75e45f1690789634957ab9f0a6f0e13&keytype2=tf_ipsecsha </ref>
<ref name="CafCoffAoIMSala04">Annals of Internal Medicine | Coffee Consumption and Risk for Type 2 Diabetes Mellitus http://annals.org/article.aspx?volume=140&issue=1&page=1 </ref>
<ref name="CafCoffeeCancer">BMC Cancer | Full text | Coffee consumption and risk of cancers: a meta-analysis of cohort studies http://www.biomedcentral.com/1471-2407/11/96/ </ref>
<ref name="CafT2DM_SHBG">Coffee and Caffeine Consumption in Relation to Sex Hormone–Binding Globulin and Risk of Type 2 Diabetes in Postmenopausal Women http://diabetes.diabetesjournals.org/content/60/1/269.short </ref>
<ref name="CafT2DMSysRevDam05">JAMA Network | JAMA: The Journal of the American Medical Association | Coffee Consumption and Risk of Type 2 DiabetesA Systematic Review http://jama.jamanetwork.com/article.aspx?articleid=201177 </ref>
<ref name="CafCancerSong12">Increased Caffeine Intake Is Associated with Reduced Risk of Basal Cell Carcinoma of the Skin http://cancerres.aacrjournals.org/content/72/13/3282.abstract </ref>
<ref name="CafGluExNonExhThon02">Caffeine-Induced Impairment of Insulin Action but Not Insulin Signaling in Human Skeletal Muscle Is Reduced by Exercise http://diabetes.diabetesjournals.org/content/51/3/583.full </ref>
<ref name="CafGluRestInsResGrah01">ingentaconnect Caffeine ingestion elevates plasma insulin response in humans dur... http://www.ingentaconnect.com/content/nrc/cjpp/2001/00000079/00000007/art00002 </ref>
<ref name="CafGluRestObesePet04">Caffeine ingestion increases the insulin response to an oral-glucose-tolerance test in obese men before and after weight loss http://www.ajcn.org/content/80/1/22.short </ref>
<ref name="CafGluExGlycPed07">High rates of muscle glycogen resynthesis after exhaustive exercise when carbohydrate is coingested with caffeine http://www.jappl.org/content/105/1/7.full </ref>
<ref name="CafGluExGlycBatt03">Caffeine ingestion does not impede the resynthesis of proglycogen and macroglycogen after prolonged exercise and carbohydrate supplementation in humans http://jap.physiology.org/content/96/3/943.full </ref>
<ref name="CaffGlucRestPizz98">Effects of caffeine on glucose tolerance: a ... [Eur J Clin Nutr. 1998] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/9846599?dopt=Abstract </ref>
<ref name="CaffGlucRestKei02">Caffeine Can Decrease Insulin Sensitivity in Humans http://care.diabetesjournals.org/content/25/2/364.abstract?ijkey=0d78b20406d1b0da6a363f1b00847b0434751e49&keytype2=tf_ipsecsha </ref>
<ref name="CaffGlucExcNieu99">Gastrointestinal function during exercise: comparison of water, sports drink, and sports drink with caffeine http://jap.physiology.org/content/89/3/1079.full </ref>
<ref name="CaffGlucExcYeo05">Caffeine increases exogenous carbohydrate oxidation during exercise http://jap.physiology.org/content/99/3/844.full </ref>
<ref name="CaffMeta">Effects of caffeine ingestion o... [Int J Sport Nutr Exerc Metab. 2004] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/15657469</ref>
<ref name="CaffUse">Prevalence of caffeine use in elite ... [Appl Physiol Nutr Metab. 2011] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/21854160</ref>
<ref name="CaffWorld">Gilbert RM. Caffeine consumption. In : Spiller GA, editor. The methylxanthine beverages and foods, Alan R. Liss; 1984. p. 185-213</ref>
<ref name="CaffDependence">Psychopharmacology, Volume 94, Number 4 - SpringerLink http://www.springerlink.com/content/wl412194360xj32t/</ref>
<ref name="CaffDiuretic">Myth buster: caffeine does not exhibit a di... [Indian J Med Res. 2010] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/20693584</ref>
<ref name="CaffDiureticDose">Renal and cardiovascular effects of caffeine... [Clin Sci (Lond). 1987] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/3297472</ref>
<ref name="Caff11day">Fluid, electrolyte, and renal i... [Int J Sport Nutr Exerc Metab. 2005] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/16131696</ref>
<ref name="CaffTea">Black tea is not significantly different from wate... [Br J Nutr. 2011] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/21450118</ref>
<ref name="CaffSodium">Natriuretic effect of caffeine: assessment o... [Clin Sci (Lond). 2002] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/12401118</ref>
<ref name="CaffLionHeart">Search for the Competitive Edge: A History of Dietary Fads and Supplements http://jn.nutrition.org/content/127/5/869S.full</ref>
<ref name="CafModEx">Effects of moderate exercise on the pha... [Eur J Clin Pharmacol. 1991] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/2060565 </ref>
<ref name="CafExThermal">Effects of exercise and thermal stress on caf... [J Appl Physiol. 2002] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/12235049 </ref>
<ref name="CafAltitude">Caffeine at high altitude: java at base cAMP. [High Alt Med Biol. 2010] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/20367483 </ref>
<ref name="CafHabituated">European Journal of Applied Physiology and Occupational Physiology, Volume 62, Number 6 - SpringerLink http://www.springerlink.com/content/u37082130426tl56/ </ref>
<ref name="CafHabitAdren">Caffeine metabolism and epinephrine responses during exercise in users and nonusers http://jap.physiology.org/content/75/2/805.abstract </ref>
<ref name="CaffCoffee">Metabolic and exercise endurance effects of coffee and caffeine ingestion http://jap.physiology.org/content/85/3/883.abstract </ref>
<ref name="CaffMetaAndPerf">Caffeine and exercise: metabolism and per... [Can J Appl Physiol. 1994] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/8081318 </ref>
<ref name="CaffCoffeeCostill">Effects of caffeine ingestion on metabolism a... [Med Sci Sports. 1978] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/723503 </ref>
<ref name="CaffCoffeeWiles">Effect of caffeinated coffee on running speed, respiratory factors, blood lactate and perceived exertion during 1500-m treadmill running. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1478936/ </ref>
<ref name="CaffCoffeeCasal">Failure of caffeine to affect substrate... [Med Sci Sports Exerc. 1985] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/3982273 </ref>
<ref name="CaffCoffeeButts25">Butts and Crowell (1985) Effect of caffeine ingestion on cardiorespiratory endurance in men and women http://www.getcited.org/pub/103341768 </ref>
<ref name="DOMSTiming">Comparison of the symptoms of exercise-induced muscle damage after an initial and repeated bout of plyometric exercise in men and boys
http://jap.physiology.org/cgi/content/full/99/3/1174 </ref>
<ref name="CaffDecaffCoffeeGlucose">Coffee acutely modifies gastrointestinal hormone secretion and glucose tolerance in humans: glycemic effects of chlorogenic acid and caffeine http://www.ajcn.org/content/78/4/728.abstract </ref>
<ref name="CaffGlucKel03">Coffee acutely modifies gastrointestinal hormone secretion and glucose tolerance in humans: glycemic effects of chlorogenic acid and caffeine http://www.ajcn.org/content/78/4/728.abstract </ref>
<ref name="CaffGlucObT2DMEx">Caffeine Ingestion Is Associated With Reductions in Glucose Uptake Independent of Obesity and Type 2 Diabetes Before and After Exercise Training http://care.diabetesjournals.org/content/28/3/566.short </ref>
<ref name="CaffPostExcGlyc">High rates of muscle glycogen resynthesis after exhaustive exercise when carbohydrate is coingested with caffeine http://jap.physiology.org/content/105/1/7.long </ref>
<ref name="CafRPE">Effects of caffeine ingestion on rati... [Scand J Med Sci Sports. 2005] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/15773860 </ref>
<ref name="CafMusclePain">Effect of caffeine on quadricep... [Int J Sport Nutr Exerc Metab. 2009] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/19478340 </ref>
<ref name="CafMusclePainHeat">Caffeine lowers muscle pain during exercise in... [Physiol Behav. 2011] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/21163281 </ref>
<ref name="Graham-1991">{{Cite journal | last1 = Graham | first1 = TE. | last2 = Spriet | first2 = LL. | title = Performance and metabolic responses to a high caffeine dose during prolonged exercise. | journal = J Appl Physiol | volume = 71 | issue = 6 | pages = 2292-8 | month = Dec | year = 1991 | doi = | PMID = 1778925 }}</ref>
<ref name="Pasman-1995">{{Cite journal | last1 = Pasman | first1 = WJ. | last2 = van Baak | first2 = MA. | last3 = Jeukendrup | first3 = AE. | last4 = de Haan | first4 = A. | title = The effect of different dosages of caffeine on endurance performance time. | journal = Int J Sports Med | volume = 16 | issue = 4 | pages = 225-30 | month = May | year = 1995 | doi = 10.1055/s-2007-972996 | PMID = 7657415 }}</ref>
<ref name="CaffRedBull">Nutrition Facts and Analysis for Energy drink, RED BULL, with added caffeine, niacin, pantothenic acid, vitamins B6 and B12 http://nutritiondata.self.com/facts/beverages/7399/2 </ref>
<ref name="Macfarlane">{{cite book|author=Alan Macfarlane|coauthors=Iris Macfarlane|title=The Empire of Tea|publisher=The Overlook Press|isbn=1-58567-493-1|page=32|year=2004}}</ref>
<ref name="Lin-2003">{{Cite journal | last1 = Lin | first1 = YS. | last2 = Tsai | first2 = YJ. | last3 = Tsay | first3 = JS. | last4 = Lin | first4 = JK. | title = Factors affecting the levels of tea polyphenols and caffeine in tea leaves. | journal = J Agric Food Chem | volume = 51 | issue = 7 | pages = 1864-73 | month = Mar | year = 2003 | doi = 10.1021/jf021066b | PMID = 12643643 }}</ref>
<ref name="ShishikuraKhokhar2005">{{cite journal|last1=Shishikura|first1=Yoko|last2=Khokhar|first2=Santosh|title=Factors affecting the levels of catechins and caffeine in tea beverage: estimated daily intakes and antioxidant activity|journal=Journal of the Science of Food and Agriculture|volume=85|issue=12|year=2005|pages=2125–2133|issn=0022-5142|doi=10.1002/jsfa.2206}}</ref>
<ref name="Bunker-1979">{{Cite journal | last1 = Bunker | first1 = ML. | last2 = McWilliams | first2 = M. | title = Caffeine content of common beverages. | journal = J Am Diet Assoc | volume = 74 | issue = 1 | pages = 28-32 | month = Jan | year = 1979 | doi = | PMID = 762339 }}</ref>
<ref name="ChouBell2007">{{cite journal|last1=Chou|first1=K.-H.|last2=Bell|first2=L.N.|title=Caffeine Content of Prepackaged National-Brand and Private-Label Carbonated Beverages|journal=Journal of Food Science|volume=72|issue=6|year=2007|pages=C337–C342|issn=0022-1147|doi=10.1111/j.1750-3841.2007.00414.x}}</ref>
<ref name="CaffDeFizz">Fueling Properly for an Ultra | Running Times Magazine http://runningtimes.com/Article.aspx?ArticleID=21791 </ref>
<ref name="Buscicchio-2012">{{Cite journal | last1 = Buscicchio | first1 = G. | last2 = Piemontese | first2 = M. | last3 = Gentilucci | first3 = L. | last4 = Ferretti | first4 = F. | last5 = Tranquilli | first5 = AL. | title = The effects of maternal caffeine and chocolate intake on fetal heart rate. | journal = J Matern Fetal Neonatal Med | volume = 25 | issue = 5 | pages = 528-30 | month = May | year = 2012 | doi = 10.3109/14767058.2011.636104 | PMID = 22502981 }}</ref>
<ref name="CaffStarbucks">The Complete Guide to Starbucks Caffeine http://www.energyfiend.com/the-complete-guide-to-starbucks-caffeine </ref>
<ref name="CaffDatabase">Caffeine Content of Drinks http://www.energyfiend.com/the-caffeine-database\# </ref>
<ref name="Stern2011">{{cite journal|last1=Stern|first1=Judith|title=Coffee and muscle cramps|journal=Neuromuscular Disorders|volume=21|issue=5|year=2011|pages=375|issn=09608966|doi=10.1016/j.nmd.2011.03.007}}</ref>
<ref name="Dubowitz2011">{{cite journal|last1=Dubowitz|first1=Victor|title=Muscle cramps and coffee|journal=Neuromuscular Disorders|volume=21|issue=3|year=2011|pages=235|issn=09608966|doi=10.1016/j.nmd.2011.01.004}}</ref>
<ref name="Voermansvan Engelen2011">{{cite journal|last1=Voermans|first1=N.C.|last2=van Engelen|first2=B.G.|title=Coffee and muscle cramps|journal=Neuromuscular Disorders|volume=21|issue=12|year=2011|pages=832|issn=09608966|doi=10.1016/j.nmd.2011.07.006}}</ref>
<ref name="Venables-2008">{{Cite journal | last1 = Venables | first1 = MC. | last2 = Hulston | first2 = CJ. | last3 = Cox | first3 = HR. | last4 = Jeukendrup | first4 = AE. | title = Green tea extract ingestion, fat oxidation, and glucose tolerance in healthy humans. | journal = Am J Clin Nutr | volume = 87 | issue = 3 | pages = 778-84 | month = Mar | year = 2008 | doi = | PMID = 18326618 }}</ref>
</references>