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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|V?OV̇O<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|V?OV̇O<sub>2</sub>max]]) seem to increase the metabolism of caffeine<ref name="CafModEx"/>, but higher intensities have no impact<ref name="CafExThermal"/>. Below is a listing of caffeine in common beverages.
{| class="wikitable"
!'''Source'''!!'''Caffeine (mg)'''
|-
|Brewed coffee||100-150+ per 8oz
|-
|Brewed decaf coffee||5 (range: 3-12)
|-
|Starbucks Espresso||75 per shot
|-
|Black Tea||28-46 per 8Oz
|-
|Oolong Tea||12-55 per 8Oz
|-
|Green Tea||8-36 per 8Oz
|-
|Soda - Cola||35 per 12oz Can (see 'soda' for details)
|-
|Soda – Mountain Dew||54 per 12oz Can |-|Red Bull||80 per 8.3oz Can
|-
| Red Bull
| 80 per 8.3oz Can
|}
=Caffeine and Dehydration=
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[[Breathing]], which may offset the depressed breathing [[Breathing]] seen at [[Altitude Training| 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.
==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 per 8oz cup<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.
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 Coca-Cola||4633.3mg9mg
|-
|PepsiDiet Coke ||3846.9mg 3mg
|-
|Diet Pepsi||3638.7mg 9mg
|-
|Dr PepperDiet Pepsi|| 4236.6mg 7mg
|-
|Diet Dr Pepper ||44 42.1mg 6mg
|-
|Mountain Dew Diet Dr Pepper ||5444.8mg1mg
|-
|Diet Mountain Dew||5554.2mg8mg
|-
|Vault Zero Diet Mountain Dew||74mg55.2mg
|-
| 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.
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. One study has shown that the added Taurine, B vitamins and other ingredients do not add any benefit over the just taking the caffeine<ref name="Pettitt-2012"/>. However, I like the taste, and my expectation of a benefit provides a useful placebo. 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.
[http://en.wikipedia.org/wiki/Cardiac_arrhythmia Cardiac arrhythmias] (irregular heartbeats) are a group of conditions where the heart does not beat normally and can be a life threatening emergency. There is a common belief that caffeine is linked to some types of arrhythmias, but this does not seem scientifically supported for <ref name="RashidHines2006"/><ref name="Katan-2005"/><ref name="Pelchovitz-2011"/>. In fact, an animal study showed that moderate caffeine reduces the risk of atrial fibrillation<ref name="RashidHines2006"/>. A study giving recent heart attacks 450mg of caffeine showed no change in the risk of arrythmia<ref name="Myers-1990"/>. Giving 200mg of caffeine before a bicycle stress test to patients who have malignant ventricular arrhythmias made no difference<ref name="Graboys-1989"/>. However, there are anecdotal reports of people having arrhythmia triggered by caffeine. Note that a caffeine overdoes can result in heart problems<ref name="Pelchovitz-2011"/>.
==Evaluating the risks==
Because coronary artery disease may not have any initial symptoms<ref name="MayoCAD"/>, risk evaluation is tricky. Some runners who died suddenly had high cholesterol, high blood pressure or chest pains<ref name="WallerRoberts1980"/>. Other risk factors include diabetes, smoking, family history of heart attacks, obesity, long term alcohol use. If you have any risk factors for coronary artery disease, it would be prudent to talk to a healthcare professional.
=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.
<ref name="Pasman-1995">WJ. Pasman, MA. van Baak, AE. Jeukendrup, A. de Haan, The effect of different dosages of caffeine on endurance performance time., Int J Sports Med, volume 16, issue 4, pages 225-30, May 1995, doi [http://dx.doi.org/10.1055/s-2007-972996 10.1055/s-2007-972996], PMID [http://www.ncbi.nlm.nih.gov/pubmed/7657415 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">Alan Macfarlane, Iris Macfarlane !!coauthors!!, The Empire of Tea, publisher The Overlook Press !!publisher!!, isbn 1-58567-493-1, 32 !!page!!, 2004</ref>
<ref name="Lin-2003">YS. Lin, YJ. Tsai, JS. Tsay, JK. Lin, Factors affecting the levels of tea polyphenols and caffeine in tea leaves., J Agric Food Chem, volume 51, issue 7, pages 1864-73, Mar 2003, doi [http://dx.doi.org/10.1021/jf021066b 10.1021/jf021066b], PMID [http://www.ncbi.nlm.nih.gov/pubmed/12643643 12643643]</ref>
<ref name="ShishikuraKhokhar2005">Yoko Shishikura, Santosh Khokhar, Factors affecting the levels of catechins and caffeine in tea beverage: estimated daily intakes and antioxidant activity, Journal of the Science of Food and Agriculture, volume 85, issue 12, 2005, pages 2125–2133, ISSN [http://www.worldcat.org/issn/0022-5142 0022-5142], doi [http://dx.doi.org/10.1002/jsfa.2206 10.1002/jsfa.2206]</ref>
<ref name="Buscicchio-2012">G. Buscicchio, M. Piemontese, L. Gentilucci, F. Ferretti, AL. Tranquilli, The effects of maternal caffeine and chocolate intake on fetal heart rate., J Matern Fetal Neonatal Med, volume 25, issue 5, pages 528-30, May 2012, doi [http://dx.doi.org/10.3109/14767058.2011.636104 10.3109/14767058.2011.636104], PMID [http://www.ncbi.nlm.nih.gov/pubmed/22502981 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">Judith Stern, Coffee and muscle cramps, Neuromuscular Disorders, volume 21, issue 5, 2011, pages 375, ISSN [http://www.worldcat.org/issn/09608966 09608966], doi [http://dx.doi.org/10.1016/j.nmd.2011.03.007 10.1016/j.nmd.2011.03.007]</ref>
<ref name="Dubowitz2011">Victor Dubowitz, Muscle cramps and coffee, Neuromuscular Disorders, volume 21, issue 3, 2011, pages 235, ISSN [http://www.worldcat.org/issn/09608966 09608966], doi [http://dx.doi.org/10.1016/j.nmd.2011.01.004 10.1016/j.nmd.2011.01.004]</ref>