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{{DISPLAYTITLE:Caffeine and Running}}[[File:Caffeine.jpg|right|thumb|500px|Common sources of Caffeine.]]Caffeine can improve athletic performance, but it's as widely misunderstood as it is widely consumed by the general public and athletes, and moderate used. * Moderate levels of caffeine can improve athletic performanceby about 2%, which is about 5 minutes on a 4 hour marathon. This improvement appears to happen regardless of how regularly caffeine is used. * For running, the best recommendation is a dose of 3 to 5 mg/kg before exercise, followed by 1 to 2 mg/kg periodically after that. For runners, a [[Comparison of Energy Gels| caffeinated energy gel]] is probably the best source. * While it's commonly believed that caffeine causes hydration, this is only true when high doses are given to those not used to it. Drinking a caffeinated beverage will produce about the same amount of urine, which is probably the source of the myth. Caffeine does People will drink caffeinated beverages when they're not cause dehydrationthirsty, but so they assume it 's the caffeine that's causing them to need to urinate, not the fluid they've drunk. * Obviously caffeine can interfere with sleep, but this effect can last much longer than you might expect. Even caffeine taken early in the morning can impact your nights' sleep. * Caffeine in coffee does not seem as effective at improving performance, so other sources should be used. * Caffeine increases blood pressure, and should be avoided during exercise by those with high blood pressure.
=Introduction=
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"/>.
=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"/>. Below is a listing of caffeine in common beverages.
{| class="wikitable"
! '''Source'''
! '''Caffeine (mg) '''
Caffeine raises blood pressure during exercise, increasing the possibility of excessively high blood pressure. Caffeine can increase or decrease heart rate during exercise, possibly lowering it during lower intensity exercise and increasing it at highest intensities.
* The effect of Caffeine on heart rate during exercise is ambiguous, with some studies showing an increase in heart rate<ref name="Bell-1998"/><ref name="Mcnaughton1987"/><ref name="Sasaki-1987"/><ref name="Sung-1995"/><ref name="Bell-2002"/>, while others show a decrease<ref name="Sullivan-1992"/><ref name="TurleyGerst2006"/><ref name="Gaesser-1985"/><ref name="McClaranWetter2007"/><ref name="SungLovallo1990"/>. Examining the studies in more detail however, and it appears that the increase in heart rate may be mostly at the highest intensities, with caffeine reducing heart rate at the lower intensities. The effect does not appear different for those that are caffeine habituated or those that are caffeine naïve.
{| class="wikitable"
! Study
! Subjects
* 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"/>.
=Caffeine clearance=
Caffeine is metabolized by the liver enzyme CYP1A2<ref name="KalowTang1993"/>, and the activity of this enzyme can be effected by drugs and diet, with tobacco and chargrilled meat increasing levels<ref name="Flockhart-2007"/>. (There is a common genetic mutation in dogs that prevents the formation of CYP1A2, making these dogs unable to metabolize caffeine and some other substances<ref name="AretzGeyer2011"/>.)
=Glucose Absorption, Insulin Resistance and Glycemic index =
Caffeine changes the way glucose is absorbed, but this effect is different for those at rest compared with those exercising.
==Soda==
The caffeine levels in soda vary widely, with some common values shown below.
{| class="wikitable"
! Soda
! Caffeine per 12oz<ref name="ChouBell2007"/>
<ref name="Nishijima-2002">Y. Nishijima, T. Ikeda, M. Takamatsu, Y. Kiso, H. Shibata, T. Fushiki, T. Moritani, Influence of caffeine ingestion on autonomic nervous activity during endurance exercise in humans., Eur J Appl Physiol, volume 87, issue 6, pages 475-80, Oct 2002, doi [http://dx.doi.org/10.1007/s00421-002-0678-1 10.1007/s00421-002-0678-1], PMID [http://www.ncbi.nlm.nih.gov/pubmed/12355185 12355185]</ref>
<ref name="Green-1996">PJ. Green, J. Suls, The effects of caffeine on ambulatory blood pressure, heart rate, and mood in coffee drinkers., J Behav Med, volume 19, issue 2, pages 111-28, Apr 1996, PMID [http://www.ncbi.nlm.nih.gov/pubmed/9132505 9132505]</ref>
<ref name="KalowTang1993">Werner Kalow, Bing-Kou Tang, The use of caffeine for enzyme assays: A critical appraisal, Clinical Pharmacology and Therapeutics, volume 53, issue 5, 1993, pages 503–514, ISSN [http://www.worldcat.org/issn/0009-9236 0009-9236], doi [http://dx.doi.org/10.1038/clpt.1993.63 10.1038/clpt.1993.63]</ref>
<ref name="Flockhart-2007">Flockhart DA. Drug Interactions: Cytochrome P450 Drug Interaction Table. Indiana University School of Medicine (2007). "/clinpharm/ddis/clinical-table/" Accessed June 2015.</ref>
<ref name="AretzGeyer2011">J. S. Aretz, J. Geyer, Detection of the CYP1A2 1117C > T polymorphism in 14 dog breeds, Journal of Veterinary Pharmacology and Therapeutics, volume 34, issue 1, 2011, pages 98–100, ISSN [http://www.worldcat.org/issn/01407783 01407783], doi [http://dx.doi.org/10.1111/j.1365-2885.2010.01222.x 10.1111/j.1365-2885.2010.01222.x]</ref>
</references>