Changes

* 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|V̇O₂max]]) 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.

! '''Source'''

! '''Caffeine (mg) '''

| 80 per 8.3oz Can

|}

=Caffeine, Blood Pressure and Heart Rate=

Caffeine increases blood pressure at rest and under stress, including exercise stress. The effect of caffeine on heart rate is unclear, with both increases and decreases observed in studies. Generally caffeine decreases heart rate at rest and moderate intensity exercise, but increases it at maximal workloads.

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.

! Study

! Subjects

==Soda==

The caffeine levels in soda vary widely, with some common values shown below.

! Soda

! Caffeine per 12oz<ref name="ChouBell2007"/>

<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>