All Coffee Drinkers Aren’t Equal

Caffeine may affect people differently based on genetic expression of enzymes

April 28, 2012 / Author:  / Reviewed by: Robert Carlson, M.D

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(dailyRx News) Caffeine can be a legal way to enhance athletic performance, though studies have shown mixed results. Genetic variation may be the reason caffeine does not work the same for everyone.

Many studies have shown that caffeine can increase a person’s athletic performance, but these studies have also shown that these effects are not universal throughout the participants.

A new study examines the link between caffeine’s effects and genetic differences between people.

"Caffeine may give you an extra edge in sports."

Dr. Christopher J. Womack, PhD, a researcher and professor at James Madison University’s Department of Kinesiology authored this study. Womack and his research team found that caffeine’s effects are closely tied to a particular gene that controls the expression of the cytochrome enzyme CYP1A2.

Cytochrome enzyme CYP1A2 is an important enzyme for drug metabolism found in the intestines and liver, which means that it plays a key role in how the body processes nutrients and molecules that a person takes in.

There are two forms of the gene that controls this enzyme. One is called A allele, and the other is called C allele. Alleles are two or more different forms of a gene or group of genes that are responsible for different traits, such as hair color or blood type.

This study examined the effects of caffeine on the athletic activity of 35 recreationally competitive cyclists. Sixteen of these cyclists had the A allele for CYP1A2, while the other 19 had the C allele.

After a 12-hour fast (and a 24-hour abstinence from caffeine) each cyclist was put through a simulated 40 km time trial on a stationary bike in a laboratory setting.

An hour before the time trial, each participant was randomly given a pill containing either 6mg-kg of caffeine or of white flour (placebo). Neither the cyclists nor the researcher who personally gave each cyclist the pill knew whether it was the caffeine pill or the placebo.

After calculating the results of these simulated trials, Womack and his team noticed differences between the performances of one group compared to the others.

Compared with the placebo results of the time trial, the results of A allele group while on caffeine were an average of 3.8 minutes faster. The C allele group was only 1.8 minutes faster on average with the addition of caffeine compared to the C allele participants who received a placebo.

Previous studies have shown that people with different gene expression of CYP1A2 metabolize caffeine at different rates. This is due to differences in how their CYP1A2 turns on and processes molecules. People with the A allele for this enzyme produce an enzyme that works faster than people with the C allele.

Womack and his team acknowledge that further studies into CYP1A2 on the effects of caffeine should include measurements of caffeine metabolites, which are the molecules CYP1A2 converts caffeine into.

These measurements would allow the researchers to determine what caused the change in performance between the A allele group and the C allele group. By looking at the participant’s blood chemistry, they would be able to determine if the difference in effects was caused by caffeine itself or by metabolites of caffeine.

Regardless of the different effects, caffeine was still shown to increase performance for both groups.

Since caffeine is a very safe chemical for most healthy individuals, it seems it could be an effective, and legal, performance enhancing substance. However, this enhancement may be greater for some people than in others.

This study was completed in 2011 and was published in the March 2012 volume of Journal of the International Society of Sports Nutrition. There were no reported conflicts of interest.

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Review Date: 
April 26, 2012
Last Updated:
May 10, 2012