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The JAMA study looked at the effects of this slow metabolizing gene on the incidence of heart attack. If you’re a slow metabolizer, your risk of heart attack rises exponentially if you drink multiple cups of coffee a day. If you are under the age of 59, your risk of heart attack soars.
Stephen Cherniske in Caffeine Blues first put forward the theory in 1998 that caffeine consumption causes heart attacks, or myocardial infarctions in scientific terms, by causing arteries feeding the heart to spasm. He pointed out that the incidence of death from heart attack in people with perfectly clear arteries occurs in about 20% of heart attack cases. Open the newspaper and you frequently read about someone who was athletic, in good health and dropped dead of a heart attack. Their age? Typically, in their forties or fifties with no prior indication of heart disease.
The JAMA study looked at 2,014 people who had survived a heart attack and matched them with 2,014 healthy people in the general population. For people with the slow metabolizing variation of the gene, the risk of heart attack for 2-3 cups of coffee a day was increased 36% and for 4 or more cups of coffee a day, the risk went up to 64%. These numbers may seem quite significant themselves, but when the researchers looked at younger people where heart disease is less prevalent, they found that caffeine increased the risk for heart attack in slow metabolizers exponentially. For people under the age of 59, the risk went up 24% for just 1 cup of coffee a day, 67% for 2-3 cups a day, and a whopping 133% for 4 or more cups a day. Under the age of 50, the risk increased 4 fold!
The difference in the genetic metabolism of caffeine explains why we constantly hear conflicting results about one caffeine study versus another. Of course many studies are funded by the coffee industry and thus optimal study results are produced by skewing the participants selected for the study. For instance, studies about caffeine and heart disease typically exclude people with a condition called Mitral Valve Prolapse (MVP). But 7-10% of the population has MVP and thus the results exclude data on people who would be highly susceptible to the affects of caffeine on their hearts.
Last week a new heart study published in the Journal of Circulation announced that after looking at the dietary habits of 120,000 people they found no effect of drinking multiple cups of coffee a day on the incidence of heart disease. But the lead researcher admitted that a study of this size may not reveal how caffeine affects heart disease in people who have the slow metabolizing gene.
"We can’t exclude the association between coffee consumption and the risk of coronary heart disease in small groups of people," said Rob van Dam, a research scientist at the Harvard School of Public Health, and a co-author of the study. For instance, a recent study suggested that one form of a gene responsible for metabolism of caffeine could make coffee harmful to people who carry the gene, van Dam said."
In other words, in a study this size, the people with the fast gene may have cancelled out the people with the slow gene. But approximately 40-50% of the population has the slow metabolizing gene – not exactly a "small group" of people!
More to the point, the lead researcher of the caffeine gene study, Professor El Sohemy of the University of Toronto, stated, the caffeine gene study "clearly illustrates that one size does not fit all. Perhaps in the future we'll be making different [dietary] recommendations based on people’s genetic makeup."
Another good example of how large studies dilute the results for smaller subsets of caffeine-sensitive people is the studies about fibrocystic breast disease and women. Large studies of all women don’t prove a correlation between caffeine and fibrocystic breast disease, but studies of women who have fibrocystic breasts find that taking them off of caffeine relieves their symptoms. Maybe future studies will see if these women have the slow metabolizing gene causing their breast tissue to become more sensitive to caffeine!
Unfortunately there is no commercial test to tell us if we have the slow or fast metabolizing variation of this gene. But if we take note of our bodies’ response to caffeine, the message should be loud and clear. Do multiple cups of coffee increase your jitteriness, irritability, anxiety, or rapid heart beat? Do you suffer from high blood pressure, difficulty falling asleep, or energy swings throughout the day? Is everyday stress hard to cope with, making you short-tempered and causing muscle tension especially in the neck, shoulders, and back? If you’re a woman, do you suffer from PMS, breast pain with fibrocystic lumps, infertility, or menopausal symptoms like hot flashes, mood swings, and disturbed sleep?
All these types of reactions to coffee are good indicators that caffeine consumption is affecting your health. You don’t need a genetic test to get your body’s message; stay away from coffee and caffeine!
1. Cornelis, M. C., El-Sohemy, A., Kabagambe, E.K., and Campos, H., 2006. Coffee, CYP1A2 Geontype, and Risk of Myocardial Infarction., Journal of the American Medical Association. 295(10):1135-1141.
2. Lopez-Garcia, E., van Dam, R.M., Willett, W.C., et al., 2006 Coffee Consumption and Coronary Heart Disease in Mean and Women: A Prospective Cohort Study., Circulation 113(17):2045-2053.
3. Edelson, Ed. Heavy Coffee Drinking Doesn’t Hurt the Heart, Health Day News, April 24th, 2006.
4. Tanner, Lindsay. Slow Caffeine Metabolism Could Spell Heart Trouble, The Boston Globe, March 8, 2006.
