By ANAHAD O’CONNOR / nytimes.com
Your daily dose of caffeine may tinker with more than just your energy levels.
A new study of women ages 18 to 44 found that drinking coffee and other caffeinated beverages can alter levels of estrogen. But the impact varies by race. In white women, for example, coffee appears to lower estrogen, while in Asian women it has the reverse effect, raising levels of the hormone.
The study did not look at older women, but women of child-bearing age who enjoy a daily cuppa have little reason to fret, the researchers said. The effects of caffeine on estrogen are so minimal that in healthy women, it has no impact on ovulation or overall health, at least in the short term.
“This is important physiologically because it helps us understand how caffeine is metabolized by different genetic groups,” said Dr. Enrique Schisterman, an author of the study and senior investigator at the National Institutes of Health. “But for women of reproductive age, drinking coffee will not alter their hormonal function in a clinically significant way.”
The study, which was published in The American Journal of Clinical Nutrition, analyzed data on more than 250 women who were examined one to three times a week over two menstrual cycles. They provided blood samples along with details about behaviors like exercise, eating and smoking. On average, they consumed about 90 milligrams of caffeine a day, equivalent to roughly one cup of coffee.
After controlling for a number of variables, like age and diet, the researchers found that among Asian women, those who had 200 milligrams or more of caffeine a day had higher estrogen levels compared to those who consumed less. A similar pattern was seen among black women, though it was not statistically significant. In white women, however, 200 milligrams or more of caffeine appeared to have a slight lowering effect on estrogen.