Study: Caffeine May Alter Estrogen Levels in Women

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For women, that morning cup o’ joe may act as more than just a pick-me-up. New research shows that caffeine may alter women’s estrogen levels, and that such changes differ according to race.

The study, published in the American Journal of Clinical Nutrition, looked at more than 250 women ages 18 to 44, and found that for white women, caffeine appeared to lower estrogen levels, while in Asian women it seemed to raised them.

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The women were analyzed one to three times a week over two menstrual cycles. Exercise, eating and smoking behaviors were recorded and reviewed with blood samples. On average, the women consumed about 90 milligrams of caffeine per day, the equivalent to a cup of coffee.

Among Asian women, those who consumed 200 milligrams of caffeine or more per day had higher estrogen levels than those who drank less. The opposite was true among white women: those who consumed at least 200 milligrams of caffeine a day had lower levels of estrogen. The results in black women were similar to those in Asians, but did not reach statistical significance.

The good news is that, in terms of overall health and ovulation, these changes in estrogen had no meaningful impact on healthy women. “For women of reproductive age, drinking coffee will not alter their hormonal function in a clinically significant way,” Dr. Enrique Schisterman, senior investigator at the National Institutes of Health and author of the study, told the New York Times.

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It’s not clear why caffeine may affect women differently by race, according to Schisterman, but he suggests that the influence of genetics on metabolism may play a role. The researchers also found differences depending on the source of women’s caffeine. For instance, when researchers isolated the effect of caffeine from beverages like green tea and soda, they found it was associated with higher estrogen in women of all races. It’s possible that the level of antioxidants in various beverages, as well as other added ingredients in coffee, such as sugar and milk, may modify caffeine’s effect.

Overall, however, the researchers said that healthy young women need not worry about their caffeine consumption. What’s more, other research shows that drinking coffee actually has health benefits like reducing the risk of stroke and depression, and staving off diseases like cancer, Type 2 diabetes, Parkinson’s and dementia.

Thankfully, there is no need to skip that coffee break.

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