Caffeine intake may change a woman’s estrogen levels: Study

By Dr. Ananya Mandal, MDJan 31 2012

According to latest research caffeine may alter women’s estrogen levels, and 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 raise them.

The researchers analyzed the women 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.

Results showed that 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.

However researchers note that overall health and ovulation did not get significantly altered due to these changes in estrogen. “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 said.

However Schisterman adds that it is unclear why the relationship exists 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.

Dr. Schisterman noted that while healthy, premenopausal women should not worry about caffeine intake in the short term, more research was needed to see if there could be a cumulative impact over many years or decades. “We don’t know if there are long-term effects of these small shifts in hormonal levels,” he said.

There has been research that shows 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.