Caffeine and estradiol: a complicated relationship

As little as two cups of caffeinated coffee per day is enough to lower free estradiol concentrations in white women and raise them in Asian women. As little as one cup of caffeinated soda or green tea is enough to increase free estradiol concentrations among women of all races.

The findings come from a small study conducted from 2005 to 2007 by the Eunice Kennedy Shriver National Institute of Child Health and Human Development. Researchers followed 259 participants for up to two menstrual cycles. Participants provided fasting blood samples for hormonal assessment.

On average, the women consumed 90 mg of caffeine per day, equivalent to one cup of caffeinated coffee. Overall, 66% of caffeine intake came from coffee, 17% from tea, 14% from soda, 3% from chocolate, and 0.003% from caffeinated medications.

Black women who consumed 200 mg or more per day from coffee had slightly elevated estradiol levels, but the increase was not statistically significant. All the changes in estradiol levels were insufficient to affect ovulation.

The authors noted that almost 90% of American women between the ages of 18 and 34 years consume the caffeine equivalent of 1.5 to 2 cups of coffee per day. They concluded that interactions between race and caffeine intake on total and free estradiol concentrations are significant and require more research.

Schliep KC, Schisterman EF, Mumford SL, et al. Caffeinated beverage intake and reproductive hormones among premenopausal women in the BioCycle Study. Am J Clin Nutr. 2012;95(27):488-497.