Asian women who consumed an average of 200 milligrams or more of caffeine a day — the equivalent of roughly two cups of coffee — had elevated estrogen levels when compared to Asian women who consumed less, according to a study of reproductive-age women by researchers at the National Institutes of Health and other institutions.
However, white women who consumed 200 milligrams or more of caffeine a day had slightly lower estrogen levels than white women who consumed less. Black women who consumed 200 milligrams or more of caffeine a day had elevated estrogen levels, but this increased amount was not enough to be statistically significant.
Total caffeine intake was calculated from coffee, black tea, green tea and caffeinated soda. Findings differed slightly when the source of caffeine was considered individually. Consuming 200 milligrams or more of caffeine from coffee mirrored the findings for overall caffeine consumption, with Asians having elevated estrogen levels, whites having lower estrogen levels and the results for blacks not statistically significant. However, consumption of more than one cup each day of caffeinated soda or green tea was associated with a higher estrogen level in Asians, whites and blacks.
The changes in estrogen levels among the women who took part in the study did not appear to affect ovulation. Previous studies conducted in animals suggested that caffeine might interfere with ovulation.
“The results indicate that caffeine consumption among women of child-bearing age influences estrogen levels,” said Enrique Schisterman, PhD, of the Division of Epidemiology, Statistics and Prevention Research at the Eunice Kennedy Shriver National Institute of Child Health and Human Development, part of NIH.
“Short-term, these variations in estrogen levels among different groups do not appear to have any pronounced effects. We know that variations in estrogen level are associated with such disorders as endometriosis, osteoporosis and endometrial, breast and ovarian cancers. Because long-term caffeine consumption has the potential to influence estrogen levels over a long period of time, it makes sense to take caffeine consumption into account when designing studies to understand these disorders.”
The study authors noted that 89% of U.S. women from ages 18 to 34 consume the caffeine equivalent of 1.5 to two cups of coffee a day.
The study appeared last week on the website of the American Journal of Clinical Nutrition. To read a summary and access the study via subscription or purchase, visit www.ajcn.org/content/95/2/488.abstract.