Asian women who consumed an average of 200 milligrams or more of caffeine a daythe equivalent of roughly two cups of coffeehad elevated estrogen levels when compared to 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 women who consumed less. Black women who consumed 200 milligrams or more of caffeine a day were found to have elevated estrogen levels, but this result was not statistically significant.
Total caffeine intake was calculated from any of the following sources: coffee, black tea, green tea, and caffeinated soda.
Findings differed slightly when the source of caffeine was considered singly. 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. Studies conducted in animals had suggested that caffeine might interfere with ovulation.
The study was published online in the American Journal of Clinical Nutrition.
"The results indicate that caffeine consumption among women of child-bearing age influences estrogen levels," said Enrique Schisterman, Ph.D., of the Division of Epidemiology, Statistics and Prevention Research at the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), the NIH institute where some of the research was conducted. "Short term, these variations in estrogen levels am
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NIH/National Institute of Child Health and Human Development