NIH: Study shows caffeine consumption linked to estrogen changes

Will Starbucks be tobacco-ized for causing endometriosis, osteoporosis, and endometrial, breast, and ovarian cancers?

But typical caffeine intake is not credibly associated with any adverse health effects.

Below is the NIH media release.


NIH Study shows caffeine consumption linked to estrogen changes

Moderate caffeine intake associated with higher level for Asians, lower for whites

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 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 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 percent of U.S. women from 18-34 years of age consume the caffeine equivalent of 1.5 to two cups of coffee a day.

The study’s first author was Karen C. Schliep, Ph. D., M.S.P.H., from the University of Utah, Salt Lake City, who conducted the study during a research appointment at NICHD. Dr. Schliep undertook the research with Dr. Schisterman and colleagues at the University of Utah, the NICHD and the State University of New York at Buffalo.

More than 250 women from 18 to 44 years old participated in the study between 2005 and 2007. On average, they consumed 90 milligrams of caffeine a day, approximately equivalent to one cup of caffeinated coffee.

Most of the participants in the study reported to the study clinic one to three times a week for two menstrual cycles. Their visits were scheduled to correspond with specific stages of the menstrual cycle. At the visits, the women reported what they had eaten in the last 24 hours and answered questions about their exercise, sleep, smoking and other aspects of their lifestyle and reproductive hormone levels were measured in blood. The study authors noted that collection of these details during multiple time points across two menstrual cycles produced more precise information about the link between caffeine and hormones than was possible in earlier studies. The researchers also noted that the study participants were more racially diverse than those who took part in previous studies.

About the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD): The NICHD sponsors research on development, before and after birth; maternal, child, and family health; reproductive biology and population issues; and medical rehabilitation. For more information, visit the Institute’s website at

About the National Institutes of Health (NIH): NIH, the nation’s medical research agency, includes 27 Institutes and Centers and is a component of the U.S. Department of Health and Human Services. NIH is the primary federal agency conducting and supporting basic, clinical, and translational medical research, and is investigating the causes, treatments, and cures for both common and rare diseases. For more information about NIH and its programs, visit

5 thoughts on “NIH: Study shows caffeine consumption linked to estrogen changes”

  1. Publication standards have really fallen. Peer review used to consign studies “linking” cause and effects to the round circular file.

  2. Sounds like another effort by survey researchers. Not all coffee is Starbucks. Was theophylline or bromophylline likewise quantified by survey methods or were they just ignored? This is not a study. Just a survey report, correlated with lab data to imply that this is, somehow, scientific. Hardly worth reporting. Truly junk, with a shot at tenure, or a govt. job not far off.

  3. Also not mentioned: what is the normal variation of estrogen levels within the given population groups; was the resulting estrogen levels after the increase/decrease still within the normal boundry or outside, and if outside by how much; what were the estrogen levels of the participants after one, two, or three menstral cycles without any caffeine (i.e. do the study authors even know that the caffeine had any effect whatsoever or are they assuming any delta from some mean was caused by the caffeine); and what is the impact on health of varying levels of estrogen, and based on what evidence? The fact that these essential issues are not addressed in the story leads one to believe that the answers either aren’t know, reflecting poorly on the study authors ability to design a study, or the answers wouldn’t imply the problem the authors are implying in their press release, reflecting poorly on the honesty of the authors.

  4. “Some studies show coffee is bad for you”

    “Recent research indicates coffee may be very beneficial”.
    “Coffee is bad for you!”
    “Coffee is good for you!”
    “Coffee is bad for you!”
    “Coffee good for you!”
    Ad infinitum

  5. Unless there’s a good biological reason for it, I think the conflicting results across different ethnic groups pretty much invalidates the idea that caffeine raises estrogen levels in women. This summary does not mention the amount of increases they were seeing, however I’m betting it was low. Otherwise they would have been trumpeting it.

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