The Surprising Impact of Caffeine on Women's Estrogen Levels
Health LibraryLatest Research in Women's Health
The Surprising Impact of Caffeine on Women's Estrogen Levels

Recent research by the National Institutes of Health (NIH) has unveiled intriguing insights into how caffeine consumption influences estrogen levels in women. This comprehensive study, published in the American Journal of Clinical Nutrition, highlights the differential effects of caffeine on women of various ethnic backgrounds, emphasizing the complex relationship between caffeine intake and hormonal balance.

Key Findings from the NIH Study

Ethnic Differences in Estrogen Levels:

  • Asian Women: The study found that Asian women who consumed an average of 200 milligrams or more of caffeine daily—approximately two cups of coffee—exhibited elevated estrogen levels compared to those who consumed less. This suggests that caffeine may enhance estrogen production or alter its metabolism in this group.
  • White Women: In contrast, white women who consumed the same amount of caffeine experienced slightly lower estrogen levels. This inverse relationship indicates that caffeine might reduce estrogen levels or affect its regulatory mechanisms differently in white women.
  • Black Women: For black women, high caffeine intake was associated with elevated estrogen levels; however, this result was not statistically significant, indicating that the findings for this group are less conclusive.

Sources of Caffeine:

The study calculated total caffeine intake from various sources, including coffee, black tea, green tea, and caffeinated soda. Interestingly, the impact of caffeine on estrogen levels varied slightly depending on the source:

  • Coffee: The effects mirrored those of overall caffeine consumption, with Asians showing elevated estrogen levels, whites showing reduced levels, and non-significant results for blacks.
  • Caffeinated Soda and Green Tea: Higher consumption of these beverages was linked to elevated estrogen levels in all ethnic groups studied, indicating that the type of caffeinated beverage might influence hormonal outcomes.

Impact on Ovulation:

  • Despite changes in estrogen levels, the study found no significant effects on ovulation among the participants. This contrasts with animal studies suggesting that caffeine might interfere with ovulation, highlighting the need for further research to understand these differences fully.

Implications for Women's Health

The findings from this study have significant implications for women's health, particularly for those of childbearing age. Estrogen plays a critical role in various physiological processes, and fluctuations in its levels can influence conditions such as endometriosis, osteoporosis, and certain cancers (endometrial, breast, and ovarian). Given that 89% of U.S. women aged 18-34 consume caffeine equivalent to 1.5 to two cups of coffee daily, understanding these hormonal impacts is crucial for developing better health guidelines.

Dr. Enrique Schisterman, a co-author of the study, emphasized the importance of considering caffeine consumption in future research on estrogen-related disorders. Long-term caffeine intake could potentially influence estrogen levels over extended periods, warranting careful consideration in studies investigating reproductive health and associated conditions.

Study Methodology and Participant Diversity

The study involved over 250 women aged 18-44 who participated between 2005 and 2007. On average, they consumed 90 milligrams of caffeine daily. The participants visited the study clinic multiple times across two menstrual cycles, providing detailed information about their diet, lifestyle, and reproductive hormone levels. This rigorous methodology allowed for precise measurement of the link between caffeine and estrogen levels.

Moreover, the study's diverse participant pool provided a broader understanding of how caffeine affects women from different ethnic backgrounds, offering valuable insights that can inform personalized health recommendations.


The NIH study sheds light on the nuanced relationship between caffeine consumption and estrogen levels in women, highlighting significant ethnic differences. These findings underscore the need for personalized approaches to dietary and health guidelines, taking into account individual variability in hormonal responses to caffeine. As research continues, it will be essential to explore the long-term implications of caffeine on women's health and refine our understanding of its role in hormonal regulation.

  • NIH Study shows caffeine consumption linked to estrogen changes;
1.Key Findings from the NIH Study
2.Implications for Women's Health
3.Study Methodology and Participant Diversity