Moderate caffeine consumption is associated with higher levels of estrogen in Asian women, but lower levels in white women, according to a study of reproductive-age women conducted by the National Institutes of Health and other institutions.
Over 250 women, ages 18 to 44 years old, participated in the study between 2005 and 2007. On average, they consumed 90 milligrams of caffeine a day, equivalent to approximately one cup of caffeinated coffee.
Asian women who took in an average of 200 milligrams or more of caffeine a day — the equivalent of approximately two cups of coffee — had higher estrogen levels than women who consumed less caffeine.
In contrast, 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; however, the 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. Drinking 200 milligrams or more of caffeine from coffee was consistent with the findings for overall caffeine consumption—with Asians having higher estrogen levels, whites having lower estrogen levels, and the results for blacks not statistically significant. However, drinking more than one cup each day of caffeinated soda or green tea was linked to higher estrogen level in Asians, whites, and blacks.
The changes in estrogen levels among the participants did not seem to affect ovulation. Animal studies had suggested that caffeine could possibly interfere with ovulation.
“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.”
Most of the study participants 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.
During each visit, the participants reported what they had eaten in the last 24 hours and answered questions about their exercise, sleep, smoking and other lifestyle factors. Reproductive hormone levels were also measured.
Researchers added that receiving these details during multiple stages across two menstrual cycles produced more precise information concerning the link between caffeine and hormones than was possible in previous studies. The researchers also noted that the study volunteers were more racially diverse than those from earlier studies.
The study was published online in the American Journal of Clinical Nutrition.
Source: National Institutes of Health