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.”
Coffee May Boost Estrogen Levels in Women
Drinking more than two cups of coffee daily may boost estrogen levels in women and could exacerbate conditions such as endometriosis and breast pain, study findings suggest.
According to the researchers, women who drank the most coffee had higher levels of estradiol, a naturally occurring form of estrogen, during the early follicular phase, or days 1 to 5 of the menstrual cycle.
``Higher estrogen levels would not be beneficial for women who for example have endometriosis, breast pain and family histories of breast or ovarian cancer, especially arising premenopausally,’’ the study’s lead author, Dr. Daniel W. Cramer from Brigham and Women’s Hospital in Boston, Massachusetts, told Reuters Health.
``It is my personal advice that such women should be discouraged from consuming more than two cups of coffee per day,’’ Cramer said.
The study included nearly 500 women aged 36 to 45 who were not pregnant, breast-feeding or taking hormones. All women answered questions about their diets, smoking habits, height and weight. Researchers measured the women’s hormone levels during days 1 to 5 of their menstrual cycle.
Women who consumed the most cholesterol and alcohol, and those who consumed more than one cup of coffee a day had significantly higher levels of estrogen during the early follicular phase of their menstrual cycle, according to the report in the October issue of Fertility and Sterility.
In fact, caffeine intake from all sources was linked with higher estrogen levels regardless of age, body mass index (BMI), caloric intake, smoking, and alcohol and cholesterol intake. Women who consumed at least 500 milligrams of caffeine daily, the equivalent of four or five cups of coffee, had nearly 70% more estrogen during the early follicular phase than women consuming no more than 100 mg of caffeine daily, or less than one cup of coffee.
SOURCE: Fertility and Sterility 2001;76:723-729.
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.
According to Dr. Michael Lam, a specialist in preventive and anti-aging medicine, a higher caffeine intake has a greater effect on estrogen levels. Lam notes that studies on coffee consumption and estrogen have shown that women who drink four to five cups of coffee a day, about 500mg of caffeine, had nearly 70 percent more estrogen during the early part of the menstrual cycle than women who drink less than one cup of coffee a day. Lam recommends that women limit coffee intake to one or two cups a day.
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.
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.
Robert Bock or John McGrath
NIH/National Institute of Child Health and Human Development