Caffeine changes women's estrogen levels and has different effects in Asian and Caucasian women, a recent study reveals.

Estrogen is the reproductive hormone produced primarily by the ovaries.

Study Details

More than 250 women, ages 18 to 44, took part in the BioCycle Study between 2005 and 2007. On average, they consumed 90 milligrams of caffeine a day, about the equivalent of one cup of caffeinated coffee.

The caffeine consumed by the women in the study came from any of these sources: Coffee black tea, green tea and caffeinated soda. The findings differed slightly when the researchers considered the source of caffeine individually.

Higher Levels For Asian Coffee Drinkers

Asian women who consumed an average of 200 milligrams or more of caffeine a day (equivalent to about two cups of coffee) had elevated estrogen levels compared with women who consumed less. But Caucasian women who consumed the same amount of caffeine had slightly lower estrogen levels than women who consumed less.

African American women who consumed 200 or more milligrams of caffeine daily had elevated estrogen levels, but this finding was not statistically significant, said researchers at the US National Institutes of Health.

Consuming 200 milligrams of caffeine from coffee mirrored the overall findings. But consumption of more than one cup each day of caffeinated soda or green tea was associated with higher estrogen levels in all three groups of women.

The study was published online in the American Journal of Clinical Nutrition.

Possible Long-Term Effects

The caffeine-related changes in estrogen levels did not appear to affect women's ovulation, said the researchers, who followed the women for up to two menstrual cycles.

“The results indicate that caffeine consumption among women of child-bearing age influences estrogen levels," said study coauthor Enrique Schisterman, PhD, Division of Epidemiology, Statistics and Prevention Research at the Eunice Kennedy Shriver US National Institute of Child Health and Human Development, 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," Schisterman said.

About 89% of US women ages 18 to 34 consume the caffeine equivalent of 15 to two cups of coffee a day, according to the authors.

Hysterectomy Linked to Heart Disease

Hysterectomy is linked to cardiovascular disease.

Recent finding: Women who have hysterectomies before age 50 are nearly 20% more likely to develop coronary artery disease or heart failure or have strokes than women who have not had hysterectomies.

Possible reason: Removal of the uterus disrupts blood flow to the ovaries, decreasing heart-protective estrogen. No link has been found between hysterectomy and heart disease in women over age 50.

Calcium Supplements May Increase Heart Risk

Recent finding: People who take 1,000 milligrams of calcium per day have a 25% higher risk for heart attack and 15% higher risk for stroke than people who do not take the supplements.

Possible connection: The supplements may increase the blood calcium level rapidly, contributing to arterial disease

Best: Get calcium naturally from food.

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