Study Finds Alcohol Use Raises Breast Cancer Risk : Health: Researchers say two drinks a day increase levels of the hormone estrogen, which has been linked to tumors.

Two alcoholic drinks a day are enough to raise hormone levels in women and put them at greater risk of developing breast cancer, according to a study at the National Institutes of Health.

The research provides a possible explanation for the fact that other studies have shown an increase of breast cancer among women who drink, said Marsha E. Reichman, who did the research while at the National Cancer Institute.

Diet and disease research over the last 10 years have shown that women who drink moderately have a breast cancer risk that is 40% to 100% greater than women who do not drink. Other studies have associated estrogen, a hormone, with breast cancer.

Reichman said the new study is the first to provide a link between the earlier findings.

“This is the first study to suggest that the mechanism by which alcohol affects breast cancer risk may be the increase in hormones caused by alcohol,” she said.

A report on the study is to be published today in the Journal of the National Cancer Institute.

In the study, 34 women were divided into two groups and tested for effects of alcohol through six menstrual cycles. Throughout the study, the women were on controlled diets so that the only dietary difference was the alcohol. Blood and urine tests were taken for three days during three phases of the menstrual cycle.

For half of the study, one group of women was given nightly 30 grams of pure grain alcohol mixed in orange juice. The other group was given orange juice without the alcohol. For the second half of the study, the groups reversed their alcohol use. In this way, both halves of the study group received the alcohol dose for three menstrual cycles.

Blood tests showed increases in estrogen of up to 31.9% during the middle phase of the menstrual cycle, the peri-ovulatory phase, for women who were drinking. Urine tests showed a similar increase in estrogen excreted during the luteal, or final, phase of the menstrual cycle for those on alcohol. Little change was found in the early, or follicular, part of the cycle.

Joseph T. Judd, a scientist at the Beltsville Human Nutrition Research Center of the Department of Agriculture, said that the alcohol was 200 proof. He said 30 grams of the beverage is approximately equal to the amount of alcohol used in two “very strong” mixed drinks, such as martinis.