Drinking red wine in moderation may reduce one of the risk factors for breast cancer, providing a natural weapon to combat a major cause of death among U.S. women, new research from Cedars-Sinai Medical Center shows.

The study, published online in the Journal of Women's Health, challenges the widely held belief that all types of alcohol consumption heighten the risk of developing breast cancer. Doctors long have determined that alcohol increases the body's estrogen levels, fostering the growth of cancer cells.

But the Cedars-Sinai study found that chemicals in the skins and seeds of red grapes slightly lowered estrogen levels while elevating testosterone among premenopausal women who drank eight ounces of red wine nightly for about a month.

White wine lacked the same effect.

Researchers called their findings encouraging, saying women who occasionally drink alcohol might want to reassess their choices.

"If you were to have a glass of wine with dinner, you may want to consider a glass of red," said Chrisandra Shufelt, M.D., assistant director of the Women's Heart Center at the Cedars-Sinai Heart Institute and one of the study's co-authors. "Switching may shift your risk."

In the Cedars-Sinai study, 36 women were randomized to drink either Cabernet Sauvignon or Chardonnay daily for almost a month, then switched to the other type of wine. Blood was collected twice each month to measure hormone levels.

Researchers sought to determine whether red wine mimics the effects of aromatase inhibitors, which play a key role in managing estrogen levels. Aromatase inhibitors are currently used to treat breast cancer.

Investigators said the change in hormone patterns suggested that red wine may stem the growth of cancer cells, as has been shown in test tube studies.

Co-author Glenn D. Braunstein, M.D., said the results do not mean that white wine increases the risk of breast cancer but that grapes used in those varieties may lack the same protective elements found in reds.

"There are chemicals in red grape skin and red grape seeds that are not found in white grapes that may decrease breast cancer risk," said Braunstein, vice president for Clinical Innovation and the James R. Klinenberg, M.D., Chair in Medicine.

The study will be published in the April print edition of the Journal of Women's Health, but Braunstein noted that large-scale studies still are needed to evaluate the safety and effectiveness of red wine to see if it specifically alters breast cancer risk. He cautioned that recent epidemiological data indicated that even moderate amounts of alcohol intake may generally increase the risk of breast cancer in women. Until larger studies are done, he said, he would not recommend that a non-drinker begin to drink red wine.

The research team also included C. Noel Bairey Merz, M.D., director of the Women's Heart Center, director of the Preventive and Rehabilitative Cardiac Center and the Women's Guild Chair in Women's Health, as well as researchers from the University of Southern California Keck School of Medicine and Hartford Hospital in Connecticut.