Study co-author Dr. Chrisandra Shufelt, assistant director of the Women's Heart Center at the Cedars-Sinai Heart Institute, said doctors long ago determined all alcohol increases the body's estrogen levels, fostering the growth of cancer cells.
The study, published online ahead of the April print edition of the Journal of Women's Health, found chemicals in the skins and seeds of red grapes slightly lowered estrogen levels while elevating testosterone among premenopausal women who drank 8 ounces of red wine nightly for about a month. The effect was not found in white wine.
The study involved 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.
Study co-author Dr. Glenn D. Braunstein said the results do not mean white wine increases the risk of breast cancer but grapes used in those varieties may lack the same protective elements found in reds.