BEIJING, May 23 (Xinhuanet) -- Women who gain weight in adulthood face a higher lifetime risk of all types of breast cancer, according to a new study by the American Cancer Society (ASC) Monday.

    A study of more than 44,000 women found that the more weight a woman gained, the greater her risk for all types, stages, and grades of breast cancer.

    Compared to women who gained 20 pounds (10 kg) or less during adulthood, women who gained more than 60 pounds (27 kg) were almost twice as likely to have ductal type breast tumors and more than 1.5 times more likely to have lobular type cancers, Heather Spencer Feigelson of the society and colleagues found.

    The risk of breast cancer tripled for women who gained more than 60 pounds (27 kg).

    Breast cancer risk is linked to increased levels of the hormone estrogen and fat tissue produces estrogen, adding to the risk.

    There are many other theories to explain the effect of weight gain on breast cancer. According to the estrogen theory, with fat tissue the primary source of estrogen, the hormone levels in postmenopausal women are 50 to 100 percent higher among heavy women than lean women. Estrogen-sensitive tissues are therefore exposed to more estrogen stimulation in obese women, leading to a more rapid growth of estrogen-responsive breast cancer.

    The distribution of body fat may also affect breast cancer risk, previous studies have found. Women with a large amount of abdominal fat have a greater breast cancer risk than those whose fat is distributed over the hips, buttocks, and lower extremities.

    An estimated 64 percent of U.S. adults are either overweight or obese, according to the 1999-2000 National Health and Nutrition Examination Survey (NHANES). Obesity is believed to be responsible for 3.2 percent of all new beast cancer cases diagnosed each year. Enditem

(Agencies)