Evidence continues to mount that physical activity may reduce the risk of many types of cancer. Researchers at the University of Pittsburgh compared 767 women diagnosed with ovarian cancer with 1,367 matched controls. The women, aged 20 to 69, and primarily white, were asked to recall how many hours of leisure-time exercise they did during each decade of their lives, beginning with their teens. These numbers were averaged to produce a single estimate of physical activity throughout life. Walking, which can be difficult to reliably measure in a questionnaire, did not count. (When considered separately, walking had no significant affect on cancer risk.) After adjusting for age, race, body mass index, use of oral contraceptives, tubal ligation, family history of ovarian cancer, number of children and educational level—factors which may affect the risk of cancer—researchers found that women who exercised more were less likely to develop ovarian cancer. The effect of diet was not considered. Women who averaged more than six hours of activity per week over their lifetimes had a 27 percent lower risk of ovarian cancer than women who averaged less than one hour of activity per week. Women who exercised one to six hours per week reduced their risk by 15 percent. Source: Obstetrics & Gynecology, October 2000; 96, 4, 609-614