Physical activity and incidence of postmenopausal breast cancer

Whether physical activity reduces the risk of postmenopausal breast cancer is uncertain; few studies have addressed this issue. We examined the associ ation of leisure physical activity with breast cancer incidence among 37,10 5 postmenopausal participants in the Iowa Women's Health Study. Women repor ting the highest level of physical activity at baseline compared with women with the lowest level of activity had an age-adjusted relative risk of bre ast cancer of 0.92 (95% confidence interval = 0.80-1.05). Women reporting a ny regular leisure-time physical activity had a relative risk of 0.97 (95% confidence interval = 0.87-1.08) compared with those reporting no such regu lar physical activity. Adjustment fur potential confounders did not appreci ably alter the findings. There is little evidence from this study that phys ical activity later in life is associated to any appreciable extent with br east cancer incidence.