Moderate physical activity in relation to mammographic patterns

High-risk mammographic patterns may be used as a surrogate end point for br east cancer in etiologic research as well as in prevention studies. Physica l activity may be one of the few modifiable risk factors for breast cancer. We examined the relationship between physical activity and mammographic pa tterns among 2720 Norwegian women, ages 40-56 years, who participated in bo th the Second and Third Tromso studies. Epidemiologic data were obtained th rough questionnaires. Two questions from the Second Tromso study and five q uestions from the Third elicited information on physical activity. The mamm ograms were categorized into five groups based on anatomical-mammographic c orrelations. For analysis, patterns I through III were combined into a low- risk group and patterns IV and V into a high-risk group. Odds ratios that w ere adjusted for age, education, menopausal status, body mass index, parity , age at menarche, oral contraceptive use, and alcohol intake, with 95% con fidence intervals, were estimated using logistic regression. Women who repo rted moderate physical activity, i.e., more than 2 h/week, were 20% less li kely (odds ratio, 0.8; 95% confidence interval, 0.6-1.1) to have high-risk mammographic patterns compared with those who reported being inactive. This relationship remains consistent when stratified by menopausal status, pari ty, and tertiles of body mass index. However, all of the associations betwe en various measures of physical activity and high-risk patterns found in th is study are weak with confidence intervals that include 1.0. Thus, chance is a reasonable explanation for the weak associations found. The relationsh ip between physical activity and high-risk patterns should be examined furt her as a means to explore the biologic mechanisms relating physical activit y to breast cancer risk.