Strenuous physical activity and breast cancer risk in African-American women

Objectives: Some studies of white women suggest that exercise reduces the i ncidence of breast cancer. There are no data on black women. We assessed th e relationship between strenuous physical activity and prevalent breast can cer among participants in the Black Women's Health Study. Methods: Data on strenuous recreational physical activity at various ages a nd other factors were collected in 1995 by mail questionnaire from 64,524 U nited States black women aged 21 to 69 years. The 704 women who reported br east cancer (cases) were matched on age and on menopausal status at the tim e of the breast cancer diagnosis with 1408 women who did not report breast cancer (controls). Odds ratios for levels of physical activity at various a ges were derived from conditional logistic regression with control for pote ntial confounding factors. Results: Odds ratios for greater than or equal to7 h per week relative to < 1 were significantly reduced for strenuous activity at age 21 for breast ca ncer overall and premenopausal breast cancer, at age 30 for breast cancer o verall, and at age 40 for postmenopausal breast cancer. There was no eviden ce of a reduction associated with exercise in high school. Conclusions: The findings of the present study suggest that strenuous physi cal activity in early adulthood is associated with a reduced risk of breast cancer in African-American women.