Association of physical activity during adolescence and early adulthood and risk of breast cancer before age 40 years

Breast cancer incidence is increasing in women under age 40 years, underscoring the need for research on breast cancer risk factors for younger women. Analysis in the cohort of the multinational Prospective Family Study, which is enriched with women who have a breast cancer family history, found that being in the highest versus lowest quartile of recreational physical activity (RPA) during adolescence (12-17 years) was associated with 12% lower risk of breast cancer before age 40 (HR 0.88; 95% CI 0.78-0.09), whereas being in the highest versus lowest quartile of RPA during early adulthood (25-34 years) was associated with 16% lower risk of breast cancer before age 40 (0.84; 0.74-0.95), and being in the highest versus the lowest quartile of RPA during both adolescence and early adulthood was associated with 22% lower risk of breast cancer before age 40 (0.78;0.68-0.89). The authors conclude that these findings suggest that RPA during adolescence and early adulthood may lower risk of breast cancer before age 40.