Intensity of lifetime physical activity and breast cancer risk among Polish women.

Physical activity is associated with a lower risk of breast cancer, although research findings are inconsistent regarding the type, duration, intensity, and frequency of activities that are necessary to reduce the risk, as well as dependence on menopausal status. To address these issues, I examined the effect of physical activity on breast cancer risk among 858 Polish invasive breast cancer cases and 1085 controls. Data on components of lifetime household, occupational, and recreational activities were collected in 2003-2007, using a self-administered questionnaire. Odds ratios with 95% confidence intervals were estimated using unconditional logistic regression analyses and a full assessment of confounding variables. For all types of physical activity, odds ratios were calculated for self-reported and compendium-based assigned levels of activity. Moderate- and vigorous-intensity total and recreational activities, as well as moderate- and long-lasting low-intensity household activities, lowered the risk by at least 44% for the highest versus lowest quartiles of activity in both menopausal groups. The associations were linear (P(trend) < or = 0.009). There was a suggestion of a risk reduction for occupational activity among post-menopausal women. These findings show that a risk reduction can be achieved by vigorous-intensity activities or by longer-lasting activities of moderate-intensity.