[Physical activity and breast cancer risk in Mexican women]

To evaluate the effect of moderate physical activity (hours per week and METs hours per week) on the risk of breast cancer (BC) in Mexican women.

This is the initial stage of a case control multicentric study based in the Federal District, Monterrey and Veracruz, Mexico, during 2004. Fifty eight cases paired to 58 control cases on quinquennium of age, and belonging to the health system were analyzed: three hospitals from the IMSS, three from ISSSTE and three from SS participated.

In postmenopausal women, there was a reduction of the risk in BC by every additional hour per week of moderate physical activity (RM= 0.91; IC95% 0.85-0.97); in premenopausal women, the reduction of the risk was not statistically significant (RM= 0.99; IC95% 0.94-1.05) (p= 0.048, effect modification).

Moderate physical activity reduces the risk of BC in postmenopausal Mexican women.