Physical activity in usual occupation and risk of breast cancer (United States)

We have used data from a large population-based case-control study inthe United States to evaluate the effect of occupational physical activity onbreast cancer risk. Women diagnosed with breast cancer identified from fourstate cancer registries, and controls randomly selected from lists oflicensed drivers or Medicare beneficiaries, were interviewed by telephone forinformation on usual occupation and other factors. We classified usualoccupation into one of four categories of physical activity. After excludingsubjects for whom a strength rating could not be assigned, we had a finalsample size of 4,863 cases and 6,783 controls. Using conditional logisticregression models, we calculated adjusted odds ratios (OR) and 95 percentconfidence intervals (CI) for occupations having light, medium, and heavyactivity compared with sedentary ones. Women with heavy-activity occupationshad a lower risk of breast cancer than women with sedentary jobs (OR = 0.82,CI = 0.63-1.08), as di d women with jobs with medium activity (OR = 0.86, CI= 0.77-0.97) or light activity (OR = 0.92, CI = 0.84-1.01). There was asignificant decreasing trend in the ORs from sedentary to heavy work (P =0.007). Although limited by exposure misclassification, these data areconsistent with the hypothesis that physical activity reduces the risk ofbreast cancer.