Physical activity levels among urban and rural women in south India and the risk of breast cancer: a case-control study.

Breast cancer (BC) incidence in India is approximately 100% higher among urban women than rural women. The role of household activities (HA) among urban and rural women in the development of BC was investigated. The study was conducted between 2002 and 2005, at the Regional Cancer Center, Trivandrum and three cancer hospitals in Chennai. Cases (735 urban and 1131 rural) were women with histologically confirmed incident BC. Controls (631 urban and 1242 rural) were age-matched women, who accompanied cancer patients to the hospital. Using in-person interview, information on time spent on HA and potential confounding variables was collected. Odds ratio (OR) and 95% confidence intervals (CI) of BC were estimated according to the time spent on HA through logistic regression models. Time spent on HA was longer among rural women (urban vs. rural: 48 vs. 59% in Trivandrum and 31 vs. 41% in Chennai for 5 or more hours/day on HA). The risk of BC declined with increasing time spent on HA. Compared with less than 3 h/day, the ORs for 5-6 h/day were 0.48 (95% CI: 0.32-0.72) in premenopausal and 0.49 (95% CI: 0.34-0.72) in postmenopausal women. Corresponding ORs for 6 or more hours/day were 0.70 (95% CI: 0.48-1.02) and 0.51 (95% CI: 0.35-0.73). The study supports the hypothesis that a high level of physical activity (PA) contributes to the difference in BC risk between urban and rural women in India. The proportion of BC avoided because of moderate or high PA was estimated to be 19% in urban women and 38% in rural women.