A major prospective study has reported that regular physical activity, whether work-related or from exercise, is associated with reduced risk of breast cancer. The influence of various types and intensities of physical activity on breast cancer risk have not been established.

The study included 73,049 Chinese women aged 40 to 70 years who had worked outside the home. Data regarding specific types of self-reported and work history-related physical activity was collected, including exercise during adolescence and adulthood, household activity, and walking or cycling for transportation. Occupational sitting time and work-related physical activity energy expenditure were estimated based on lifetime occupational histories. A total of 717 breast cancer cases were diagnosed during the study period.

Breast cancer risk was found to be almost 20% lower among women in the lowest fourth of average work-related sitting time and 27% lower in the highest fourth of average work-related energy expenditure. Exercise during adulthood at or above the recommended level of eight metabolic equivalent hours per week per year (amounting to approximately 160 minutes of fast walking per week) was associated with a 27% lower risk of breast cancer in postmenopausal women. Having both an active job and exercise participation did not confer any additional reduction in risk per se. Other common daily activities were not found to be associated with lower risk. The authors conclude that both exercise and work-related physical activity are associated with lower breast cancer risk.