Self-experienced physical workload and risk of breast cancer.

Objectives: The association between the risk of breast cancer and the physical load of work was studied because physical activity may reduce breast cancer risk via hormonal mechanisms.

Methods: Occupational physical activity was estimated from a self-determined rating [scale 1 (low)-5 (high)] of occupational physical load for 1800 randomly selected women born in 1930-1969. The medians of the ratings were used as occupation-specific indices of occupational physical activity.