Lifetime Occupational Physical Activity and the Risk of Breast Cancer: a Case-control Study

Objective: Epidemiological studies have shown that physical activity is a protective factor for breast cancer, although research findings are inconsistent regarding menopausal status. To determine the impact of occupational physical activity for breast cancer, a hospital-based case-control study was conducted in Poland in 2003-2007. Methods: In total, data on physical activity of 858 invasive breast cancer cases and 1,085 controls were analyzed. Odds ratios (ORs) and 95% confidence intervals (CIs) were estimated using unconditional logistic regression. Separate calculations were performed for premenopausal and postmenopausal women. Occupational physical activity was measured by sitting time and job titles. The risk estimates were controlled for potential risk factors and lifetime household and recreational activities. Results: A significantly decreased breast cancer risk was found among postmenopausal women declaring physically active jobs (requiring more than 80% of time spent standing, walking) compared with those with low activity jobs (more than 80% of the working time spent in a sitting position, during workhours) (OR=0.66; 95% CI 0.44-0.98, P trend=0.03). A similar inverse association between occupational physical activity and breast cancer risk was also found when activity was evaluated according to job titles provided by subjects. Postmenopausal women with physically demanding jobs, in particular, had a lower risk compared to those in sedentary occupations (OR=0.57; 95% CI 0.36-0.91, P trend=0.02). Conclusion: These findings support observations from previous studies that sufficiently high occupational physical activity may reduce breast cancer risk, particularly among postmenopausal women.