Influence of Occupational Stress on Breast Cancer Incidence in the Women's Health Initiative

Objective: Psychological stress has long been posited as a potential risk factor for breast cancer. We aimed to examine the relationship between occupational stress and the incidence of invasive breast cancer among postmenopausal women from the Women's Health Initiative Observational Study. Method: Occupational stress was characterized through linkage of Standard Occupational Classification codes for participants' jobs to the Occupational Information Network. Following the Karasek job strain model, we cross-categorized demand and control and created four categories of occupational strain. Cox proportional hazards regression models were used to calculate hazard ratios and 95% confidence intervals (CIs). Results: Women with a history of high-strain work (high demand and low control) compared to low-strain work (low demand and high control) were 9% more likely to develop invasive breast cancer during follow-up (hazard ratios = 1.09; 95% CI [1.00, 1.19]) when controlling for age, race/ethnicity, geographical region, education, marital status, and familial history of breast cancer. This weak association between high-strain work and risk of breast cancer was rather consistent across analyses, but CIs included the null value in most models. Conclusions: Our results highlight the potential importance of the occupational domain as a source of stress for women and suggest a possible, but yet tenuous, role in chronic disease etiology.