A prospective study of job strain and risk of breast cancer

Background. There is conflicting evidence on whether stress is a risk factor for breast cancer. The present study examined prospectively the relationship between stress at work and risk of breast cancer. Methods. Participants comprised 26 936 postmenopausal women in the Nurses' Health Study ages 46-72 who were in paid employment, and who had no previous history of cancer. Multivariate-adjusted regression analysis was used to examine the relationship between job strain (measured by the Karasek Job Content Questionnaire in 1992) and risk of incident invasive and in situ breast cancer. Results. From 1992 through 1994, 219 women were diagnosed with breast cancer. No evidence was found for a relationship between job stress and risk of breast cancer. Compared with women in low strain jobs, the multivariate-adjusted relative risks of breast cancer were RR = 0.78 (95% CI : 0.52-1.16) for high-strain jobs; RR = 0.76 (95% CI: 0.49-1.17) for active jobs; and RR = 0.94 (95% CI: 0.67-1.34) for passive jobs. Although job strain was related to less breast cancer screening among women in highly demanding jobs, it was not associated with tumour size. Conclusions. Job stress was not related to an increase in the incidence of breast cancer in the present cohort of nurses.