Prolonged job strain and subsequent risk of cancer in women - a longitudinal study, based on the Danish Nurse Cohort.

BACKGROUND

The role of psychological stress in cancer risk is continuously debated. Stress at work is the most common form of stress and previous studies have shown inconsistent results regarding cancer risk. In this longitudinal study, we examined the association between prolonged job strain across six years and subsequent cancer risk.

METHODS AND MATERIALS

We used data from 6571 cancer-free women from the Danish Nurse Cohort aged 45-70 years at inclusion, and self-reported questionnaires on job strain at baseline in 1993 and again in 1999. Prolonged job strain was defined as high job busyness and speed, and low control in both 1993 and 1999. Information on cancer diagnosis was obtained from the Danish Cancer Registry. Cox proportional hazards models were used to estimate hazard ratios and 95% confidence intervals for overall cancer as well as subgroups of virus immune-related, hormone-related, digestive and lung cancers according to level of prolonged job strain. The women were followed from 1 January 2000 until cancer diagnosis, emigration, death or 31 December 2013 (mean follow-up 13 years) and models were adjusted for potential confounders. Effect modification was examined according to working nightshifts and full time.

RESULTS

No significant differences in the risk of overall cancer or any of the cancer subgroups were identified in relation to prolonged busyness, speed, influence, or overall job strain. Effect modification by working full time was observed when examining job influence in relation to overall cancer risk, and by working nightshifts when examining job influence in relation to hormone related cancer risk. However, none of the associations were significant in stratified analyses.

CONCLUSION

We found no evidence of an increased risk of any cancer among women with prolonged job strain. Since a large proportion of cancer patients perceive psychological stress as a possible cause of their cancer disease, it is of importance to communicate these findings to the public.