Night work as a risk factor for future cause-specific disability pension: A prospective twin cohort study in Sweden.

The objectives of the study were to investigate the associations between night work and disability pension (DP) due to all causes, cardiovascular (CVD), mental, and other diagnoses, adjusting for familial confounding. The material of the study included comprehensive survey data on 27 165 Swedish twins born in 1935-1958 that were linked with DP data for the survey period (1998-2003) to 2013. Night work was assessed as years of working nights at least every now and then, and categorized into not at all, 1-10 years and over 10 years. For statistical analyses, Cox proportional hazards regressions were used to calculate hazard ratios (HRs) with 95% confidence intervals (CIs). The results of the study indicated that over 10 years duration of night work had an age- and sex-adjusted HR of 1.48 (95% CI 1.11-1.98) for DP due to CVD and 1-10 years of night work an HR of 1.28 (95% CI 1.06-1.55) for DP due to mental diagnoses, but attenuated when covariates were adjusted for. Both 1-10 years (HR 1.27, 95% CI 1.17-1.39) and >10 years of night work (HR 1.20, 95% CI 1.08-1.34) were associated with DP due to all causes and other diagnoses. These risks remained after adjusting for covariates. To conclude, even modest exposure in terms of duration of night work is a risk factor for all-cause DP, but also for DP due to mental and other diagnoses. The risk of DP due to CVD seems to be associated with longer (>10 years) periods of night work. All the associations between night work and DP seem to be influenced by various covariates.