Joint contribution of body mass index and psychological distress to short and long sickness absence among young and early midlife public sector employees: a register-linked follow-up study.

Overweight/obesity and psychological distress often co-exist and are associated with sickness absence (SA). The objective of this study was to examine joint contribution of overweight/obesity and psychological distress on short and long SA periods, and to explore potential synergistic interactions between these factors. The Helsinki Health Study survey collected in 2017 among 19-39-year-old Finnish municipal employees was linked to employer's SA registers (1-7 days for short and 8+ days for long SA periods), including participants consenting to linkage (n = 3966, 80% women). The mean follow-up time was 2.1 years. We calculated body mass index (BMI) from weight and height and evaluated psychological distress using the emotional wellbeing subscale of RAND-36 health-related quality of life survey. Rate ratios (RRs) and their 95% confidence intervals (CIs) were calculated for SA periods using negative binomial regression models. Interaction between overweight/obesity and psychological distress was examined using the Synergy Index (S). Most participants (85%) had at least one short and over one-fourth (29%) one long SA period. Overweight/obesity (42%) and psychological distress (23%) jointly contributed to short (RR, 1.62; 95% CI, 1.44-1.82) and long (RR, 2.48; 95% CI, 2.09-2.95) SA periods, compared to those with healthy weight and no psychological distress. The interaction between overweight/obesity and psychological distress was additive for short (S = 1.11), and synergistic for long SA periods (S = 1.40). Sociodemographic factors, working conditions, and health behaviors only slightly attenuated these associations. It is important to consider co-occurrence of overweight/obesity and psychological distress in prevention of SA.