https://doi.org/10.1177/1403494817735755 © Author(s) 2017 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/1403494817735755 journals.sagepub.com/home/sjp Scandinavian Journal of Public Health, 1–10 Introduction Mental disorders often affect people of working age, and are a leading cause of years lived with disability worldwide [1]. Mental disorders are also one of the most common reasons for work disability in Europe [2], and in Sweden mental disorders are the most common reasons for sick leave and represent the long- est sick-leave duration [3]. Mental disorders encom- passes a broad range of disorders of varying severity, however, stress-related, depressive and anxiety disor- ders are the most frequent sick-leave diagnoses [3]. In Sweden, sick leave in general is more common among women than men [3] and the sex differences are more pronounced in mental disorders, particularly in stress- related mental disorders where 74% of sickness absen- tees are women [3]. Generally, sick leave increases with age, but sick leave due to mental disorders mostly affects the age group 30–39 years [4]. Because of the high incidence, long duration and the young age of those with sick leave due to mental disorders, the indi- vidual and societal consequences could be severe, Adverse outcomes of sick leave due to mental disorders: A prospective study of discordant twin pairs LISA MATHER 1 , VICTORIA BLOM 1,2,3 , GUNNAR BERGSTRÖM 4,5 & PIA SVEDBERG 1 1 Division of Insurance Medicine, Karolinska Institutet, Sweden, 2 The Swedish School of Sport and Health Sciences, Sweden, 3 Department of Psychology, Stockholm University, Sweden, 4 Division of Intervention and Implementation Research, Karolinska Institutet, Sweden, and 5 Centre for Occupational and Environmental Medicine, Stockholm County Council, Sweden Abstract Aims: The aim of this study was to investigate whether sick leave due to different mental disorders increased the risk of reoccurring sick-leave, disability pension and unemployment, taking genetics and shared environment into account. Methods: This register-based cohort study contains 2202 discordant twin pairs 18–64 years old, where one twin had sick leave due to a mental disorder 2005–2006. The end of the sick-leave spell was the start of follow-up for both twins. The twins were followed up for reoccurring sick-leave, disability pension and unemployment (> 180 days in a year), until December 2012. Analyses were censored for disability pension, death, emigration and old-age pension. Cox proportional hazards models with time- varying covariates were used to calculate hazard ratios with 95% confidence intervals (CI). Results: Those with sick leave due to mental disorders had a 3.64 (CI: 3.24–4.08) times higher risk of reoccurring sick-leave within the first two years; after that, hazard ratios were attenuated and explained by genetic factors. The first year, they had 12.24 (CI: 8.11–18.46) times the risk of disability pension. The risk was attenuated but remained at 2.75 (CI: 2.07–3.65) after one year. The risk of unemployment was 1.99 (CI: 1.72–2.31) during the whole follow-up period. The risk of unemployment and disability pension was lower for those with stress-related than other mental disorders, this was less clear for recurrent reoccuring sick-leave. Conclusions: Sick leave due to mental disorders increased the risk of reoccurring sick-leave within two years, disability pension and unemployment, independent of genetics and shared environment. Key Words: Sick Leave, disability insurance, unemployment, twins, mental disorders Correspondence: Lisa Mather, Department of Clinical Neuroscience, Karolinska Institutet, Berzelius väg 3, SE-171 77 Stockholm, Sweden. E-mail: lisa.mather@ki.se Date received 18 January 2017; reviewed 24 August 2017; accepted 5 September 2017 735755SJP 0 0 10.1177/1403494817735755L. Mather et al.Sick leave due to mental disorders: A twin study research-article 2017 ORIGINAL ARTICLE