Burnout and sick leave due to mental disorders : heritability, comorbidity, risk factors and adverse outcomes

Common mental disorders are an increasing public health problem worldwide, and in Sweden the incidence of sick leave due to stress-related mental disorders has more than doubled since 2010. The aim of this thesis was to explore genetic and environmental aspects of burnout and sick leave due to stress-related and other mental disorders. Data from the population based Swedish Twin Registry’s questionnaire study STAGE (the Study of Twin Adults Genes and Environment) and population registers, including the MiDAS (MicroData for Analyses of the Social insurance) register, were used.

Study I was cross-sectional and included 25 378 twins that responded to STAGE. A multivariate biometric twin model was used to assess to what degree the covariation between major depressive disorder, generalized anxiety disorder, and burnout, was explained by common genetic and environmental factors in women and men. A latent common factor explained that the covariation was influenced 58% by genetics and 42% by unique environment.

Studies II-III were prospective and contained 23 611 and 11 729 STAGE responders respectively. Information from the MiDAS register was used to follow up for sick leave. In Study II logistic regression with co-twin control and a bivariate twin model was used to assess whether the associations between burnout and sick leave due to stress-related mental disorders, other mental disorders, and somatic conditions, was influenced by familial factors (genetics and shared environment). The phenotypic correlation between burnout and sick leave due to stress-related mental disorders (0.26), and between burnout and sick leave due to other mental disorders (0.30) was explained by genetic factors. The association between burnout and sick leave due to somatic conditions was modest and not influenced by familial factors. In Study III, logistic regression models were used to assess whether psychosocial work environment and health behaviors were risk factors for sick leave due to mental disorders and if the associations were influenced by familial factors. Job strain was a risk factor for sick leave due to mental disorders, after controlling for familial factors, while none of the health behaviors showed independent associations with sick leave due to mental disorders.

Study IV was register based and contained 2202 individuals on sick leave due to a mental disorder 2005-2006, according to MiDAS, and their 2202 co-twins. Cox proportional hazards regression models with co-twin control was used to investigate the short and long term effect of sick leave due to mental disorders on the outcomes reoccurring sick leave, disability pension, and unemployment, while taking familial factors into account. The risk of reoccurring sick leave was more than 3 times higher for the first two years of follow up. The risk of disability pension was 12 times higher the first year and remained almost 3 times higher throughout the rest of the follow-up time. The twice as high risk for long-term unemployment was consistent over the up to 8-year follow-up time.

In conclusion, burnout shares a genetic vulnerability with depression, anxiety, and sick leave due to mental disorders. Job strain is a risk factor for sick leave due to mental disorders regardless of familial predisposition. Sick leave due to mental disorders is a public health problem that may have serious consequences, both for individuals and to society as a whole.

List of scientific papers

I. Mather L, Blom V, Bergström G, Svedberg P. An Underlying Common Factor, Influenced by Genetics and Unique Environment, Explains the Covariation Between Major Depressive Disorder, Generalized Anxiety Disorder, and Burnout: A Swedish Twin Study. Twin Research and Human Genetics. 2016; 9(6): 619-627.
https://doi.org/10.1017/thg.2016.73

II. Mather L, Bergström G, Blom V, Svedberg P. The Covariation Between Burnout and Sick Leave Due to Mental Disorders Is Explained by a Shared Genetic Liability: A Prospective Swedish Twin Study With a Five-Year Follow-up. Twin Research and Human Genetics. 2014; 17(6): 535-44.
https://doi.org/10.1017/thg.2014.46

III. Mather L, Bergström G, Blom V, Svedberg P. High Job Demands, Job Strain, and Iso-Strain Are Risk Factors for Sick Leave due to Mental Disorders: A Prospective Swedish Twin Study With a 5-Year Follow-Up. Journal of Occupational and Environmental Medicine. 2015; 57(8): 858-65.
https://doi.org/10.1097/JOM.0000000000000504

IV. Mather L, Blom V, Bergström G, Svedberg P. Adverse outcomes of sick leave due to mental disorders: a prospective study of discordant twin pairs. Scandinavian Journal of Public Health. 2017.
https://doi.org/10.1177/1403494817735755