Genetic and environmental contributions to long-term sick leave and disability pension: a population-based study of young adult Norwegian twins

Genetic and environmental contributions to individual differences in sustainable working life-A Swedish twin cohort study

Although genetics is known to have a role in sickness absences (SA), disability pensions (DP) and in their mutual associations, the empirical knowledge is scarce on not having these interruptions, i.e., sustainable working life. Hence, we aimed to investigate how genetic and environmental factors affect individual variation in sustainable working life in short-term (two consecutive years) and in long-term (22 years of follow-up) using the classical twin modeling based on different genetic relatedness of mono- and dizygotic twins. The final sample (n = 51 071) included Swedish same-sex twins with known zygosity born between 1930 and 1990 (53% women) with complete national register data of employment, SA, DP, unemployment, old-age pension, emigration, and death. For the short-term sustainable working life, genetic factors explained 36% (95% confidence intervals (CI) 31-41%), environmental factors shared by co-twins such as family background 8% (95% CI 5-14%) and environmental factors unique to each twin individual 56% (95% CI 56-56%) on the individual differences. For the long-term sustainable working life, the largest proportions on individual differences were explained by environmental factors shared by co-twins (46%, 95% CI 44-48%) and unique to each twin individual (37% 95% CI 36-38%) whereas a small proportion was explained by genetic factors (18%, 95%CI 14-22%). To conclude, short-term sustainable working life was explained to a large extent by unique environment and to lesser extent by genetic factors whereas long-term (22 years) sustainable working life had both moderate unique and common environmental effect, and to lower extent genetic effects contributing to individual differences. These findings suggest that sustainable working life have different short- and long-term predictors.

Sickness absence transitions among Swedish twins with back, neck or shoulder pain and common mental disorders applying a multi-state approach

We aimed to investigate transitions to and from sickness absence, or disability pension among individuals with back, neck, or shoulder pain and/or with common mental disorders (CMDs), and the role of familial (genetics and shared environment) influences on the transitions. Swedish twins born 1935-1985 who responded to pain and CMDs survey items (N = 41,516) were followed on average 8.7 years for sickness absence states in national registers. Multi-state Cox regression models were applied for three exposure groups: pain, CMDs, and presence of both, compared to unexposed. Exposure discordant twin pairs, stratified by zygosity, were analysed to assess the role of familial factors. Hazard Ratios (HR) with 95% confidence intervals and transition intensities were calculated. HRs were similar for transitions between states among those with pain or CMDs. The highest HRs were for transitions from entry to sickness absence and sickness absence to disability pension among those with both pain and CMDs (HRs: 1.61 and 1.43, respectively). Higher HRs for dizygotic compared to monozygotic twins for the first transition to sickness absence and for altering back to not being sickness absent indicate familial confounding. Back, neck, or shoulder pain and/or CMDs indicate a higher risk to become sickness absent and for repeated sickness absence episodes over time compared to unaffected.

Associations of Internalizing and Externalizing Problems in Childhood and Adolescence With Adult Labor Market Marginalization

Importance

Mental health problems in early life are associated with labor market marginalization, especially in youths with persistent internalizing and externalizing problems. However, previous research has not adjusted for familial (genetic and shared environmental) factors.

Objective

To examine associations of early-life internalizing and externalizing problems with adulthood unemployment and work disability, adjusting for familial factors.

Design, Setting, and Participants

This population-based prospective cohort study included Swedish twins who were born in 1985-1986 and surveyed at 4 consecutive waves across childhood and adolescence until 2005. Through linkage to nationwide registries, participants were followed up from 2006 to 2018. Data analyses were conducted between September 2022 and April 2023.

Exposures

Internalizing and externalizing problems, assessed with the Child Behavior Checklist. Participants were differentiated regarding duration of internalizing and externalizing problems (persistent, episodic, and noncases).

Main Outcomes and Measures

Unemployment (180 days or more of being unemployed) and work disability (60 days or more of being sickness absent or disability pensioned) during follow-up. Cox proportional hazards regression models were calculated to obtain cause-specific hazard ratios (HRs) with 95% CIs in the whole cohort and exposure-discordant twin pairs.

Results

Of 2845 participants, 1464 (51.5%) were female. Incident unemployment was experienced by 944 (33.2%) and incident work disability by 522 (18.3%) participants. Compared with noncases, persistent internalizing problems were associated with unemployment (HR, 1.56; 95% CI, 1.27-1.92) and work disability (HR, 2.32; 95% CI, 1.80-2.99). Similarly, compared with noncases, persistent externalizing problems were associated with unemployment (HR, 1.87; 95% CI, 1.55-2.26) and work disability (HR, 2.38; 95% CI, 1.87-3.03). Persistent cases had overall higher risks of adverse outcomes than episodic cases. After adjustment for familial factors, associations with unemployment were no longer statistically significant, whereas associations with work disability remained or were only slightly reduced.

Conclusions and Relevance

In this cohort study of young Swedish twins, familial factors explained the associations between early-life persistent internalizing and externalizing problems and unemployment; such factors were comparatively less important for the association with work disability. This suggests nonshared environmental factors may be important for the risk of future work disability among young individuals with persistent internalizing and externalizing problems.

Sickness absence among young employees in private and public sectors with a history of depression and anxiety

The aim was to investigate occurrence and duration of sickness absence (SA) among young employees with previous depression/anxiety in private and public sectors. This population-based prospective study included 11,519 Swedish twin individuals of age 19-29 years that were followed regarding SA during 2006-2016. Data on previous depression/anxiety came from two screening surveys in 2005. Data on SA and employment sector were received from national registries. Descriptive statistics and logistic regression were used, also controlling for familial factors. Proportion of employees with SA was significantly higher among those with, as compared to those without, previous depression/anxiety, regardless the employment sector. Individuals with previous depression/anxiety had increased risk for future SA, in both private (OR 2.25, 95% CI 1.90-2.66) and public sectors (OR 2.10, 95% CI 1.73-2.54). Familial factors played a role in the association among employees in the private sector. A higher proportion of long-term SA was observed among employees with previous depression/anxiety in the private as compared to the public sector. To conclude, previous depression/anxiety tends to increase risk for SA among young employees in both employment sectors, whereas long-term SA seemed to be more prevalent among those in the private as compared to the public sector.

Sustainable Working Life Patterns in a Swedish Twin Cohort: Age-Related Sequences of Sickness Absence, Disability Pension, Unemployment, and Premature Death during Working Life

We aimed to investigate sustainable working life via age-related sequences of sickness absence (SA), disability pension (DP), unemployment (UE), premature death, and the influence of individual characteristics, accounting for familial confounding. The sample included monozygotic (MZ) and dizygotic (DZ) same-sexed twin pairs with register data (n = 47,450) that were followed for 10 years in four age cohorts: 26-35 (n = 9892), 36-45 (n = 10,620), 46-55 (n = 12,964) and 56-65 (n = 13,974). A sequence analysis was done in a 7-element state space: 1. "Sustainable working life": SA/DP 0-30 days and UE 0-90 days; 2. "Unemployment >90 days": SA/DP 0-30 days and UE > 90 days; 3. "Moderate SA/DP": SA/DP 30-180 days; 4. "Almost full year of SA/DP": SA/DP 180-365 days; 5. "Full year of SA/DP": SA/DP ≥ 365 days; 6. Death; 7. Old-age pension. The largest cluster had a sustainable working life and never experienced states 2-6 (34-59%). Higher education and being married predicted a lower likelihood of experiencing states 2-6. The MZ twin pairs (vs. DZ) were more often in the same cluster suggesting the role of genetic factors. To conclude, the sustainable working life was the largest cluster group. Few individuals had prolonged periods of interruptions of sustainable working life meriting actions, especially in early adulthood for interventions to support workability.

Effects of age on psychosocial working conditions and future labour market marginalisation: a cohort study of 56,867 Swedish twins

PURPOSE

Previous studies have reported an elevated risk of sickness absence (SA) and disability pension (DP) due to adverse psychosocial working conditions, yet the influence of age and familial factors on the associations have not been examined. We aimed to investigate associations between psychosocial working conditions and labour market marginalisation (LMM) in terms of unemployment, SA and DP adjusting for familial confounding and possible differences in these associations with different age groups and different unemployment and sick leave days.

METHODS

All twins living in Sweden in 2001, aged 16-64 years and not on old-age pension or DP were included (n = 56,867). The twins were followed from 2002 to 2016 regarding unemployment, SA and DP. Cox proportional hazards regression models were performed for the whole sample, and for discordant twin pairs, in five age groups.

RESULTS

Each one-unit increase in job demands and job control was associated with a lower risk of unemployment, SA and DP in all age groups. Moreover, each one-unit increase in social support was associated with an increased risk of 1-30 days unemployment in individuals older than 45 years and SA and DP. Social support decreased the risk of unemployment longer than 365 days in age groups 16-25 and 36-45 years. In the discordant twin pair analyses, the estimates attenuated towards statistical non-significance.

CONCLUSION

Even though familial factors seem to influence the associations between psychosocial working conditions and LMM, improving psychosocial working conditions by for example promoting high job control and social support at workplace may reduce the risk of future short- and long-term LMM in all age groups.

Sustainable Working Life in a Swedish Twin Cohort-A Definition Paper with Sample Overview

Background: A unified or consensus definition of “sustainable working life” remains lacking, although studies investigating risk factors for labour market exit are numerous. In this study, we aimed (1) to update the information and to explore a definition of “sustainable working life” via a systematic literature review and (2) to describe the working life trajectories via the prevalence of sickness absence (SA), disability pension (DP), and unemployment in a Swedish twin cohort to provide a sample overview in our Sustainable Working Life-project. Methods: A systematic literature review was conducted to explore the studies with the search phrase “sustainable working life” in PubMed, PsycInfo, and the Web of Science Database of Social Sciences in January 2021, resulting in a total of 51 references. A qualitative synthesis was performed for the definitions and the measures of “sustainable working life.” Based on the Swedish Twin project Of Disability pension and Sickness absence (STODS), the current dataset to address sustainable working life includes 108 280 twin individuals born between 1925 and 1990. Comprehensive register data until 2016 for unemployment, SA and DP were linked to all individuals. Using STODS, we analysed the annual prevalence of SA, DP, and unemployment as working life trajectories over time across education and age groups. Results: The reviewed 16 full articles described several distinct definitions for sustainable working life between 2007 and 2020 from various perspectives, i.e., considering workplaces or employees, the individual, organizational or enterprise level, and the society level. The definition of “sustainable working life” appearing most often was the swAge-model including a broad range of factors, e.g., health, physical/mental/psychosocial work environment, work motivation/satisfaction, and the family situation and leisure activities. Our dataset comprised of 81%–94% of individuals who did not meet SA, DP, or unemployment during the follow-up in 1994–2016, being indicative for “sustainable working life.” The annual prevalence across years had a decreasing trend of unemployment over time, whereas the prevalence of SA had more variation, with DP being rather stable. Both unemployment and DP had the highest prevalence among those with a lower level of education, whereas in SA, the differences in prevalence between education levels were minor. Unemployment was highest across the years in the youngest age group (18–27 years), the age group differences for SA were minor, and for DP, the oldest age group (58–65 years) had the highest prevalence. Conclusions: No consensus exists for a “sustainable working life,” hence meriting further studies, and we intend to contribute by utilising the STODS database for the Sustainable Working Life project. In the upcoming studies, the existing knowledge of available definitions and frameworks will be utilised. The dataset containing both register data and self-reports enables detailed follow-up for labour market participation for sustainable working life.

The predictive role of sickness absence spell durations in associations with inpatient- and specialized outpatient care among a population-based Swedish twin sample

BACKGROUND

The associations between a sickness absence spell duration and patient care have been rarely studied. An assumption is that associations would differ by spell duration and by the patient care type, inpatient- or specialized outpatient, due to severity of diseases and/or conditions. We aimed to investigate sickness absence spells in various spell durations as a predictor for subsequent inpatient- and specialized outpatient care separately, and to study if familial confounding plays a role in these associations.

METHODS

We followed a population-based sample of Swedish twins born 1925-90 with national registers from 2001 for first incident sickness absence spell (days to calculate spell duration categorized into ≤30 days, 31-90 days, 91-180 days and ≥ 181 days), or no sickness absence, and for inpatient- and specialized outpatient care until 2013 (n = 24,975). Cox proportional hazards models were applied for hazard ratios (HR) with 95% confidence intervals (CI) while accounting for covariates and familial confounding.

RESULTS

First incident sickness absence spell across all duration categories was associated with an increased risk of inpatient- (age- and sex adjusted HR 1.28 to 6.05) or specialized outpatient care (HR 1.17-2.50), both in comparison to those without any sickness absence or the shortest sickness absence spell category (1-30 days). The associations remained statistically significant while controlling for covariates or familial confounding.

CONCLUSIONS

First incident sickness absence spell increases the risk of inpatient care or specialized outpatient care regardless of the duration of the sickness absence spell. Hence, incident sickness absence spells should be noted and targeted to actions at workplaces as well as in primary and occupational health care.

Health behaviours and psychosocial working conditions as predictors of disability pension due to different diagnoses: a population-based study

BACKGROUND

To investigate whether the clustering of different health behaviours (i.e. physical activity, tobacco use and alcohol consumption) influences the associations between psychosocial working conditions and disability pension due to different diagnoses.

METHODS

A population-based sample of 24,987 Swedish twins born before 1958 were followed from national registers for disability pension until 2013. Baseline survey data in 1998-2003 were used to assess health behaviours and psychosocial Job Exposure Matrix for job control, job demands and social support. Cox proportional hazards models were used to calculate hazard ratios (HR) with 95% confidence intervals (CI).

RESULTS

During follow-up, 1252 disability pensions due to musculoskeletal disorders (5%), 601 due to mental diagnoses (2%) and 1162 due to other diagnoses (5%) occurred. In the models controlling for covariates, each one-unit increase in job demands was associated with higher (HR 1.16, 95%CI 1.01-1.33) and in job control with lower (HR 0.87, 95%CI 0.80-0.94) risk of disability pension due to musculoskeletal disorders among those with unhealthy behaviours. Among those with healthy behaviours, one-unit increase of social support was associated with a higher risk of disability pension due to mental and due to other diagnoses (HRs 1.29-1.30, 95%CI 1.04-1.63).

CONCLUSIONS

Job control and job demands were associated with the risk of disability pension due to musculoskeletal disorders only among those with unhealthy behaviours. Social support was a risk factor for disability pension due to mental or other diagnoses among those with healthy behaviours. Workplaces and occupational health care should acknowledge these simultaneous circumstances in order to prevent disability pension.

Sick leave due to back pain, common mental disorders and disability pension: Common genetic liability

BACKGROUND

Back pain and common mental disorders are often comorbid and known risk factors for future disability pension. However, the reason for the covariation is not known. The aim was to investigate the common genetic and environmental influences on the covariation between sick leave due to back pain, sick leave due to common mental disorders and disability pension.

METHODS

Register data from the Swedish Social Insurance Agency on sick leave due to back pain, common mental disorders and disability pension between 2005 and 2018, in a population-based sample of 56,686 working age twins was used to construct biometric twin models to calculate if the covariation between the traits were due to Additive (A) or Dominant (D) genetic factors, Common environmental factors (C) or unique Environmental factors (E), for women and men.

RESULTS

The phenotypic correlations ranged between 0.17 and 0.25. A common factor common pathway AE model fitted best for both women and men. The latent underlying common factor, that explained the covariation was mostly explained by genetic factors (87% for women and 90% for men). Each trait was also influenced by its own unique genetic and unique environment factors. A higher heritability was found for disability pension than for sick leave.

CONCLUSIONS

The covariation between sick leave due to back pain and common mental disorders, and disability pension were mostly explained by common genetic factors, while the unique variation in each trait was influenced by both genetic and environmental factors not shared within the twin pairs.

SIGNIFICANCE

A common genetic liability seems to be of importance in the comorbidity of sick leave due to back pain and common mental disorders and the transition to disability pension, both among women and men. However, the proportion in each trait that was explained by genetic factors was somewhat higher for men than for women in all traits. This may be of importance to consider in intervention or prevention efforts.

Suicide attempt following sickness absence and disability pension due to common mental disorders: a prospective Swedish twin study

PURPOSE

The aim of this study was to investigate if sickness absence and disability pension (SA/DP) in general and due to specific common mental disorders (CMDs) are associated with subsequent suicide attempt among women and men by taking familial factors (genetics and shared environment) into consideration.

METHODS

This register-based cohort study includes 4871 twin pairs 18-65 years of age discordant for SA/DP due to CMDs 2005-2010. Twins were followed up for suicide attempt from inpatient and specialised outpatient care until December 2012. Conditional Cox proportional hazards regression models, adjusting for familial factors, were used to calculate hazard ratios (HR) with 95% confidence intervals (CI).

RESULTS

SA/DP due to CMDs was associated with a higher risk of suicide attempt (HR 3.14, CI 2.51-3.93). The risk of suicide attempt was five times higher among men and three times higher among women, compared to the SA/DP unaffected co-twins. In the diagnosis-specific analysis, SA/DP due to anxiety disorders resulted in the highest HR (4.09, CI 2.37-7.06) for suicide attempt, followed by depressive disorders (HR 3.70, CI 2.66-5.14) and stress-related disorders (HR 1.96, CI 1.35-2.84). The stratified analysis on zygosity indicates that there seems to be a genetic influence on the associations between SA/DP due to CMDs and suicide attempt, particularly among women and among those with SA/DP due to depressive disorders.

CONCLUSIONS

SA/DP due to CMDs was a risk factor for suicide attempt among women and men. Genetic factors might explain part of the associations for women and for those with SA/DP due to depressive disorders.

Health, work and demographic factors associated with a lower risk of work disability and unemployment in employees with lower back, neck and shoulder pain

Background

Chronic musculoskeletal pain affects over 20% of the adult population and is one of the most common reasons for sick leave in Sweden. The aim of this study was to investigate which demographic, health and psychosocial work environment factors are of importance for a lower risk of future work disability and unemployment among workers with low back pain (LBP) and/or neck shoulder pain (NSP), and if familial factors influence these associations.

Methods

All 5556 persons that reported having LBP and/or NSP in a web-based questionnaire study in 2004–2006 were included. They were followed up for work disability (sick leave > 90 days or disability pension), and unemployment (> 180 days in a year) until 31 December 2013. Hazard ratios (HR) with 95% confidence intervals were calculated using cox proportional hazard models of the whole sample, adjusting for covariates. In addition, co-twin analyses of outcome discordant twin pairs were conducted to assess the impact of familial confounding on the associations.

Results

Being male, 19–28 years old, having higher education, only NSP, no history of depression or anxiety, good self-rated health, low job demands and high job control were associated with a lower risk of work disability (adjusted HR ranging between 0.29–0.85). No history of anxiety and depression and high job control was associated with a lower risk of unemployment (adjusted HR ranging from 0.53 and 0.67). Familial factors were found to affect the association between education and work disability, but none of the other associations investigated.

Conclusions

Among those with LBP or NSP, good health in terms of mental- and self-rated health, few pain sites, as well as good psychosocial working conditions seem to indicate a lower risk for work disability.

A Life Course Study of Genetic and Environmental Influences on Work Incapacity

Work incapacity is a major public health challenge and an economic burden to both society and individuals. Understanding the underlying causes is becoming ever more relevant as many countries face an aging workforce. We examined stability and change in genetic and environmental factors influencing work incapacity from age 18 until retirement, and sex differences in these effects. The large population-based sample comprised information from 28,759 twins followed for up to 23 years combined with high-quality national registry data. We measured work incapacity as the total proportion of potential workdays lost due to sickness absence, rehabilitation and disability benefits. Structural equation modeling with twin data indicated moderate genetic influences on work incapacity throughout life in both men and women, with a high degree of genetic stability from young to old adulthood. Environmental influences were mainly age-specific. Our results indicate that largely the same genetic factors influence individual differences in work incapacity throughout young, middle and older adulthood, despite major differences in degree of work incapacity and probable underlying medical causes.

The association between part-time and temporary employment and sickness absence: a prospective Swedish twin study

Background

Sickness absence (SA) is becoming a major economic problem in many countries. Our aim was to investigate whether type of employment, including temporary employment or part-time employment, is associated with SA while controlling for familial factors (genetic and shared environment). Differences between men and women and across employment sectors were explored.

Methods

This is a prospective twin study based on 21 105 twins born in Sweden 1959–85. The participants completed a survey in 2005 with follow-up of SA (≥15 days), using register data, until end of 2013. The data were analyzed with logistic regression, with results presented as odds ratios (OR) with 95% confidence intervals (CI).

Results

Temporary employment involved higher odds of SA (OR=1.21 95% CI=1.04–1.40) compared to full-time employment. Both part-time workers (OR=0.84 95% CI=0.74–0.95) and the self-employed (OR=0.77 95%CI=0.62–0.94) had lower odds of SA. Stratifying by sex showed lower odds for part-timers (OR=0.82 95% CI=0.73–0.94) and self-employed women (OR=0.65 95% CI=0.47–0.90), but higher odds for men in temporary employment (OR=1.33 95% CI=1.03–1.72). Temporary employees in county councils (OR=1.73 95% CI=1.01–2.99) and municipalities (OR=1.41 95% CI=1.02–1.96) had higher odds while part-timers employed in the private sector had lower odds (OR=0.77 95% CI=0.64–0.93). Familial factors did not confound the association between employment type and SA.

Conclusions

Employment type is associated with SA, with temporary employment involving a higher risk compared to permanent full-time employment while both part-time employment and self-employment involved a lower risk. The associations vary between women and men and across sectors.

Time pressure and sleep problems due to thoughts about work as risk factors for future sickness absence

Purpose

This study investigated whether time pressure or sleep problems due to thoughts about work are associated with future sickness absence (SA) among women and men employed in different sectors, also when adjusting for confounders including familial factors (genetics and shared environment).

Methods

The study sample included 16,127 twin individuals (52% women), aged 19–47 years who in 2005 participated in an online survey including questions regarding time pressure, sleep, work and health. Register data on SA (> 14 days) were obtained from the National Social Insurance Agency and individuals were followed from date of survey response until 12/31/2013. Associations between time pressure, sleep problems due to thoughts about work and future SA were investigated using logistic regression analyses to assess odds ratios (OR) with 95% confidence intervals (CI).

Results

In total 5723 (35%) individuals had an incident SA spell during follow-up. Sleep problems due to thoughts about work were associated with SA in the fully adjusted model (OR 1.22, CI 1.10–1.36). Stratified by sector, the highest estimate was found for state employees (OR 1.54, CI 1.11–2.13). Familial factors did not seem to influence the associations. We found no statistically significant associations between time pressure and SA. No sex differences were found.

Conclusions

Results indicated that sleep problems due to thoughts about work is a risk factor for future SA. This follows previous research showing that sleep length and sleep disturbances, regardless of reason, are associated with SA. But, experiences of work-related time pressure seem to have no effect on SA.

Disability retirement among university public servants: epidemiological profile and causes

OBJECTIVE

To identify the epidemiological profile and causes of disability pensions for university public servants.

METHOD

A cross-sectional and descriptive study, carried out with 40 retired employees due to disability of a public university. Sociodemographic, occupational and clinical data were obtained. The analyses were stratified according to gender, considering a significance level of 5%.

RESULTS

Disability pensions were more frequent among women (72.5%), aged up to 60 years (77.5%). Mental and behavioral disorders were mainly responsible for pensions (35%). There was a significant difference between the sexes (p ≤ 0.05) for the variables: educational level, function performed by the worker and presence of dependents.

CONCLUSION

The epidemiological profile showed a higher frequency of female, married/stable marital status, aged between 51 and 60 years and up to 12 years of schooling. Chronic degenerative diseases were predominant among the causes for disability pensions.

Adverse outcomes of sick leave due to mental disorders: A prospective study of discordant twin pairs

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.

Pre-pregnancy mental distress and musculoskeletal pain and sickness absence during pregnancy - a twin cohort study

Background

Sickness absence (SA) among pregnant women is high. The aim of this study was to examine whether factors known to predict SA in general also predict SA during pregnancy by estimating the association between prior mental distress and musculoskeletal pain and SA during pregnancy, and to assess the influence of familial (genetic and shared environmental) factors. In this prospective cohort study, data from 2076 female twins born 1967-79 who participated in a questionnaire study in 1998 were linked to register data on SA and childbirth during the years 1998-2008. Baseline measures included mental distress (symptoms of anxiety and depression; SCL-5) and musculoskeletal pain (lumbar spine, neck/shoulder and/or persisting muscular pain). SA was measured as a ratio of days on SA divided by potential working days. Negative binomial regression was performed for individual and within-pair effects. Musculoskeletal pain, but not mental distress, was prospectively associated with overall SA during pregnancy in the adjusted individual-level analyses. With each standard deviation increase in musculoskeletal pain, SA granted for any disorder increased with 12% (IRR 1.12, 95% CI = 1.07-1.17) and SA granted for pregnancy related disorders increased with 9% (IRR 1.09, 95% CI = 1.02-1.17). Within-pair estimates were similar, suggesting little or no familial confounding. Women with previous musculoskeletal pain are at increased risk of SA during pregnancy, whereas no increased risk in women with previous symptoms of mental distress could be demonstrated. SA during pregnancy seems partly to be associated with different factors than SA in general.

Internalizing and externalizing problems in childhood and adolescence as predictors of work incapacity in young adulthood

BACKGROUND

There is limited information regarding the association between youth mental health problems and work incapacity in adulthood. We investigated whether internalizing (depressive, anxious, somatic complaints) and externalizing (aggressive, rule-breaking) behavior problems in childhood and adolescence were associated with sickness absence (SA) and disability pension (DP) in young adulthood.

METHODS

Data were used from the population-based and prospective Twin Study of Child and Adolescent Development (TCHAD) which includes all Swedish twins born in 1985-1986 (N = 2570). Internalizing and externalizing behavior problems were assessed with the Child Behavior Checklist at ages of 8-9, 13-14, 16-17, and 19-20 years. Individuals participating in TCHAD were followed regarding SA and DP during 2001-2013 using nationwide registers. Cox regression models were applied to assess hazard ratios (HR) with 95% confidence intervals (CI).

RESULTS

Each one-unit increase of rule-breaking behavior implied a significant higher risk for SA in early adulthood, despite of age at assessment, with the highest HR of 1.12 (95% CI 1.05-1.19) at age of 8-9 years. Higher levels of anxious and depressive symptoms in childhood and adolescence were associated with DP in early adulthood despite age at assessment, with the highest risk at age 19-20 years [HR 1.31 (95% CI 1.12-1.53)]. The associations attenuated slightly when familial factors were taken into account.

CONCLUSIONS

Internalizing and externalizing behavior problems identified at an early age (8-9 years) increased risk for SA and DP in young adulthood. These findings indicate that early prevention and intervention efforts to reduce behavior problems may promote a successful start in working life.

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

OBJECTIVE

To investigate whether psychosocial work environment and health behaviors are risk factors for sick leave due to mental disorders, and whether familial confounding (genetics and shared environment) explains the associations.

METHODS

Respondents (n = 11,729), given to complete a questionnaire in 2004 to 2006, were followed up approximately 5 years for sick leave spells due to mental disorders, using national registry data. Data were analyzed using logistic regression, and conditional logistic regression for twin pairs discordant for sick leave (cotwin control).

RESULTS

High job demands, job strain, and iso-strain were independent risk factors for sick leave due to mental disorders. Familial factors seem to be of importance in the associations between job support, smoking, a combination of unhealthy behaviors and sick leave.

CONCLUSIONS

Improving the psychosocial work environment may be effective in preventing sick leave due to mental disorders.

Stability and change of body mass index as a predictor of disability pension

AIMS

To investigate whether stability or change in body mass index (BMI) predict disability pension (DP) due to musculoskeletal diagnosis (MSD) when controlling for familial confounding.

METHODS

Our study cohort consisted of 17,169 Finnish twins born before 1958. Data on BMI and multiple covariates from questionnaires in 1975 and 1981 were included and DPs were collected from the national pension registers until the end of 2004. Cox proportional hazards regression models with Hazard Ratios (HR) and 95% Confidence Intervals (CI) were used for statistical analyses.

RESULTS

General DP was granted to 2853 individuals and DP due to MSD to 1143 individuals during the 23-year follow-up. A one-unit increase in BMI in both 1975 (HR 1.08, 95% CI 1.05, 1.10) and 1981 (HR 1.06, 95% CI 1.04, 1.07), as well as the stability of and change in BMI from 1975 to 1981 were all associated with an increased risk of DP. These associations held in the analyses controlling for multiple covariates (age, sex, socioeconomic status, education, marital status, leisure-time physical activity, and musculoskeletal pain), and mainly also familial confounding, that is, genetics and shared environment. HR for stable obesity was 2.28 (95% CI 1.69, 3.08) for DP due to MSD, and 1.91 (95% CI 1.56, 2.34) for general DP in the fully adjusted models. CONCLUSIONS BMI IS AN EARLY PREDICTOR OF GENERAL DP AND ALSO OF DP DUE TO MSD OWING TO THE INDEPENDENCY OF VARIOUS COVARIATES AND POTENTIALLY ALSO FAMILIAL CONFOUNDING, BMI MAY POSSIBLY HAVE A DIRECT EFFECT ON THE RISK OF DP.

Hyperthyroidism is associated with work disability and loss of labour market income. A Danish register-based study in singletons and disease-discordant twin pairs

OBJECTIVE

To examine the risk of disability pension and changes in labour market income in patients with hyperthyroidism.

METHODS

From a 5% random sample of the Danish population and twins from the Danish Twin Registry we identified 1942 hyperthyroid singletons and 7768 non-hyperthyroid (matched 1:4) controls as well as 584 same-sex twin pairs discordant for hyperthyroidism. Singletons and twins were followed for a mean of 9 years (range 1-20). Cox regression analysis was used to examine the risk of disability pension and a difference-in-differences model was used to evaluate changes in labour market income.

RESULTS

Hyperthyroid individuals had an increased risk of receiving disability pension: hazard ratio (HR) was 1.88, (95% CI: 1.57-2.24). Subdividing as to the cause of hyperthyroidism did not change this finding: Graves' disease (GD) HR was 1.51 (95% CI: 0.87-2.63) and toxic nodular goitre (TNG) HR was 2.10 (95% CI: 1.02-4.36). With respect to labour market income, the income of hyperthyroid individuals increased on average 1189 € less than their controls (P<0.001). This difference in income was more pronounced in GD (2539 €) than in TNG (132 €). Essentially similar results, with respect to disability pension and labour market income, were seen within monozygotic twin pairs discordant for hyperthyroidism.

CONCLUSION

Hyperthyroidism is associated with severe work disability as reflected by an 88% increased risk of receiving disability pension and a significant loss of labour market income. Similar results in monozygotic twins discordant for hyperthyroidism suggest that genetic confounding is unlikely.

The gender gap in sickness absence from work and the influence of parental absence on offspring absence 15 years later: register-based cohort of Norwegians born in 1974-1976

BACKGROUND

Women have shown consistently higher levels of sickness absence from work in comparison to men, but explanations for this gender gap have not been completely understood. Life-course studies suggest that health and health-related social benefits in adult age are influenced by early life experiences. We aimed to estimate intergenerational associations with a 15-year time gap between parents' and offspring sickness absences, pursuing the hypothesis that this parental influence would have a stronger impact for women than for men.

METHODS

All persons born alive between 1974 and 1976 in Norway were followed up in several national registries. Employed persons considered to be at risk of sickness absence and also with parents at risk of sickness absence (n = 78,878) were followed in the calendar year of their 33(rd) birthday with respect to spells lasting >16 days. The probability of one or more spells during this year constituted the one-year risk under study. Additive risk differences in association with an exposure (parental sickness absence 15 years earlier) were estimated in a binomial regression analysis. The estimates were adjusted for parental socioeconomic factors.

RESULTS

The 1-year sickness absence risk was higher for women (30.4%) than for men (12.3%). The crude risk differences between those exposed and those unexposed to parental sickness absence were similar in percentage points (PP) for women (3.8; 95% confidence interval (CI) 2.6 to 4.9) and men (3.8; 95% CI 2.9 to 4.6). The risk differences were moderately attenuated after adjustment for parental education and father's income to 3.4 PP (2.2 to 4.5) for women and 2.8 PP (2.0 to 3.7) for men. Male absence was more strongly associated with the father's than with the mother's sickness absence, while associations for women were stronger for the same diagnostic groups as their parents.

CONCLUSIONS

Parental sickness absence was moderately associated with sickness absence in the next generation. Bias from unmeasured confounders cannot be entirely dismissed. Contrary to our hypothesis, associations were not stronger for women than for men. If parental sickness absence has a long-term causal effect, preventive measures could have an impact over generations.

Socioeconomic status and sick leave granted for mental and somatic disorders: a prospective study of young adult twins

Background

Low socioeconomic status (SES), indicated by low income and education, has consistently been found to be a strong predictor of sick leave. Several possible pathways from SES to sick leave have been described in previous literature, but there are also evidence indicating that the association can be confounded by common underlying factors. This study utilizes a population-based sample of employed young adult twins to estimate (i) the degree to which education and income are prospectively related to sick leave granted for mental, somatic, and any disorder, and (ii) whether these associations are confounded by familial factors.

Methods

Registry data on educational attainment and income at age 30 and subsequent sick leave were available for 6,103 employed young adult twins, among which there were 2,024 complete twin pairs. The average follow-up time was 6.57 years. Individual-level associations and fixed effects within twin pairs were estimated.

Results

Low education and income were associated with sick leave granted for both mental and somatic disorders, and with sick leave granted for any disorder. Associations were attenuated within dizygotic twin pairs and reduced to non-significance within monozygotic twin pairs, suggesting influence of familial factors on the associations between SES and sick leave.

Conclusions

Low SES is associated with a higher level of sick leave granted for both mental and somatic disorders among young adults, but these associations are confounded by factors that are common to co-twins. Education and income are therefore not likely to strongly affect sick leave in young adulthood.

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

BACKGROUND

This study aims to assess whether the associations between burnout and sick leave due to stress-related mental disorders, other mental disorders, and somatic conditions are influenced by familial (genetic and shared environmental) factors.

METHODS

In this prospective cohort study, 23,611 Swedish twins born between 1959 and 1985, who answered a web-based questionnaire, including the Pines Burnout Measure 2004-2006, were included. Registry data on sick leave spells from the response date until December 31, 2010 were obtained from the Swedish Social Insurance Agency. Logistic regression analysis was performed to assess odds ratios with 95% confidence intervals for the association between burnout and sick leave for the whole sample, while conditional logistic regression of the same-sex discordant twin pairs was used to estimate the association between burnout and sick leave, adjusting for familial confounding. The Bivariate Cholesky models were used to assess whether the covariation between burnout and sick leave was explained by common genetic and/or shared environmental factors.

RESULTS

Burnout was a risk factor for sick leave due to stress-related and other mental disorders, and these associations were explained by familial factors. The phenotypic correlation between burnout and sick leave due to somatic conditions was 0.07 and the association was not influenced by familial factors. The phenotypic correlations between burnout and sick leave due to stress-related (0.26) and other mental disorders (0.30) were completely explained by common genetic factors.

CONCLUSIONS

The association between burnout and sick leave due to stress-related and other mental disorders seems to be a reflection of a shared genetic liability.

Associations between childbirth, hospitalization and disability pension: a cohort study of female twins

Background

As the literature on long-term effects of childbirth on risk of morbidity or permanent work incapacity (DP) is limited, we aimed to study associations of childbirth with hospitalization and DP, adjusting for familial factors.

Methods

This cohort study included female twins, i.e. women with twin sister, born 1959–1990 in Sweden (n = 5 118). At least one in the twin pair had their first childbirth 1994–2009. Women were followed regarding all-cause and cause-specific (mental or musculoskeletal diagnoses) DP during year 2–5 after first delivery or equivalent. Associations between childbirth, hospitalization and DP were calculated as hazard ratios (HR) with 95% confidence intervals (CI).

Results

Women who did not give birth had markedly higher number of DP days/year compared to those giving birth. Hospitalization after first childbirth was associated with a higher HR of DP. Those hospitalized at least once after their first childbirth had a three-fold DP risk (HR: 3.2; 95% CI 1.1–9.6), DP due to mental diagnoses (HR: 3.2; 1.2–8.8), and of DP due to musculoskeletal diagnoses (HR: 6.1; 1.6–22.9). Lower HRs in the discordant twin pair analyses indicated that familial factors may influence the studied associations.

Conclusions

Women who did not give birth had a much higher risk for DP than those who did. Among those who gave birth, the risk for DP was markedly higher among those with a previous hospitalization, and especially in women with repeated hospitalizations. The results indicate a health selection into giving birth as well as the importance of morbidity for DP.

Genetic and environmental contributions to the relationship between internalizing disorders and sick leave granted for mental and somatic disorders

This study investigates the degree to which internalizing disorders (anxiety and mood disorders) are prospectively associated with sick leave granted for mental and somatic disorders, and the extent to which common genetic and environmental risk factors influence these relationships. Data include self-reported symptoms of psychological distress from 7,598 young adult twins and diagnostic interviews on a subsample of 2,766 adult twins, subsequently linked to registry data on sick leave. Regression analyses and multivariate twin models were used to investigate the relationship between internalizing disorders and sick leave. Internalizing disorders were associated with sick leave granted for both mental disorders and somatic disorders. The association between internalizing disorders and sick leave granted for mental disorders was influenced by genetic and non-shared environmental factors, while the association between internalizing disorders and sick leave granted for somatic disorders could be explained by common genetic factors alone. Monozygotic twins discordant for internalizing disorders differed significantly in rates of sick leave granted for mental but not somatic disorders. In conclusion, internalizing disorders in young adults predict sick leave granted for both mental and somatic disorders. Environmental risk factors for internalizing disorders seem to influence sick leave granted for mental disorders, but not sick leave granted for somatic disorders.

Personality disorders and long-term sick leave: a population-based study of young adult Norwegian twins

Personality disorders (PDs) reduce global functioning, are associated with high levels of work disability, and are thus also likely to influence long-term sick leave (LTSL). Previous research has indicated significant genetic influence on both DSM-IV PDs and LTSL. To what degree genes contributing to PDs also influence LTSL has not been investigated. The aims of the current study were to investigate which PDs were significantly associated with LTSL, to what extent the genetic contributions to these PDs account for the heritability of LTSL, and to explore the hypothesis of a causal association between PDs and LTSL. The sample consisted of 2,771 young, adult Norwegian twins, born 1967-1979. PDs were assessed using the Structured Interview for DSM-IV Personality (SIDP-IV). The age range for the interview was 20-32. The data were subsequently linked to public records of LTSL (sick leave >16 days) up to 11 years later. The odds ratio for being in the highest LTSL category (>15% sick leave) when fulfilling the DSM-IV criteria for any PD diagnosis was 2.6 (1.8-3.8, 95% CI). Dimensional representations of schizotypal, paranoid, and borderline PD were independently and significantly associated with LTSL. The heritability of LTSL was 0.50. Genetic factors shared with the PDs accounted for 20% of this. The association between PDs and LTSL was due to shared genetic and not environmental influences, and was mainly explained by one common genetic factor. The hypothesis of a causal association was not supported, indicating that the association is explained by overlapping genetic liability between PDs and LTSL.