Publications by authors named "Jurgita Narusyte"

39 Publications

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

BMC Health Serv Res 2021 Apr 7;21(1):315. Epub 2021 Apr 7.

Department of Clinical Neuroscience, Division of Insurance Medicine, Karolinska Institutet, SE-171 77, Stockholm, Sweden.

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.
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http://dx.doi.org/10.1186/s12913-021-06310-wDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8028110PMC
April 2021

Sleep duration and mortality - Influence of age and occupational group in retired individuals.

Sleep Med 2021 Apr 3;80:199-203. Epub 2021 Feb 3.

Division of Insurance Medicine, Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden.

The importance of sleep duration for health or mortality attracts much public attention. Prior work indicates that both long and short sleep duration predicts mortality, with optimal sleep duration (lowest risk) at 7 h. However, we believe this may differ between subgroups. This may be the case with, for example, age groups (due to aging), or blue-collar and white-collar worker (due to work exposure). It is also likely that retirement, which permits extension of the time in bed, may confound analyses. The purpose of the present study was to investigate how occupational group (blue-collar/white-collar worker) and age influence the pattern of association between sleep duration and mortality in retired individuals. Retired individuals were selected since it was hypothesized that effects of occupation may accumulate over years and since the transition into retirement may be a confounder. We used a sample of 14 000 individuals from the Swedish Twin Registry, which had provided data on sleep duration and a number of covariates. Cox proportional hazards analysis was applied to data. The results show that occupational group did not influence the association, but showed significant hazard ratios (HR) for long (≥9.5 h) and short (<6.5 h) sleep in both groups (HR > 1.35), with optimal sleep duration (lowest HR) with a wide span (6.5-9.5 h). Age groups in tertiles also showed significant U-shapes, with a wide span (6.5-9.5 h) for the younger 2/3 (54-74 years), but a weaker pattern for the oldest third (≥75 years), for which optimal sleep fell in the 6.5-7.5 h interval. It was concluded that occupational group does not influence the association between sleep duration and mortality in retired individuals, but that age does.
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http://dx.doi.org/10.1016/j.sleep.2021.01.058DOI Listing
April 2021

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

BMC Public Health 2020 Oct 6;20(1):1507. Epub 2020 Oct 6.

Division of Insurance Medicine, Department of Clinical Neuroscience, Karolinska Institutet, SE-171 77, Stockholm, Sweden.

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.
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http://dx.doi.org/10.1186/s12889-020-09567-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7541297PMC
October 2020

Adverse outcomes of chronic widespread pain and common mental disorders in individuals with sickness absence - a prospective study of Swedish twins.

BMC Public Health 2020 Aug 27;20(1):1301. Epub 2020 Aug 27.

Division of Insurance Medicine, Department of Clinical Neuroscience, Karolinska Institutet, SE-171 77, Stockholm, Sweden.

Background: Chronic widespread pain (CWP) and common mental disorders (CMDs) are common public health problems, but little is known about the role of CWP and CMDs on future adverse outcomes among work disabled individuals. The aims of the study were to investigate the associations between CWP and CMDs with subsequent disability pension (DP), long-term unemployment (> 90 days) and all-cause mortality in individuals with sickness absence (SA) and whether the associations were explained by familial factors.

Methods: In this prospective cohort study, 7884 Swedish twins born between 1933 and 1985 were included and baseline data were gathered from a questionnaire in 1998 to 2006. Register data were used for obtaining information regarding demographics, SA, DP, unemployment and mortality. Cox proportional hazards regressions were used to calculate Hazard Ratios (HR) with 95% Confidence Intervals (CI) for the associations between CWP and/or CMDs with DP, unemployment and mortality, while conditional Cox models for twin pairs provided control for familial confounding.

Results: Having either CWP or CMDs among those with a history of SA was associated with a higher risk of DP and all-cause mortality than individuals without CWP and CMDs after controlling for socio-demographic and health factors. Moreover, sick-listed individuals with both CWP and CMDs had a higher risk of DP while those who only had CMDs had a higher risk of long-term unemployment compared to those without CWP and CMDs. The association between CMDs with DP and long-term unemployment was no longer significant when controlling for familial factors.

Conclusions: CMDs was a risk factor for DP, unemployment and mortality among individuals with SA, while CWP seems to be important in relation to future DP and mortality. Familial factors played a role in the associations between CMDs and DP and CMDs and unemployment.
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http://dx.doi.org/10.1186/s12889-020-09407-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7457303PMC
August 2020

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

Eur J Pain 2020 11 17;24(10):1892-1901. Epub 2020 Aug 17.

Division of Insurance Medicine, Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden.

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.
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http://dx.doi.org/10.1002/ejp.1635DOI Listing
November 2020

Night work, mortality, and the link to occupational group and sex.

Scand J Work Environ Health 2020 09 9;46(5):508-515. Epub 2020 Apr 9.

Department of Clinical Neuroscience, Karolinska Institutet, 17177 Stockholm, Sweden.

Objective Night shifts are associated with several major diseases. Mortality has been studied only to a limited extent, and the association with night shifts remains unclear. The purpose of the present study was to investigate the association between duration of night shift exposure and mortality in a large sample from the Swedish Twin Registry (the SALT cohort). Methods Cox proportional hazards regression models were used to analyze the data (N=42 731) over a follow-up period of 18 years, with years of night shift work as the exposure variable and adjustment for lifestyle factors and age, and stratification on gender and occupational group. Results The hazard ratio (HR) for "ever" night shifts for total mortality was 1.07 [95% confidence interval (CI) 1.01-1.15] but 1.15 (95% CI 1.07-1.25) for longer exposure (>5 years). Also, HR for cause-specific mortality due to cardiovascular disease was significant, with higher HR for longer night shift exposure. Mortality due to cancer was significant for longer exposure only. White-collar workers showed significant HR for longer exposure. In particular, male white-collar workers showed a significant HR, with a highest value for longer exposure [HR 1.28 (95% CI 1.09-1.49)]. Heredity did not influence the results significantly. Conclusions Long duration of exposure to night shift work is associated with increased mortality, particularly in male white-collar workers. The lack of effects of accumulated exposure suggests that the results should be interpreted with caution.
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http://dx.doi.org/10.5271/sjweh.3892DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7737802PMC
September 2020

Shared liability to pain, common mental disorders, and long-term work disability differs among women and men.

Pain 2020 05;161(5):1005-1011

Division of Insurance Medicine, Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden.

Knowledge of factors involved in the associations between pain, common mental disorders, and future work incapacity is still scarce. The aim of this study was to examine the overlap between genetic and environmental factors contributing to depression/anxiety, pain, and future long-term sickness absence (SA) and disability pension (DP) among women and men. The study sample included 47,995 twins born in Sweden 1935 to 1985. Information on self-reported depression/anxiety and back, neck, and shoulder pain was obtained from surveys conducted 1998 to 2002 and 2004 to 2005. Data on long-term SA (>365 days) and DP due to mental and/or musculoskeletal disorders until 2013 were obtained from the National Social Insurance Agency. Shared genetic and environmental influences on depression/anxiety, pain, and SA/DP were estimated by applying structural equation modeling. The prevalence of depression/anxiety was 27% and 14% among women and men, for pain 24% and 19%, and for SA/DP due to mental and musculoskeletal diagnoses 7% and 4%, respectively. Multivariate biometric analyses revealed different patterns of covariation between the 3 phenotypes among women and men. For women, a latent-shared liability to all 3 phenotypes could be identified, mainly attributable to genetic factors (66%). For men, no shared underlying liability was observed. The variation in SA/DP was explained by genetic factors in common with depression/anxiety by 27% and in common with pain by 9%. Common mental disorders, pain, and SA/DP tend to covariate in different ways among women and men. The results may have clinical implications as strategies preventing SA/DP may be different among women and men.
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http://dx.doi.org/10.1097/j.pain.0000000000001787DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7170444PMC
May 2020

The refugee post-migration stress scale (RPMS) - development and validation among refugees from Syria recently resettled in Sweden.

Confl Health 2020 6;14. Epub 2020 Jan 6.

1Department of Health Sciences, The Swedish Red Cross University College, PO Box 1059, 141 21 Huddinge, Sweden.

Background: Despite the growing recognition of the impact of post-resettlement factors on the mental health of refugees, a clear definition of the concept of post-migration stress, as well as an updated, valid instrument for assessing the construct, are still lacking. The aim of the current study was to develop and validate the Refugee Post-Migration Stress Scale (RPMS), a concise, multi-dimensional instrument for assessing post-migration stress among refugees.

Results: Based on a review of previous research and observations from a refugee trauma clinic, a preliminary 24-item instrument was developed, covering seven hypothesized domains of post-migration stress: and .In the context of a population-based survey of mental health among refugees from Syria recently resettled in Sweden ( = 1215), the factorial structure of the RPMS was investigated. Confirmatory Factor Analysis revealed slightly insufficient fit for the initial theorized multi-domain model. Exploratory Factor Analysis in four iterations resulted in the omission of three items and an adequate fit of a 7-factor model, corresponding to the seven hypothesized domains of post-migration stress. To assess concurrent validity, correlational analyses with measures of anxiety, depression, post-traumatic stress disorder (PTSD), and mental wellbeing were carried out. All domains of post-migration stress showed significant correlations with anxiety, depression, and PTSD scores, and significant negative correlations with mental wellbeing scores.

Conclusions: The newly developed RPMS appears to be a valid instrument for assessing refugee post-migration stress. Our findings that post-migration stress primarily relating to social and economic factors seems to be associated with mental ill health among refugees is in line with previous research.
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http://dx.doi.org/10.1186/s13031-019-0246-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6945710PMC
January 2020

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

BMC Musculoskelet Disord 2019 Dec 26;20(1):622. Epub 2019 Dec 26.

Division of Insurance Medicine, Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden.

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.
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http://dx.doi.org/10.1186/s12891-019-2999-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6933729PMC
December 2019

Transitioning from sickness absence to disability pension-the impact of poor health behaviours: a prospective Swedish twin cohort study.

BMJ Open 2019 11 10;9(11):e031889. Epub 2019 Nov 10.

Division of Insurance Medicine, Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden

Objectives: To investigate the association between three poor health behaviours (current smoker, high consumption of alcohol and low physical activity levels) and the transition to disability pension (DP) among individuals who have recently been sickness absent. Furthermore, we aimed to explore whether having multiple poor health behaviours increased the risk of transitioning from sickness absence (SA) to DP.

Design: Prospective twin cohort study.

Setting: Sweden.

Participants: Twins aged 20-46 who had participated in a survey and been on SA (>14 days) in the year preceding baseline (date of answering the questionnaire).

Main Outcome Measure: Incident DP during the follow-up which ended on 31 December 2012 (mean 5.2 years). A national register with full coverage provided data on DP.

Results: The Cox proportional-hazards regression analyses showed that current smokers had a higher risk of transitioning from SA to DP compared with never smokers (HR 1.76; 95% CI 1.08 to 2.84). Alcohol use and lack of physical activity as well as poor health behaviour sum score showed no significant associations.

Conclusions: Being a current smoker influences the transition from SA to DP. Although non-significant, there were indications that more physical activity and fewer poor health behaviours could reduce the risk of exiting the labour market through DP. Improving health behaviours among people on SA could be a valuable tool for preventing the transition to DP.
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http://dx.doi.org/10.1136/bmjopen-2019-031889DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6858211PMC
November 2019

Number of Pain Locations as a Predictor of Cause-Specific Disability Pension in Sweden-Do Common Mental Disorders Play a Role?

J Occup Environ Med 2019 08;61(8):646-652

Finnish Institute of Occupational Health, Työterveyslaitos, Finland (Dr Ropponen), Division of Insurance Medicine, Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden (Drs Ropponen, Narusyte, Mittendorfer-Rutz, Svedberg).

Objective: The aim of this study was to investigate the associations between number of pain locations, common mental disorders (CMDs), and disability pension (DP).

Methods: Survey data in 1998 to 2003 for 27,165 Swedish twins born in 1935 to 1958 were linked to national DP data until 2013. Pain locations were evaluated for back, low back, sciatica, shoulder, or neck pain, and CMDs for lifetime major depression and 1-month anxiety.

Results: The number of pain locations was associated with DP in a dose-response manner. One pain location had a hazard ratio of 1.50 (95% confidence interval 1.35 to 1.68) and five pain locations hazard ratio 4.67 (95% confidence interval 4.11 to 5.30) for DP. Also, CMDs were associated with DP.

Conclusion: The number of pain locations has a dose-response association with the risk of DP. CMDs predict DP. In strategies to prevent DP, early signs of pain or CMDs should be taken into consideration.
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http://dx.doi.org/10.1097/JOM.0000000000001635DOI Listing
August 2019

The role of occupational class on the association between sickness absence and disability pension: A Swedish register-based twin study.

Scand J Work Environ Health 2019 11 20;45(6):622-630. Epub 2019 Mar 20.

Division of Insurance Medicine, Department of Clinical Neuroscience, Karolinska Institutet, Berzeliusväg 3, 171 77 Stockholm, Sweden.

Objectives The aim of this study was to examine the association between long-term sickness absence (LTSA) due to mental disorders and musculoskeletal disorders and all-cause disability pension (DP) among blue- and white-collar workers. A secondary objective was to examine the influence of familial factors on the associations. Methods This was a prospective twin cohort study of 42 984 individuals (21-64 years at baseline), 3017 of whom had a new LTSA spell (>14 days) due to mental or musculoskeletal disorders in 2005-2006. Average follow-up time was 5.4 years. Survey data on occupational class and register data on LTSA and DP were used. Cox proportional hazards regression was applied to calculate hazards ratios (HR) with 95% confidence intervals (CI). Results During follow-up, 989 participants went on disability. LTSA due to mental disorders and musculoskeletal disorders led to similar HR for DP among both white- and blue-collar workers when compared to white-collar workers not on LTSA (reference group). LTSA ≥6 months due to musculoskeletal disorders was associated with a higher risk of DP for white-collar (HR 31.50, 95% CI 20.45-48.52) than blue-collar (HR 17.64, 95% CI 13.08-23.78) workers when compared to the reference group. HR were lower in the discordant twin pair models for LTSA due to mental disorders than in the whole cohort. Conclusions White-collar workers on LTSA due to musculoskeletal disorders are especially vulnerable to all-cause DP. This pattern was not present for LTSA due to mental disorders. Familial factors seem to influence the association between LTSA due to mental disorders and all-cause DP.
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http://dx.doi.org/10.5271/sjweh.3816DOI Listing
November 2019

Associations between adolescent social phobia, sickness absence and unemployment: a prospective study of twins in Sweden.

Eur J Public Health 2019 10;29(5):931-936

Division of Insurance Medicine, Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden.

Background: Little is known about adolescent mental health problems, including social phobia, as risk factors for future work incapacity. The aim of this study was to investigate the association between social phobia in adolescence and unemployment and sickness absence (SA) in early adulthood, also evaluating the role of familial factors (genetics and shared environment).

Methods: A sample of 2845 Swedish twins born in 1985-86 in Sweden was followed longitudinally in the population-based and prospective Twin study of CHild and Adolescent Development. Information on twins' social phobia was collected at ages 13-4, 16-7 and 19-20 years. Logistic regression providing odds ratios (OR) with 95% confidence intervals (95% CI) was used to analyze the associations between social phobia, unemployment and SA during the follow-up 2006-12. The influence of familial factors was evaluated by conditional logistic regression.

Results: Presence of social phobia during adolescence was associated with increased odds for unemployment and SA in young adulthood. For unemployment, the highest OR was at the age of 13-4 years (1.58 [95% CI: 1.22-2.06]), and the associations became null after adjusting for familial factors. For SA, the highest OR was at the age of 19-20 years (1.73 [95% CI: 1.13-2.65]), and the estimates changed slightly after adjusting for familial factors.

Conclusions: : Results suggest that social phobia experienced in adolescence contribute to early adulthood unemployment and SA. Familial factors seemed to explain the association between social phobia and unemployment.
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http://dx.doi.org/10.1093/eurpub/ckz033DOI Listing
October 2019

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

Chronobiol Int 2018 02 16;35(2):249-260. Epub 2017 Nov 16.

b Division of Insurance Medicine, Department of Clinical Neuroscience , Karolinska Institutet , Stockholm , 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.
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http://dx.doi.org/10.1080/07420528.2017.1399137DOI Listing
February 2018

Sleep Duration, Mortality, and Heredity-A Prospective Twin Study.

Sleep 2017 10;40(10)

Division of Insurance Medicine, Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden.

Introduction: A number of studies have shown a U-shaped association between sleep duration and mortality. Since sleep duration is partly genetically determined, it seems likely that its association with mortality is also genetically influenced. The purpose of the present study was to investigate the influence on heredity on the association between sleep duration and mortality.

Methods: We used a cohort of 14267 twins from the Swedish Twin Registry.

Results: A Cox proportional hazards regression analysis, adjusted for a number of covariates, confirmed a clear U shape with a hazard ratio (HR) = 1.34 and 95% confidence interval (CI) = 1.15-1.57 for a sleep duration of ≤6.5 hours and HR = 1.18 (CI = 1.07-1.30) for sleep of ≥9.5 hours. Reference value was 7.0 hours. A co-twin analysis of 1942 twins discordant on mortality showed a HR = 2.66 (CI = 1.17-6.04) for long (≥9.5 hours) sleep in monzygotic twins and an HR = 0.66 (CI = 0.20-2.14) for short (<6.5 hours) sleep. In dizygotic twins, no association was significant. The heritability for mortality was 28% for the whole group, while it was 86% for short sleepers and 42% for long sleepers. Thus, the link with mortality for long sleep appears to be more due to environmental factors than to heredity, while heritability dominates among short sleepers.

Conclusions: We found that both long and short sleep were associated with higher total mortality, that the difference in mortality within twin pairs is associated with long sleep, and that short sleep has a higher heritability for mortality, while long sleep is associated with more environmental influences on mortality.
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http://dx.doi.org/10.1093/sleep/zsx135DOI Listing
October 2017

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

Soc Psychiatry Psychiatr Epidemiol 2017 09 21;52(9):1159-1168. Epub 2017 Jun 21.

Division of Insurance Medicine, Department of Clinical Neuroscience, Karolinska Institute, 17177, Stockholm, Sweden.

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.
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http://dx.doi.org/10.1007/s00127-017-1409-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5581816PMC
September 2017

Night work as a risk factor of future disability pension due to musculoskeletal diagnoses: a prospective cohort study of Swedish twins.

Eur J Public Health 2017 08;27(4):659-664

Division of Insurance Medicine, Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden.

Background: This study investigated the associations between night work, sleep and disability pension (DP) due to musculoskeletal disorders (MSD), while controlling for several confounding factors including both genetic factors and shared family background.

Methods: The study sample consisted of 27 165 Swedish twin individuals born in 1935-58 with comprehensive survey data on sociodemographic, health and lifestyle factors. Night work was assessed as years of working hours at night at least every now and then, and categorized into 'not at all, 1-10 years and over 10 years'. Data on DP with MSD (ICD-diagnoses M00-M99) were obtained from the National Social Insurance Agency. Follow-up was from the time of the interview in 1998-2003 until 2013. Information on the length and quality of sleep was available for a sub-sample of twins (n = 1684). Cox proportional hazards models were used to calculate hazard ratios (HR) with 95% confidence intervals (CI).

Results: During the follow-up, 1338 (5%) participants were granted DP due to MSD. Both 1-10 years (HR 1.33, 95% CI 1.17-1.53) and over 10 years of night work (HR 1.39 95% CI 1.18-1.64) increased the risk of future DP. The associations were not affected by health, lifestyle or sleep factors. In the discordant twin pair analysis, the associations between night work and DP due to MSD attenuated.

Conclusions: Night work was associated with increased risk of DP due to MSD independently from health and lifestyle factors. Familial confounding could not be ruled out.
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http://dx.doi.org/10.1093/eurpub/ckx084DOI Listing
August 2017

Night work and prostate cancer in men: a Swedish prospective cohort study.

BMJ Open 2017 06 8;7(6):e015751. Epub 2017 Jun 8.

Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden.

Objectives: Prostate cancer is the most common cancer and the second leading cause of cancer-related deaths among men, but the contributing factors are unclear. One such may be night work because of the day/night alternation of work and the resulting disturbance of the circadian system. The purpose of the present study was to investigate the prospective relation between number of years with night work and prostate cancer in men.

Design: Cohort study comparing night and day working twins with respect to incident prostate cancer in 12 322 men.

Setting: Individuals in the Swedish Twin Registry.

Participants: 12 322 male twins.

Outcome Measures: Prostate cancer diagnoses obtained from the Swedish Cancer Registry with a follow-up time of 12 years, with a total number of cases=454.

Results: Multiple Cox proportional hazard regression analysis, adjusted for a number of covariates, showed no association between ever night work and prostate cancer, nor for duration of night work and prostate cancer. Analysis of twin pairs discordant for prostate cancer (n=332) showed no significant association between night work and prostate cancer.

Conclusions: The results, together with previous studies, suggest that night work does not seem to constitute a risk factor for prostate cancer.
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http://dx.doi.org/10.1136/bmjopen-2016-015751DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5541514PMC
June 2017

Genetic and environmental influences on the association between performance-based self-esteem and exhaustion: A study of the self-worth notion of burnout.

Scand J Psychol 2016 Oct 25;57(5):419-26. Epub 2016 Jul 25.

Division of Insurance Medicine, Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden.

In the self-worth model, burnout is considered to be a syndrome of performance-based self-esteem (PBSE) and experiences of exhaustion. Studies have shown that PBSE and burnout indices such as Pines' Burnout Measure (BM) are associated. Whether these variables have overlapping etiologies has however not been studied before. Genetic and environmental components of covariation between PBSE and exhaustion measured with Pines' BM were examined in a bivariate Cholesky model using data from 14,875 monozygotic and dizygotic Swedish twins. Fifty-two per cent of the phenotypic correlation (r = 0.41) between PBSE and Pines' BM was explained by genetics and 48% by environmental factors. The findings of the present study strengthen the assumption that PBSE should be considered in the burnout process as proposed by the self-worth conception of burnout. The present results extend our understanding of the link between this contingent self-esteem construct and exhaustion and provide additional information about the underlying mechanisms in terms of genetics and environment. This finding corroborates the assumed syndrome view on burnout, while it also suggests an altered view of how the syndrome emerges and how it can be alleviated.
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http://dx.doi.org/10.1111/sjop.12309DOI Listing
October 2016

Associations between the parent-child relationship and adolescent self-worth: a genetically informed study of twin parents and their adolescent children.

J Child Psychol Psychiatry 2017 01 18;58(1):46-54. Epub 2016 Jul 18.

Institute of Psychiatry, Psychology & Neuroscience, MRC Social, Genetic & Developmental Psychiatry Centre, King's College London, London, UK.

Background: Low self-worth during adolescence predicts a range of emotional and behavioural problems. As such, identifying potential sources of influence on self-worth is important. Aspects of the parent-child relationship are often associated with adolescent self-worth but to date it is unclear whether such associations may be attributable to familial confounding (e.g. genetic relatedness). We set out to clarify the nature of relationships between parental expressed affection and adolescent self-worth, and parent-child closeness and adolescent self-worth.

Methods: We used data from the Twin and Offspring Study in Sweden, a children-of-twins sample comprising 909 adult twin pairs with adolescent children. Using these data we were able to apply structural equation models with which we could examine whether associations remained after accounting for genetic transmission.

Results: Results demonstrated that parent-child closeness and parental-expressed affection were both phenotypically associated with adolescent self-worth. Associations could not be attributed to genetic relatedness between parent and child.

Conclusions: Parent-child closeness and parental affection are associated with adolescent self-worth above and beyond effects attributable to genetic relatedness. Data were cross-sectional, so the direction of effects cannot be confirmed but findings support the notion that positive parent-child relationships increase adolescent self-worth.
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http://dx.doi.org/10.1111/jcpp.12600DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5215430PMC
January 2017

Physical and verbal aggressive behavior and COMT genotype: Sensitivity to the environment.

Am J Med Genet B Neuropsychiatr Genet 2016 07 17;171(5):708-18. Epub 2016 Feb 17.

Center for Clinical Research, Uppsala University, County Hospital, Västerås, Sweden.

Catechol-O-methyltransferase (COMT) genotype has been implicated as a vulnerability factor for several psychiatric diseases as well as aggressive behavior, either directly, or in interaction with an adverse environment. The present study aimed at investigating the susceptibility properties of COMT genotype to adverse and favorable environment in relation to physical and verbal aggressive behavior. The COMT Val158Met polymorphism was genotyped in a Swedish population-based cohort including 1,783 individuals, ages 20-24 years (47% males). A significant three-way interaction was found, after correction for multiple testing, between COMT genotype, exposure to violence, and parent-child relationship in association with physical but not verbal aggressive behavior. Homozygous for the Val allele reported lower levels of physical aggressive behavior when they were exposed to violence and at the same time experienced a positive parent-child relationship compared to Met carriers. Thus, susceptibility properties of COMT genotype were observed in relation to physical aggressive behavior supporting the hypothesis that COMT genotypes are modifying the sensitivity to environment that confers either risk or protection for aggressive behavior. As these are novel findings, they warrant further investigation and replication in independent samples. © 2016 Wiley Periodicals, Inc.
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http://dx.doi.org/10.1002/ajmg.b.32430DOI Listing
July 2016

Genetic and Environmental Influences on Disability Pension Due To Mental Diagnoses: Limited Importance of Major Depression, Generalized Anxiety, and Chronic Fatigue.

Twin Res Hum Genet 2016 Feb 9;19(1):10-6. Epub 2015 Dec 9.

Division of Insurance Medicine,Department of Clinical Neuroscience,Karolinska Institutet,Stockholm,Sweden.

Background: Previous research indicates that liability to disability pension (DP) due to mental diagnoses is moderately influenced by genetic factors. This study investigates whether genetic contributions to the liability to DP due to mood and neurotic diagnoses overlap with the genetic influences on major depression (MD), generalized anxiety disorder (GAD), or chronic fatigue (CF).

Method: A prospective cohort study including 9,985 female twins born in Sweden 1933-1958. The presence of MD, GAD, and CF was assessed by computer-assisted telephone interviews conducted in 1998-2002. Data on DP due to mood and neurotic diagnoses were obtained from nationwide registers for the years 1998-2010. Common genetic and environmental influences on the phenotypes were estimated by applying structural equation modeling.

Results: The prevalence of MD/GAD was 30%, CF 8%, and DP due to mood and neurotic diagnoses 3% in 2010. Genetic effects on MD/GAD explained 31% of the total genetic variation in DP, whereas genetic contributions in common with CF were small and not significant. The majority of the total non-shared environmental variance in DP (85%) was explained by the factors that were unique to DP.

Conclusions: Large proportions of genetic and non-shared environmental influences in DP due to mood and neurotic diagnoses were not explained by the contributions from MD/GAD or CF. The results suggest that the process leading to DP is complex and influenced by factors other than those related to the disorder underlying DP.
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http://dx.doi.org/10.1017/thg.2015.86DOI Listing
February 2016

Occurrence of sickness absence and disability pension in relation to childbirth: A 16-year follow-up study of 6323 Swedish twins.

Scand J Public Health 2016 Feb 12;44(1):98-105. Epub 2015 Oct 12.

Department of Clinical Neuroscience, Division of Insurance Medicine, Karolinska Institutet, Sweden.

Background: Pregnancy, delivery, and the postpartum period may imply morbidity leading to work incapacity; however, this is seldom studied. This study aimed to compare twin sisters giving or not giving birth regarding occurrence of sickness absence (SA) and disability pension (DP).

Methods: This population-based cohort study included all 6323 female twins born in Sweden 1959-1990, using register data for 1994-2010 about SA and DP. Average number of SA/DP days/year was calculated in relation to the year of the first delivery, or, if not giving birth, the year when the twin sister gave birth. Twin pairs discordant for delivery were used to investigate the importance of genetic and environmental factors for occurrence of SA and DP.

Results: In all, 52% had a first delivery during 1994-2010. Except for the year of delivery, the average number of SA days/year was similar when comparing women who gave birth to those who did not, while number of DP days was significantly higher in women who did not give birth. Differences between the groups seem attributable to genetic factors. Women who delivered once had higher levels of SA and DP than those who had several deliveries. DP with mental diagnoses was more common among women who had not delivered whereas DP with musculoskeletal diagnoses occurred more often among women who delivered.

Conclusions: Levels of SA were similar among women who gave birth and who did not. Women not giving birth had significantly higher levels of DP, indicating health selections into childbirth.
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http://dx.doi.org/10.1177/1403494815610051DOI Listing
February 2016

The Intergenerational Transmission of Anxiety: A Children-of-Twins Study.

Am J Psychiatry 2015 Jul 23;172(7):630-7. Epub 2015 Apr 23.

From King's College London, MRC Social, Genetic and Developmental Psychiatry Research Centre, the Institute of Psychiatry, Psychology and Neuroscience, London; the Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden; the Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden; Yale Child Study Center, New Haven, Conn.; the Office of Behavioral and Social Sciences Research, NIH, Bethesda, Md.; the Department of Psychology, George Washington University, Washington, DC; and the Department of Psychology, The Pennsylvania State University, University Park, Pa.

Objective: The transmission of anxiety within families is well recognized, but the underlying processes are poorly understood. Twin studies of adolescent anxiety demonstrate both genetic and environmental influence, and multiple aspects of parenting are associated with offspring anxiety. To date, the children-of-twins design has not been used to evaluate the relative contributions of genetic transmission compared with direct transmission of anxiety from parents to their offspring.

Method: Anxiety and neuroticism measures were completed by 385 monozygotic and 486 dizygotic same-sex twin families (37% male twin pair families) from the Twin and Offspring Study in Sweden. Structural equation models tested for the presence of both genetic and environmental transmission from one generation to the next.

Results: For both anxiety and neuroticism, the models provide support for significant direct environmental transmission from parents to their adolescent offspring. In contrast, there was no evidence of significant genetic transmission.

Conclusions: The association between parental and offspring anxiety largely arises because of a direct association between parents and their children independent of genetic confounds. The lack of genetic transmission may reflect there being different genetic effects on these traits in adolescence and adulthood. Direct environmental transmission is in line with developmental theories of anxiety suggesting that children and adolescents learn anxious behaviors from their parents through a number of pathways such as modeling. Future analyses should combine children-of-twins data with child twin data in order to examine whether this direct effect solely represents parental influences on the offspring or whether it also includes child/adolescent anxiety evoking parental anxiety.
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http://dx.doi.org/10.1176/appi.ajp.2015.14070818DOI Listing
July 2015

Night work and breast cancer in women: a Swedish cohort study.

BMJ Open 2015 Apr 15;5(4):e008127. Epub 2015 Apr 15.

Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden.

Objectives: Recent research has suggested a moderate link between night work and breast cancer in women, mainly through case-control studies, but non-significant studies are also common and cohort studies are few. The purpose of the present study was to provide new information from cohort data through investigating the association between the number of years with night work and breast cancer among women.

Design: Cohort study of individuals exposed to night shift work in relation to incidence of breast cancer in women.

Setting: Individuals in the Swedish Twin registry, with follow-up in the Swedish Cancer Registry.

Participants: 13,656 women from the Swedish Twin Registry, with 3404 exposed to night work.

Outcome Measures: Breast cancer from the Swedish Cancer Registry (463 cases) during a follow-up time of 12 years.

Results: A Cox proportional hazards regression analysis with control for a large number of confounders showed that the HR was HR=1.68 (95% CI 0.98 to 2.88) for the group with >20 years of night work. When the follow-up time was limited to ages below 60 years, those exposed >20 years showed a HR=1.77 (95% CI 1.03 to 3.04). Shorter exposure to night work showed no significant effects.

Conclusions: The present results, together with previous work, suggest that night work is associated with an increased risk of breast cancer in women, but only after relatively long-term exposure.
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http://dx.doi.org/10.1136/bmjopen-2015-008127DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4401866PMC
April 2015

Parental criticism is an environmental influence on adolescent somatic symptoms.

J Fam Psychol 2015 Apr;29(2):283-9

Department of Psychology, Pennsylvania State University.

Previous studies have suggested that parental criticism leads to more somatic symptoms in adolescent children. However, this research has not assessed the direction of causation or whether genetic and/or environmental influences explain the association between parental criticism and adolescent somatic symptoms. As such, it is impossible to understand the mechanisms that underlie this association. The current study uses the Extended Children of Twins design to examine whether parents' genes, adolescents' genes, and/or environmental factors explain the relationship between parental criticism and adolescent somatic symptoms. Participants came from 2 twin samples, including the Twin and Offspring Study in Sweden (N = 868 pairs of adult twins and each twin's adolescent child) and from the Twin Study of Child and Adolescent Development (N = 690 pairs of twin children and their parents). Findings showed that environmental influences account for the association between parental criticism and adolescent somatic symptoms. This suggests that parents' critical behaviors exert a direct environmental effect on somatic symptoms in adolescent children. Results support the use of intervention programs focused on parental criticism to help reduce adolescents' somatic symptoms.
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http://dx.doi.org/10.1037/fam0000065DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4432933PMC
April 2015

Childbirth, hospitalisation and sickness absence: a study of female twins.

BMJ Open 2015 Jan 8;5(1):e006033. Epub 2015 Jan 8.

Division of Insurance Medicine, Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden.

Objective: To investigate associations of giving birth with morbidity in terms of hospitalisation and social consequences of morbidity in terms of sickness absence (SA), while taking familial (genetics and shared environmental) factors into account.

Design: Prospective register-based cohort study. Estimates of risk of hospitalisation and SA were calculated as HRs with 95% CIs.

Setting: All female twins, that is, women with a twin sister, born in Sweden.

Participants: 5118 Swedish female twins (women with a twin sister), born during 1959-1990, where at least one in the twin pair had their first childbirth (T0) during 1994-2009 and none gave birth before 1994.

Main Outcome Measures: Hospitalisation and SA during year 3-5 after first delivery or equivalent.

Results: Preceding the first childbirth, the mean annual number of SA days increased for mothers, and then decreased again. Hospitalisation after T0 was associated with higher HRs of short-term and long-term SA (HR for short-term SA 3.0; 95% CI 2.5 to 3.6 and for long-term SA 2.3; 95% CI 1.6 to 3.2). Hospitalisation both before and after first childbirth was associated with a higher risk of future SA (HR for long-term SA 4.2; 95% CI 2.7 to 6.4). Familial factors influenced the association between hospitalisation and long-term SA, regardless of childbirth status.

Conclusions: Women giving birth did not have a higher risk for SA than those not giving birth and results indicate a positive health selection into giving birth. Mothers hospitalised before and/or after giving birth had higher risks for future SA, that is, there was a strong association between morbidity and future SA.
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http://dx.doi.org/10.1136/bmjopen-2014-006033DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4289737PMC
January 2015

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

PLoS One 2014 7;9(7):e101566. Epub 2014 Jul 7.

Department of Clinical Neuroscience, Division of Insurance Medicine, Karolinska Institutet, Stockholm, Sweden.

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.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0101566PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4084814PMC
February 2015

Parental knowledge is an environmental influence on adolescent externalizing.

J Child Psychol Psychiatry 2015 Feb 30;56(2):130-7. Epub 2014 Jun 30.

Center for Alcohol and Addiction Studies, Brown University, Providence, RI, USA; Division of Behavior Genetics, Department of Psychiatry, Rhode Island Hospital.

Background: There is evidence both that parental monitoring is an environmental influence serving to diminish adolescent externalizing problems and that this association may be driven by adolescents' characteristics via genetic and/or environmental mechanisms, such that adolescents with fewer problems tell their parents more, and therefore appear to be better monitored. Without information on how parents' and children's genes and environments influence correlated parent and child behaviors, it is impossible to clarify the mechanisms underlying this association.

Method: The present study used the Extended Children of Twins model to distinguish types of gene-environment correlation and direct environmental effects underlying associations between parental knowledge and adolescent (age 11-22 years) externalizing behavior with a Swedish sample of 909 twin parents and their adolescent offspring and a US-based sample of 405 White adolescent siblings and their parents.

Results: Results suggest that more parental knowledge is associated with less adolescent externalizing via a direct environmental influence independent of any genetic influences. There was no evidence of a child-driven explanation of the association between parental knowledge and adolescent externalizing problems.

Conclusions: In this sample of adolescents, parental knowledge exerted an environmental influence on adolescent externalizing after accounting for genetic influences of parents and adolescents. Because the association between parenting and child development originates in the parent, treatment for adolescent externalizing must not only include parents but should also focus on altering their parental style. Thus, findings suggest that teaching parents better knowledge-related monitoring strategies is likely to help reduce externalizing problems in adolescents.
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http://dx.doi.org/10.1111/jcpp.12288DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4280345PMC
February 2015

Accounting for genetic and environmental confounds in associations between parent and child characteristics: a systematic review of children-of-twins studies.

Psychol Bull 2014 Jul 21;140(4):1138-73. Epub 2014 Apr 21.

MRC Social, Genetic & Developmental Psychiatry Centre, Institute of Psychiatry, King's College London.

Parental psychopathology, parenting style, and the quality of intrafamilial relationships are all associated with child mental health outcomes. However, most research can say little about the causal pathways underlying these associations. This is because most studies are not genetically informative and are therefore not able to account for the possibility that associations are confounded by gene-environment correlation. That is, biological parents not only provide a rearing environment for their child, but also contribute 50% of their genes. Any associations between parental phenotype and child phenotype are therefore potentially confounded. One technique for disentangling genetic from environmental effects is the children-of-twins (COT) method. This involves using data sets comprising twin parents and their children to distinguish genetic from environmental associations between parent and child phenotypes. The COT technique has grown in popularity in the last decade, and we predict that this surge in popularity will continue. In the present article we explain the COT method for those unfamiliar with its use. We present the logic underlying this approach, discuss strengths and weaknesses, and highlight important methodological considerations for researchers interested in the COT method. We also cover variations on basic COT approaches, including the extended-COT method, capable of distinguishing forms of gene-environment correlation. We then present a systematic review of all the behavioral COT studies published to date. These studies cover such diverse phenotypes as psychosis, substance abuse, internalizing, externalizing, parenting, and marital difficulties. In reviewing this literature, we highlight past applications, identify emergent patterns, and suggest avenues for future research.
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http://dx.doi.org/10.1037/a0036416DOI Listing
July 2014