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Purpose: To investigate the association between social isolation and loneliness, how they relate to depression, and whether these associations are explained by genetic influences.Methods: We used data from the age-18 wave of the Environmental Risk Longitudinal Twin Study, a birth cohort of 1116 same-sex twin pairs born in England and Wales in 1994 and 1995. Participants reported on their levels of social isolation, loneliness and depressive symptoms. We conducted regression analyses to test the differential associations of isolation and loneliness with depression. Using the twin study design, we estimated the proportion of variance in each construct and their covariance that was accounted for by genetic and environmental factors.Results: Social isolation and loneliness were moderately correlated (r = 0.39), reflecting the separateness of these constructs, and both were associated with depression. When entered simultaneously in a regression analysis, loneliness was more robustly associated with depression. We observed similar degrees of genetic influence on social isolation (40 %) and loneliness (38 %), and a smaller genetic influence on depressive symptoms (29 %), with the remaining variance accounted for by the non-shared environment. Genetic correlations of 0.65 between isolation and loneliness and 0.63 between loneliness and depression indicated a strong role of genetic influences in the co-occurrence of these phenotypes.Conclusions: Socially isolated young adults do not necessarily experience loneliness. However, those who are lonely are often depressed, partly because the same genes influence loneliness and depression. Interventions should not only aim at increasing social connections but also focus on subjective feelings of loneliness. [ABSTRACT FROM AUTHOR]

Background: Studies assessing sex differences in the associations of psychosocial strain with depression have shown mixed and inconsistent results. Our objective was to examine prospective associations of job strain and family strain with risk of major depressive episode (MDE) among United States workers, as well as assess potential effect modification by sex.Methods: Using data from the nationally representative and population-based Mid-life in the United States (MIDUS) study with a prospective cohort design and a 9-year follow-up period, the effects of job strain and family strain at baseline on risk of MDE within the 12 months prior to the follow-up assessment were examined in 1581 workers (805 men, 776 women) who were free from MDE within the 12 months prior to the baseline survey, by multivariate Poisson regression analysis.Results: After adjustment for relevant covariates, there was evidence for effect modification by sex for the association between job strain and MDE but not for the association between family strain and MDE. Indeed, high job strain was prospectively associated with the risk of MDE (RR and 95% CI = 2.14 [1.14, 4.03]) in men but not in women. Moreover, high family strain was prospectively associated with a higher risk of MDE (RR and 95% CI = 1.57 [1.05, 2.37]) in the whole sample.Conclusion: Family strain was associated with risk of MDE regardless of the sex of a person. In contrast, high job strain may involve an increased risk of developing MDE only in men but not in women. [ABSTRACT FROM AUTHOR]