Genetic and Environmental Associations Between Depressive Symptomatology and Loneliness in Adulthood.

The conceptual and symptom overlap between depression and loneliness is so strong that depressive symptom rating scales often include measures of loneliness, and their linear association ranges between .40 and .68. Despite these findings, few genetically informed studies have investigated the genetic and environmental association between them. We tested the degree to which depressive symptomatology and loneliness are correlated genetically and environmentally, and whether the environmental correlation in men is larger than in women. In this study, we used 428 individual twins (229 MZ twins and 187 DZ twins) from 266 families (139 MZ families and 127 DZ families) from the Louisville Twin Study (MAge = 48.17; 56% female). Loneliness was measured using the UCLA Loneliness Scale (3 items), and depressive symptomatology was measured using the Center for iologic Studies Depression Scale. Statistical analysis included twin correlations and a correlated factors model. Results indicate that the genetic correlation between loneliness and depressive symptomatology is .47 [.95CI: .16-.78] and the nonshared environmental correlation is .28 [.95CI: .12-.43]. No sex differences were observed. In mid-adulthood, a little less than half of the genetic variance associated with depressive symptomatology is also associated with loneliness. Nonshared environmental factors underlying depressive symptomatology account for approximately 54.4% of the strong association with loneliness, too. These results are similar to bivariate estimates reported in a previous studies of young adulthood, suggesting that across adulthood, the contribution of genetic and non-shared environmental factors to the association between loneliness and depression is constant.