Matthews et al. (2016)

Social isolation, loneliness and depression in young adulthood: a behavioural genetic analysis.

Background information: Social isolation is a state of estrangement, in which social connections are limited or absent. Loneliness is a subjective feeling of distress, arising when social connections are perceived to be inadequate or unfulfilling. Although they tend to occur together, they can also be experienced independently of one another: isolated individuals do not necessarily feel lonely, nor does an abundance of social connections mean a person does not feel lonely. So, although there is overlap between the two conditions, there are important conceptual distinctions between them. This research therefore measures both.

Loneliness is a stronger risk factor for depression than is social isolation. Although the prevalence of loneliness varies with age, its association with depression remains stable across the lifespan. To date, however, no behavioural genetic studies have been carried out to estimate the extent to which the associations between isolation, loneliness and depression are explained by common genetic or environmental influences.

Aim: To investigate the association between social isolation and loneliness, how they relate to depression, and whether these associations are explained by genetic influences.

Method: The researchers 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. They analysed the data to test the separate associations of isolation and loneliness with depression, using a test of correlation. After this, the results for each twin were compared for a correlation in these associations and in depression, to determine if a difference in correlation between DZ and MZ twins suggests a genetic influence.

Results: Social isolation and loneliness were moderately correlated (r = 0.39), reflecting the separateness of these constructs, and both were associated with depression, with loneliness more strongly associated with depression. Genetic correlations of 0.65 between isolation and loneliness and 0.63 between loneliness and depression indicated a strong role of genetic influences in their co-occurrence.

Conclusion: Socially isolated young adults do not necessarily experience loneliness. However, those who are lonely are often depressed, partly because the same genes seem to influence loneliness and depression. Interventions should not only aim at increasing social connections but also focus on subjective feelings of loneliness.

Evaluation:

Strengths: By isolating the variables of loneliness, isolation and depression, the researchers were able to measure their individual and co-occurring effects on the MZ and DZ twins and identify the possible level of heritability. This was a well-designed analysis of data.

Limitations: There is little agreement as to the best measure of isolation, and some measures may be more appropriate than others depending on the age group under investigation. In this study of 18 year olds, many of the measures - such as marital status or living alone - were inappropriate, so the researchers used ‘low social support’ as the measure of social isolation. However, social support is not the only feature of social relationships that may have implications for mental health outcomes. Furthermore, there may be individual differences in the way participants self-report and rate the amount of support available to them.