Twin similarity for residential location and health outcomes in late adulthood

Socioeconomic status (SES) is one of the most robust predictors of health. The source of SES–health associations is heavily debated; one approach is investigating neighbourhood-level environmental characteristics. Challenges include selection effects and the possibility of reverse causation: people choose their neighbourhoods. Longitudinal twin research can overcome these issues by assessing location choice over time as well as twin similarity; however, few existing twin studies have incorporated neighbourhood-level data, and even fewer focus on ageing. Using longitudinal data from the Swedish Adoption/Twin Study of Aging, the current study examined the impact of location at various points in life. Location at birth and in 1993 were available for 784 participants. Birth years ranged from 1926 to 1948; mean age in 1993 was 54.45 (range: 35–67). Thirty-nine per cent of the sample had moved to a different county between birth and midlife: individuals who moved had significantly higher parental SES and had achieved significantly higher education. Moreover, identical twin concordance for geographic mobility (77 per cent) was significantly higher than fraternal twin concordance (65 per cent), indicating a modest but statistically significant genetic contribution. Within discordant identical twin pairs, the twin who moved averaged a better score on a measure of functional ageing in late adulthood than the twin who stayed. Moderation models suggest higher heritability for self-rated health, subjective SES and functional ageing for twins who lived in urban versus rural environments.