Genetic and environmental influences on social support in later life: a longitudinal analysis

The present study assessed the etiology of individual differences in social support over a six-year period. The availability of friend support, family support, and the perceived adequacy of the social support network was assessed three times using identical and same-gender fraternal twins reared together and reared apart from the Swedish Adoption/Twin Study of Aging. Results are based on the pairwise responses at the three occasions of measurement (labeled Q1, Q2, and Q3): 462 pairs at Q1 (assessed October 1984), 474 pairs at Q2 (October 1987), and 431 pairs at Q3 (October 1990). The longitudinal phenotypic correlations (ranging from .49 to .77) indicate that social support is a moderately stable characteristic. Qualitative genetic model-fitting analyses resulted in significant heritability estimates for the social support measures at all three measurement occasions. Results also indicate considerable stability in genetic effects across measurement occasions, with genetic correlations ranging from .65 to .97. Nonshared environmental influences were substantial contributors to social support, but were less stable across the measurement occasions, with correlations ranging from .07 to .52.