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Although social and intellectual engagement have been consistently associated with late-life functioning, rather than true causation, these associations may reflect the experiential choices of high functioning individuals (i.e., selection effects). We investigated the association of social activity with late-life physical functioning, cognitive functioning, and depression symptomatology using data from 1112 pairs of like-sex twins who participated in the Longitudinal Study of Aging Danish Twins. Consistent with previous research, we found that social activity was significantly correlated with overall level of physical functioning, cognitive functioning, and depression symptomatology. We also found that social activity was significantly and moderately heritable (estimate of .36), raising the possibility that its association with late-life functioning might reflect selection processes. Further, social activity did not predict change in functioning and in monozygotic twin pairs discordant on level of social activity, the more socially active twin was not less susceptible to age decreases in physical and cognitive functioning and increases in depression symptomatology than the less socially active twin. These results are interpreted in the context of the additional finding that nonshared environmental factors, although apparently not social activity, are the predominant determinant of changes in late-life functioning. [ABSTRACT FROM AUTHOR]

The Danish Twin Registry is the oldest national twin register in the world, initiated in 1954, and, by the end of 2005, contained more than 75,000 twin pairs born in the between 1870 and 2004. The Danish Twin Registry is used as a source for studies on the genetic influence on normal variation in clinical parameters associated with the metabolic syndrome and cardiovascular diseases, clinical studies of specific diseases, and aging and age-related health problems. The combination of survey data, clinical data and linkage to national health-related registers enables follow-up studies of both the general twin population and twins from clinical studies. This paper summarizes the newest extension of the register and gives examples of new developments and phenotypes studied. [ABSTRACT FROM AUTHOR]