Age differences in genetic and environmental influences for health from the Swedish Adoption Twin Study of Aging

This cross-sectional study explored the etiology of variability in self-reported health. The sample comprises adult twins participating in the Swedish Adoption/Twin Study of Aging and includes identical (MZ) and fraternal (DZ) twin pairs who have been reared together or reared apart. Two different components of overall health status are analyzed: an index of chronic health problems and self-rated health. Height and weight were included to assess the representativeness of the twin data. Individual differences increased across age for both measures of health, and there were significant age differences in the genetic and environmental etiologies of this variation. Genetic variance showed a twofold increase for chronic illness up until age 70. Environmental influences during adulthood appear important later in life. For self-rated health, genetic effects were important in the older age groups; however, the increase in total variation is predominately due to unique environmental influences. INDIVIDUAL differences in behavioral and biologicalmeasures are substantial and persist throughout life, ac-cording to several studies on aging (Palmore, 1970, 1974; Thomae, 1976). Contrary to traditional views, which hold that declines in physical functioning and health are universal in the later part of the life span, individual differences are pronounced (Bell, Rose, & Damon, 1966; Palmore, 1970