Genetic and environmental influences on functional age: a twin study.

Twin analyses were conducted to determine the relative influence of genetic and environmental factors on functional aging. As part of the ongoing Minnesota Twin Study of Adult Development and Aging (MTSADA), measures of 30 demographic, cognitive, physiological, personality, and behavioral variables were available from 140 monozygotic twin pairs and 97 dizygotic twin pairs ranging in age from 27 to 88 years. Functional age was based on a general linear regression model with chronological age as the dependent variable. Stepwise regression determined the subset of variables by MTSADA providing the best prediction of chronological age. Factor analysis of these 12 variables resulted in three factors: physiological measures, cognitive abilities, and processing speed. When entered into, a regression equation, the three factors accounted for 66% of the variance in chronological age. Analysis of twin similarity for components of functional age suggested the relative influence of genetic and environmental factors varies greatly for different components of functional aging. In addition, the genetic and shared environmental influences on the three components were common to all three, while the nonshared environmental influences were specific to each component.