Behavioral Genetics, Health, and Aging

A recurring observation from studies of health in the elderly is the pervasiveness of individual differences. For many health-related endpoints, total variation appears to increase across age group; however, few longitudinal studies have reported whether these age differences reflect true age-related changes. There are a growing number of twin studies of aging that provide some insight, at least cross-sectionally, into the nature of individual differences in health. Increases in total variance most often reflect increases in environmental sources of variance. Covariation among traits reflects both genetic and environmental mediation, dependent on the sex of the sample and the measures of interest. Co-twin control approaches have been successful in exploring the role of environmental influences as risk factors for poor health. The most serious limitation to these studies is the lack of longitudinal information to disentangle survival and selection effects from aging.