Age and Sex Differences in Genetic and Environmental Factors for Self-Rated Health.

OBJECTIVES Self-rated health has been shown to be a predictor for future health status and mortality. The purpose of this study was to investigate age-group and sex differences in genetic and environmental sources of variation for self-rated health. METHODS A sample of twins from the Swedish Twin Registry participated in a computer-assisted telephone interview with assessment of self-rated health. Structural equation model analyses on 1,243 complete twin pairs provided estimates of genetic and environmental components of variance. RESULTS Individual differences primarily reflected individual specific environmental influences at all ages. The increase in total variance across age groups was primarily due to genetic influences in the age groups 45--74 years and greater environmental influences in the oldest age group (>74). No significant sex differences were found in variance components. DISCUSSION Genetic variance in the two middle age groups (45--74) could reflect genetic susceptibility to age-dependent illnesses not yet expressed in the youngest group. The findings suggest that it might be more fruitful to explore the origins of individual differences for self-rated health in the context of an individual's age and birth cohort rather than in the context of sex.