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.