Genetic effects on physical health: lower at higher income levels.

Given the robust finding that people in higher income groups tend to experience better physical health, there is interest in identifying mechanisms underlying this gradient. Using a nationwide sample of 719 twin pairs from the National Survey of Midlife Development in the United States, we investigated the possibility that gene-environment interaction underlies the income-health gradient. We observed that genetic variance associated with 2 measures of physical health, number of chronic illnesses and body mass index, each declined significantly with increasing income. This interaction effect could not be removed by adjusting income for the presence of health insurance coverage and education, suggesting that the interaction is not simply a result of differences in levels of those characteristics with income.