Higher Perceived Life Control Decreases Genetic Variance in Physical Health: Evidence From a National Twin Study.

Physical health has been linked consistently with both income and sense of control, and the authors previously demonstrated that genetic variation in physical health measures decreased with increasing income (see W. Johnson R. F. Krueger, 2004). Using a nationwide sample of 719 twin pairs from the MacArthur Foundation National Survey of Midlife Development in the United States, in this study the authors show that genetic variation in physical health measures (number of chronic illnesses and body mass index) also decreases with increasing sense of control. The authors integrate findings for income and control by demonstrating an interaction between genetic influences on sense of control and income in explaining physical health. They hypothesize that the mechanism underlying the interaction is the known biological relationship between metabolic efficiency and adaptation to stressful environments. Physical health has consistently been linked with income, wealthier people being healthier. The relationship holds over time, in a variety of geographic settings, and for almost every disease and condition (Adler et al., 1994). The association is monotonic across the full range of income; it is not limited to a comparison of those with incomes below and above poverty levels. The relationship