Genetic and early environmental components in sociodemographic influences on adult body fatness.

OBJECTIVE To explore genetic and environmental contributions to the influence of parental social class and region of upbringing on adult human fatness. DESIGN Survey of sample of adults who had been adopted in childhood to relate their body mass index to sociodemographic variables in a series of multiple linear regression analyses. SUBJECTS 4643 Subjects traced from a register of 5455 non-familial adoptees registered in 1924-47, of whom 3651 gave details of current height, weight, and occupation. The final sample totalled 2015 adoptees for whom there was also information on their region of upbringing and on the social class of their adoptive and biological fathers. MAIN OUTCOME MEASURES Age, sex, body mass index, social class (of adoptee and adoptive and biological father), and geographical region. RESULTS There was a significant inverse relation of adoptees' body mass index with their own social class and that of both their biological and adoptive fathers. Adoptees raised in provincial areas had a significantly greater body mass index than did those raised in Copenhagen. A multivariate regression model, including age, sex, and social class of the adoptee, confirmed the significant independent influence of the social class of both adoptive and biological fathers and of region of rearing on adoptees' body mass index. CONCLUSION Both familial environmental and genetic factors contribute to the relation of parental social class to adult fatness, and they are partly independent of the effect of an individual's own social class. The influence of region of upbringing on adult fatness is of environmental origin and is independent of social class characteristics.