Tobacco consumption in Swedish twins reared apart and reared together

Background: Prior studies of twins reared together suggest that regular tob acco use (RTU) is substantially heritable. However, strong social influence s on RTU might have biased these results. Methods: We examine the self-report lifetime history of RTU in members of 7 78 male-male and female-female twin pairs, raised together and apart, born from 1890 to 1958 and ascertained through the population-based Swedish Twin Registry. Results: In men, the pattern of twin resemblance for RTU suggested both gen etic and rearing-environmental effects, which, in the best-fit biometrical model, accounted for 61% and 2096 of the variance in liability to RTU, resp ectively. For women, overall results were hard to interpret, but became cle arer when divided by birth cohort. In women born before 1925, rates of RTU were low and twin resemblance was environmental in origin. In later cohorts , rates of RTU in women increased substantially, as did heritability. For w omen born after 1940, heritability of RTU was similar to that seen in men ( 63%). Conclusions: Genetic factors play an import-ant etiologic role in RTU. In w omen, the impact of genetic factors increased in more recent cohorts, sugge sting that, as social restrictions on female tobacco use relaxed over time, heritable influences increased in importance.