UNTANGLING GENETIC INFLUENCES ON SMOKING, BODY-MASS INDEX AND LONGEVITY - A MULTIVARIATE STUDY OF 2464 DANISH TWINS FOLLOWED FOR 28 YEARS

A multivariate twin study was conducted in order to evaluate to what e xtent smoking, BMI and longevity are influenced by common genetic fact ors. The study was based on a 28-year follow-up of a sample of 2464 Da nish twins who were born in the period 1890-1920 and who answered a qu estionnaire, including requests for information on smoking status, hei ght and weight, in 1966. By 1994, approximately 2/3 of the sample had died. To compensate for the right-censoring, age at death was imputed for twins who were still alive by using survival analysis; all living subjects were more than 73 years old (mean 80 years, SD 5) in 1994. Pr oportions of covariance resulting from genetic and environmental facto rs in common and unique to the three traits were estimated from covari ance matrices using the structural equation model approach. The study found no evidence for a substantial impact of common genetic factors o n smoking, BMI and longevity. This suggests that only a small fraction of the genetic influences on longevity is mediated via a genetic infl uence on smoking and BMI and, furthermore, that it is unlikely that th e associations between smoking and mortality and between BMT. and mort ality are confounded by common genetic factors.