Genetic and environmental factors underlying parallel changes in body mass index and alcohol consumption: a 36-year longitudinal study of adult twins

Background The genetic and environmental underpinnings of simultaneous changes in weight and alcohol consumption are poorly known. Objective We sought to quantify the environmental and genetic components underlying parallel changes in weight and alcohol consumption, and to investigate potential covariations between them. Methods The analysis comprised 4461 adult participants (58% women) from the Finnish Twin Cohort. Four measures of alcohol consumption and body mass index (BMI) were available over a 36-year follow-up. Trajectories of each trait were described by growth factors, defined as intercepts (i.e., baseline) and slopes (i.e., change over follow-up), using Latent Growth Curve Modeling. Growth values were used for male (190 MZ pairs, 293 DZ pairs) and female (316 MZ pairs, 487 DZ pairs) same-sex complete twin pairs in multivariate twin modeling. The variance and covariance of growth factors were then decomposed into genetic and environmental components. Results The baseline heritabilities were similar in men (BMI: h 2 =79%; alcohol consumption: h 2 =49%) and women (h 2 =77%; h 2 =45%). Heritabilities of BMI change were similar in men (h 2 =52%) and women (h 2 =57%), but higher in men for change in alcohol consumption (h 2 =45%) than in women (h 2 =31%). Significant genetic correlations between BMI at baseline and change in alcohol consumption were observed in both men (r =-0.17(95% Confidence Interval: -0.29,-0.04)) and women (r=-0.18(−0.31,-0.06)). The genetic components of baseline and longitudinal change were correlated for both BMI and alcohol consumption with sex differences. Non-shared environmental factors affecting changes in alcohol consumption and BMI were correlated in men (r=0.18(0.06,0.30)). Among women, non-shared environmental factors affecting baseline alcohol consumption and the change in BMI were correlated (r=-0.11(−0.20,-0.01)). Conclusions We provide evidence of genetic correlations between BMI and change in alcohol consumption. Independent of genetic effects, change in BMI and change in alcohol consumption covary.