Body weight in the Finnish Twin Cohort.

We estimated genetic and environmental variance of BMI among 7245 non-pregnant MZ and DZ pairs of the same sex from the population-based Finnish Twin Cohort. The contributions of additive genetic effects, shared and non-shared environmental effects on age-adjusted BMI-variance were estimated by LISREL structural equation models. Genetic effects contribute 72% in men and 66.4% in non-pregnant women of total variance, while 27.8% of variance among men and 33.6% among women is due to non-shared environmental effects. Shared environmental effects were nonsignificant (0% for women and 0.2% for men). Similar values were obtained for hereditary and non-shared environmental effects, when shared environmental effects were not included in the model. The inclusion of pregnant women did not substantially change heritability estimates.