Genetic and environmental effects on body mass index during adolescence: a prospective study among Finnish twins.

OBJECTIVE: To study genetic and environmental factors affecting body mass index (BMI) and BMI phenotypic correlations across adolescence. DESIGN: Prospective, population-based, twin cohort study. PARTICIPANTS AND METHODS: We used twin modeling in 2413 monozygotic and same-sex and opposite-sex dizygotic Finnish twin pairs born in 1983-1987 and assessed using self-report questionnaires at 11-12, 14 and 17 years of age. RESULTS: Heritability of BMI was estimated to be 0.58-0.69 among 11-12- and 14-year-old boys and girls, 0.83 among 17-year-old boys and 0.74 among 17-year-old girls. Common environmental effects shared by siblings were 0.15-0.24 among 11-12- and 14-year-old boys and girls but no longer discernible at 17 years of age. Unique environmental effects were 0.15-0.23. Additive genetic factors explained 90-96% of the BMI phenotypic correlations across adolescence, whereas unique environmental factors explained the rest. Common environment had no effect on BMI phenotypic correlations. CONCLUSIONS: The genetic contribution to BMI is strong during adolescence, and it mainly explains BMI phenotypic correlations across adolescence. Common environmental factors have an effect on BMI during early adolescence, but that effect disappears by late adolescence.

Genetic influences on the difference in variability of height, weight and body mass index between Caucasian and East Asian adolescent twins.

OBJECTIVE: Twin studies are useful for investigating the causes of trait variation between as well as within a population. The goals of the present study were two-fold: First, we aimed to compare the total phenotypic, genetic and environmental variances of height, weight and BMI between Caucasians and East Asians using twins. Secondly, we intended to estimate the extent to which genetic and environmental factors contribute to differences in variability of height, weight and BMI between Caucasians and East Asians. DESIGN: Height and weight data from 3735 Caucasian and 1584 East Asian twin pairs (age: 13-15 years) from Australia, China, Finland, Japan, the Netherlands, South Korea, Taiwan and the United States were used for analyses. Maximum likelihood twin correlations and variance components model-fitting analyses were conducted to fulfill the goals of the present study. RESULTS: The absolute genetic variances for height, weight and BMI were consistently greater in Caucasians than in East Asians with corresponding differences in total variances for all three body measures. In all 80 to 100% of the differences in total variances of height, weight and BMI between the two population groups were associated with genetic differences. CONCLUSION: Height, weight and BMI were more variable in Caucasian than in East Asian adolescents. Genetic variances for these three body measures were also larger in Caucasians than in East Asians. Variance components model-fitting analyses indicated that genetic factors contributed to the difference in variability of height, weight and BMI between the two population groups. Association studies for these body measures should take account of our findings of differences in genetic variances between the two population groups.