Sex and age specific assessment of genetic and environmental influences on body mass index in twins

OBJECTIVE: To assess, by use of a population,based twin register, if there are sex and age differences in genetic and environmental influences on inter-individual variation in BMI among middle-aged and elderly subjects. DESIGN: Twin study. SUBJECTS: 1233 like-sex Danish twin pairs (213 MZ male, 322 DZ male, 280 MZ female, 418 DZ female pairs, age: 46 - 76 years, BWI: 15 - 45 kg/m²). MEASUREMENTS : Self-reported height and weight. METHODS: Proportions of variance due to genetic and environmental factors were estimated from variance-covariance matrices using the structural equation model approach. RESULTS: The most parsimonious explanation of the data was provided by a model that included additive genetic and non-shared environmental factors with the latter fixed to be equal across sex and age. The heritability of BMI was estimated to be 0.46 for males aged 46 - 59 years, 0.61 for males aged 60 - 76 years, 0.77 for females aged 46 - 59 years and 0.75 for females aged 60 - 76 years, CONCLUSION: As in earlier studies, the present one showed a high heritability of BMI throughout adult life, with genetic influences being mainly additive and environmental influences being non-shared, without evidence for major impact of genetic dominance or shared environment. Most twin, family and adoption studies do not suggest important sex or age differences in magnitude of genetic effects, but we found that females had greater heritability than males, and that heritability in males increased by age.