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 t here are sex and age differences in genetic and environmental influenc es 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: 4 6-76 years, BMI: 15-45 kg/ml(2)). MEASUREMENTS : Self-reported height and weight. METHODS: Proportions of variance due to genetic and enviro nmental factors were estimated from variance-covariance matrices using the structural equation model approach. RESULTS: The most parsimoniou s explanation of the data was provided by a model that included additi ve 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 ye ars. CONCLUSION: As in earlier studies, the present one showed a high heritability of BMI throughout adult life, with genetic influences bei ng mainly additive and environmental influences being non-shared, with out evidence for major impact of genetic dominance or shared environme nt. Most twin, family and adoption studies do not suggest important se x or age differences in magnitude of genetic effects, but we found;hat females had greater heritability than males, and that heritability in males increased by age.