A CROSS-SECTIONAL EXAMINATION OF HEIGHT, WEIGHT, AND BODY-MASS INDEX IN ADULT TWINS

A cross-sectional twin design was used to study the developmental natu re of genetic and environmental influences on height, weight, and body mass index. The sample of same-sex adult male and female twins consis ted of 586 monozygotic and 447 like-sex dizygotic twin pairs aged 18 t o 81 years. Means and variances suggested normative age differences fo r all three physical variables. Biometrical model-fitting with maximum likelihood methods of parameter estimation indicated that the general best-fitting model across the age groups for height, weight, and body mass index was one in which the genetic effects were additive and the environmental effects were from nonshared, idiosyncratic experiences. The best-fitting cross-sectional biometrical model for height, weight , and body mass index indicated that additive genetic variance remaine d stable while nonshared environmental variance increased with age. Th is increase in environmental variance but stable genetic variance resu lted in decreasing heritability with age for height (heritability rang ing from 0.89 in the youngest group to 0.87 in the oldest), weight (he ritability ranging from 0.86 in the youngest group to 0.70 in the olde st), and body mass index (heritability ranging from 0.82 in the younge st group to 0.63 in the oldest).