We found moderate to strong evidence for the additive effects of genes influencing BMI change in a nationally representative, ethnically diverse sibling cohort of adolescence followed into young adulthood. These heritability estimates are higher than those from other family studies, (2
) perhaps due to the large variance in BMI change during this critical period of weight gain or to features of our study design, i.e. the sample is primary composed of sibling pairs. The heritability estimates were most similar to those reported by Rice et al, in participants from the Longitudinal Quebec Family Study, where they calculated heritability for BMI change of 37% over a 12-year period. This heritability estimate was mainly driven by correlations between young adult siblings, ranging in age from 19 to 31 years between the two BMI measurements. In comparison to other family studies, this study may have been most similar in age to the Add Health cohort. However, direct comparison of heritability estimates across studies is problematic due to differences in study designs, ascertainment schemes, methods of parameter estimation, and population-specific environmental contributions to the phenotypic variance (16
). The vast majority of literature on heritability is in European samples. Taking advantage of our large, ethnically diverse sample, we found that residual heritability was fairly similar across ethnicity, although power limitations precluded estimation of ethnic-specific interactions.
Household effects are attributable to unmeasured non-genetic factors (e.g., dietary or lifestyle factors) that are shared more closely by members of the same (versus different) household (16
). We found household effects at young adulthood, but not during adolescence perhaps because dietary and physical activity behaviors of adolescents likely mirror parental and sibling behaviors while they live in the same household (17
), but may change as young adults move out and establish their own households. Thus, the differences in household behaviors become more varied as siblings move away from each other and their parents.
Conversely, shared genetic effects between BMI level and change were stronger during adolescence than young adulthood. Research in adult twins similarly shows low genetic correlation between BMI level and change (suggesting little overlap in the genetic variants influencing these phenotypes), which coupled with our findings provide support for distinct genetic effects (7
In summary, our findings suggest that BMI change, particularly in adolescence, may be an important trait for mapping genes related to obesity. In addition, our findings support previous findings of a complex etiology of BMI change, involving genetic and environmental components.