FAMILIAL AGGREGATION OF SEVEN YEAR CHANGES IN HUMAN ADIPOSITY

There is consistent evidence from cross-sectional studies for significant familial resemblance in body fatness; however, longitudinal familial resemblance in adiposity remains unclear. The purpose of this study was to determine the familial aggregation in baseline and 7-y changes in adiposity in the Canadian population. Measures of adiposity were collected on 655 females and 661 males 7–69 y of age who participated in both the 1981 Canada Fitness Survey and 1988 Campbell's Survey of Well Being. The sample was distributed across 521 nuclear families with a mean family size of 2.5 people. Four indicators of adiposity were measured and used in change score calculations: body mass (kg); body mass index, BMI, (kg/m2); sum of 5 skinfolds, SF5, (mm); and waist circumference, WC, (mm). Data were adjusted for age in both the mean and variance by regression in four sex-by-generation groups (father, mother, son, daughter) and standardized to zero mean and unit variance. Familial correlations and maximal heritabilities were determined from path analysis using SEGPATH software. The maximal heritabilities for baseline measures of body mass, BMI, SF5 and WC were 56%, 39%, 41% and 39%, respectively, while the estimates for the 7-y change scores in body mass, BMI, SF5 and WC were 23%, 14%, 12% and 45%, respectively. The estimates of maximal heritability suggest that familial factors explain more of the variance in baseline body mass, BMI and SF5 than changes over time; however, the change in WC had a comparable heritability. The finding that familial factors appear to be more important cross-sectionally than longitudinally suggests that other lifestyle factors may be important determinants of changes in adiposity. This research was supported by the Heart and Stroke Foundation of Canada.