FAMILIAL AGGREGATION OF PHYSICAL ACTIVITY LEVELS

The familial aggregation of four physical activity (PA) phenotypes was investigated in 696 subjects from 200 families of the Quebec Family Study. The mean age of offspring and parents was 27 and 53 years, respectively. Current level of PA (total PA, inactivity and strenuous PA) was obtained using a three-day diary and PA during the past year was estimated by questionnaires. The PA phenotypes were adjusted for age and sex using regression procedures and the residuals were used for analyses. An ANOVA performed on the PA phenotypes revealed that there were 1.40 to 1.52 times more variation in PA levels between families than within families (p from 0.001 to 0.0001), suggesting that PA levels tend to aggregate in families. Familial resemblance was further studied by fitting a general familial correlation model (SEGPATH) and eleven reduced models to the data. For each PA phenotype, the spouse correlation was found to be higher than the parent-offspring and sibling correlations. Maximal heritabilities, adjusted for the degree of spouse resemblance, reached 25%, 16%, 19% and 17% for physical inactivity, strenuous PA, total PA and weekly time spent on the main activity during the previous year, respectively. These results suggest that PA level in this Canadian urban population is characterized by a significant degree of familial resemblance. The pattern of familial correlations suggests that shared familial environmental factors are more important than genetic factors to explain the familial resemblance of activity level. Supported by Academy of Finland, Finnish Ministry of Education and MRC of Canada.