Body fat and mobility are explained by common genetic and environmental influences in older women

In older adults, mobility limitations often coexist with overweight or obesity, suggesting that similar factors may underlie both traits. This study examined the extent to which genetic and environmental influences explain the association between adiposity and mobility in older women. Body fat percentage (bioimpedance test), walking speed over 10 m, and distance walked in a 6-min test were evaluated in 92 monozygotic (MZ) and 104 dizygotic (DZ) pairs of twin sisters reared together, aged 63-76 years. Genetic and environmental influences on each trait were estimated using age-adjusted multivariate genetic modeling. The analyses showed that the means (and s.d.) for body fat percentage, walking speed, and walking endurance were 33.2+/-7.3%, 1.7+/-0.3 m/s and 529.7+/-75.4 m, respectively. The phenotypic correlation between adiposity and walking speed was -0.32 and between adiposity and endurance it was -0.33. Genetic influences explained 80% of the association between adiposity and speed, and 65% of adiposity and walking endurance. Cross-trait genetic influences accounted for 12% of the variability in adiposity, 56% in walking speed, and 34% in endurance. Trait-specific genetic influences were also detected for adiposity (54%) and walking endurance (13%), but not speed. In conclusion, among community-living older women, an inverse association was found between adiposity and mobility that was mostly due to the effect of shared genes. This result suggests that the identification of genetic variants for body fat metabolism may also provide understanding of the development of mobility limitations in older women.