Gene–Environment Interplay Between Residential Walkability and BMI : A Finnish Twin Study

OBJECTIVE: BMI is influenced by both genetic and environmental factors, including features of the obesogenic environment such as walkability. This study investigated the interplay between residential walkability, genetics, and BMI among 4312 individuals from two Finnish twin cohorts (mean age: 43). METHODS: Residential walkability was quantified using a composite index including built and natural environmental features. RESULTS: Multiple linear regression, adjusted for sociodemographic factors, showed that higher walkability was associated with lower BMI (coefficient: -0.02, 95% CI: -0.04, -0.01), but pairwise twin analyses indicated that this association was not independent of genetic and early shared environmental influences. Univariate twin modeling revealed that additive genetic effects accounted for 22% of the variation in walkability when participants were middle-aged. Bivariate moderation twin modeling showed that the additive genetic influence on BMI was significantly stronger among individuals living in areas with average or moderately low residential walkability. The unique environmental component played a larger role among those living in areas with either very low or very high residential walkability. CONCLUSIONS: These findings underscored the complex gene-environment interplay between walkability and BMI. While genetic susceptibility cannot be modified, public health strategies that focus on the obesogenic environment, such as improving walkability, may still help mitigate obesity risk.