Longitudinal association between walkability and physical activity in twins.

Introduction: Research has focused on the built environment (e.g., neighborhood walkability) that supports or hinders physical activity because it is potentially modifiable. This study investigated associations between changes in neighborhood walkability and changes in physical activity in an adult twin cohort.

Methods: Longitudinal data (2009-2020) in 7,439 identical and fraternal twins comprising 2,800 complete pairs from a community-based Registry was analyzed. Participants were free of mobility limitations and resided at their current residential location for at least 1-year. A series of "phenotypic" (non-genetically informed) models were used to test the effect of walkability change on change in physical activity. These were re-estimated in a series of "quasi-causal" models by leveraging the genetically-informed nature of the twin design to test the effect of walkability change on change in physical activity while controlling for genetic and shared environmental confounds.

Results: Change in neighborhood walkability was associated with change in neighborhood walking, but not moderate-to-vigorous physical activity, which held after controlling for genetic and shared environmental confounding, plus standard demographic covariates, length of follow-up, and moving status. A 1-unit increased change in neighborhood walkability was associated with a 2.7-minute increased change in neighborhood walking per week, independent of familial confounds and covariates. Moving to a neighborhood that is 5.5 units greater in walkability could increase neighborhood walking by about 15 minutes per week.

Conclusions: This study supports a "quasi-causal" relationship between changes in neighborhood walkability and changes in neighborhood walking, extending previous cross-sectional findings in the same twin cohort by establishing temporality.