Association between neighborhood walkability and physical activity in a community-based twin sample

We investigated associations between neighborhood walkability and physical activity using twins (5477 monozygotic and same-sex dizygotic pairs) as “quasi-experimental” controls of genetic and shared environment (familial) factors that would otherwise confound exposure-outcome associations. Walkability comprised intersection density, population density, and destination accessibility. Outcomes included self-reported weekly minutes of neighborhood walking and moderate-to-vigorous physical activity (MVPA) and days per week using transit services (eg, bus, commuter rail). There was a positive association between walkability and walking, which remained significant after controlling for familial and demographic factors: a 1% increase in walkability was associated with a 0.42% increase in neighborhood walking. There was a positive association between walkability and MVPA, which was not significant after considering familial and demographic factors. In twins with at least 1 day of transit use, a 1-unit increase in log (walkability) was associated with a 6.7% increase in transit use days; this was not significant after considering familial and demographic factors. However, higher walkability reduced the probability of no transit use by 32%, considering familial and demographic factors. Using a twin design to improve causal inference, walkability was associated with walking, whereas walkability and both MVPA and absolute transit use were confounded by familial and demographic factors.