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. This article is part of a Special Collection on Environmental Epidemiology.