Does walking for transport contribute to the longitudinal association between neighbourhood walkability and body mass index among mid-to older-aged Australian adults?

Introduction: Studies examining the associations between neighbourhood walkability and adult body weight, as well as the potential mediating role of walking for transport (WfT), are mainly cross-sectional, and longitudinal evidence is lacking. This study investigated the longitudinal association between walkability and body mass index (BMI) and assessed the contribution of WfT to this association. Methods: Data from the HABITAT multilevel longitudinal (2007–16) study of 11,035 middle-aged adult residents of 200 neighbourhoods in Brisbane, Australia, were used. Neighbourhood walkability within a 1 km network buffer around residents’ homes was objectively measured using land use mix, street connectivity, and residential density, and BMI was measured using self-reported height and weight. At each wave (2007, 2009, 2011, 2013 and 2016), respondents estimated the duration (minutes) of WfT in the previous 7 days, which was modelled as both a binary and continuous measure. Mixed-effects regression models were used to examine whether any WfT (yes/no) contributed to the association between walkability and BMI, and generalised structural equation modelling was used to estimate the mediating effect of minutes WfT on this relationship. The models were adjusted for age, sex, education, occupation, household income, neighbourhood disadvantage, survey year, and residential self-selection. Results: Living in a walkable neighbourhood was significantly associated with greater odds of engaging in any WfT and more minutes of walking, and each measure of walking was associated with a lower BMI. Any WfT made no apparent contribution to the association between walkability and BMI, whereas minutes spent walking explained approximately 7.8 % of this relationship. Conclusions: Walkable neighbourhoods may help reduce BMI at the population and individual levels by promoting WfT. Creating walkable communities to support WfT holds the potential for maintaining a healthy body weight and preventing the onset of weight-related chronic conditions such as diabetes and cardiovascular disease.