Background Persistent inequalities in obesity-related health outcomes may be partly due to unequal distribution of resources in local built environments. For example, differential neighbourhood access to physical activity (PA) facilities or exposure to unhealthy food environments may influence health behaviours and ultimately be reflected in uneven population distributions of overweight and obesity. Despite much research, evidence on health effects of neighbourhood environments remains inconclusive, making it difficult to generalise to suitable interventions, if indeed intervention is warranted.

Methods Using cross-sectional data from ~2 70 000 adults aged 40–70 from the UK Biobank cohort residing across England and Wales, including linked person-centred environmental data, we examined whether features of the fast food and PA environments near an individual’s place of residence were independently associated with measures of adiposity. We also constructed a composite exposure measure to examine the PA and fast food environments operating together, classifying people’s neighbourhoods on a scale of obesogenicity, from high (limited PA facilities and close to a fast food outlet) to low (many PA facilities and far from a fast food outlet). Multilevel models were used to account for clustering due to an area-based sampling design and were adjusted for potential confounding effects of individual and area-level variables, including each exposure on the other.

Results Considered separately we found that greater density of PA facilities and greater distance to the nearest fast food outlet were independently associated with smaller waist circumference (WC) e.g. having ≥6 formal PA facilities within a 1 km street network distance of home was associated with 0.91 cm lower WC (95% CI: 0.32–1.49) than having no nearby PA facilities, and living >2 km from the nearest fast food outlet was associated with 0.42 cm lower WC than living within 500 m (95% CI: 0.11–0.72). Similar patterns were observed for other adiposity outcome measures. Preliminary results from ongoing analyses using the composite exposure measure indicate a possible dose response of WC to increasing combined neighbourhood obesogenicity. A series of sensitivity and other additional analyses currently underway, including the use of propensity scores, will also be presented to explore the possibility that residual confounding may explain the findings.

Conclusion Combining a very large sample with wide geographical coverage and robust statistical methods we sought improved clarity on the potential health impact of two built environment exposures, and present evidence suggesting that improving neighbourhood access to PA facilities and minimising proximity to fast food outlets may help reduce adiposity in the UK mid-aged adult population.