Local descriptive norms, smoking and body mass index in the Netherlands: Population-based study between 2012 and 2020.

Understanding the relationship between local health norms and individual behaviors can inform policies to reduce neighbourhood health inequalities. This study examines how local descriptive norms, measured as the prevalence of smoking and overweight in neighbourhoods, relate to individual smoking and body mass index (BMI) over time. We used data from the Dutch Lifelines cohort and an existing policy instrument, SMall Area estimates for Policymakers (SMAPs), to estimate neighbourhood smoking and overweight prevalence in the Northern Netherlands (2012, 2016) and changes between these years. These estimates were linked to individual smoking and BMI in 2020 and to changes from 2016 to 2020. Generalized Linear Models were used to estimate the probability of individual smoking and overweight related to (changes) in the neighbourhood prevalence of smoking and overweight, controlling for prior health (behaviors) and socio-demographic factors. Generalized Additive Models were fitted to assess non-linearity. The sample included 31,753 individuals across 957 neighbourhoods. A five percent higher prevalence of neighbourhood smoking in 2016 was associated with an increased relative risk of individual smoking in 2020 (RR = 1.13, 95 %CI 1.04-1.23). A five percent higher prevalence of overweight in 2016 was related to a nearly half-point higher individual BMI in 2020 (B = 0.47, 95 %CI 0.40-0.55). Non-linear associations were observed between neighbourhood overweight prevalence (2012, 2016) and individual BMI (2020), with steeper BMI increases in neighbourhoods where around half of the residents were overweight. For smoking the relationship was linear. Neighbourhood prevalence was not related to individual changes in smoking and BMI from 2016 to 2020. Considering local descriptive norms might offer opportunities to tackle neighbourhood inequalities in health more effectively.