Local descriptive norms for overweight/obesity and physical inactivity, features of the built environment, and 10-year change in glycosylated haemoglobin in an Australian population-based biomedical cohort

Descriptive norms vary between places. Spatial variation in health-related descriptive norms may predict individual-level health outcomes. Such relationships have rarely been investigated. This study assessed 10-year change in glycosylated haemoglobin (HbA1c) in relation to local descriptive norms for overweight/obesity (n = 1890) and physical inactivity (n = 1906) in models accounting for features of the built environment. HbA1c was measured three times over 10 years for a population-based biomedical cohort of adults in Adelaide, South Australia. Environmental exposures were expressed for cohort participants using 1600 m road-network buffers centred on participants' residential address. Local descriptive norms (prevalence of overweight/obesity [body mass index ≥25 kg/m(2)] and of physical inactivity [<150 min/week]) were aggregated from responses to a separate geocoded population survey. Built environment measures were public open space (POS) availability (proportion of buffer area) and walkability. Separate sets of multilevel models analysed different predictors of 10-year change in HbA1c. Each model featured one local descriptive norm and one built environment variable with area-level education and individual-level covariates (age, sex, employment status, education, marital status, and smoking status). Interactions between local descriptive norms and built environment measures were assessed. HbA1c increased over time. POS availability and local descriptive norms for overweight/obesity and physical inactivity were each associated with greater rates of HbA1c increase. Greater walkability was associated with a reduced rate of HbA1c increase, and reduced the influence of the overweight/obesity norm on the rate of increase in HbA1c. Local descriptive health-related norms and features of the built environment predict 10-year change in HbA1c. The impact of local descriptive norms can vary according to built environment features. Little researched thus far, local descriptive norms may play an important role in the evolution of HbA1c and thus cardiometabolic risk, over time. Further empirical research on local descriptive norms is necessary to understand how residential environments shape chronic disease risk.