Longitudinal relationships of the neighbourhood built environment with cardio-metabolic health

Neighbourhood built environments may have the potential to impact residents’ cardiometabolic health through physical activity. This Thesis aims to advance the understanding of such potential impacts. This Thesis consists of three published peer-reviewed studies. Study One, a systematic review and meta-analyses of longitudinal studies, found strong evidence for longitudinal relationships of built environment attributes with cardiometabolic health among adults. In particular, it found strong evidence for relationships of higher walkability with reduced risks of obesity, type 2 diabetes and hypertension. This systematic review has been published in Obesity Reviews. Two empirical studies were designed to address the gaps identified in the systematic review. These studies were conducted using the Australian Diabetes, Obesity and Lifestyle (AusDiab) study data, which were collected from a national cohort at three time points between 1999 and 2012. The outcomes examined in the empirical studies were 12-year changes in eight cardio-metabolic risk markers: waist circumference; weight; systolic and diastolic blood pressure; fasting and 2-hr postload plasma glucose; high-density lipoprotein cholesterol; and triglycerides. Built environmental attributes for AusDiab study participants were calculated using geographic information systems as an original work of this Thesis. The analytical sample consisted of participants who provided 12-year followup data and did not change their residence during the study period. One gap identified in the systematic review was that most longitudinal studies examined environmental attributes (typically composite measures such as walkability) assessed at one time point, disregarding environmental changes. To address this gap, Study Two examined the relationships of neighbourhood population density increases (densification) on changes in cardio-metabolic risk markers. Densification was calculated using the population density values measured within a 1-km straight-line buffer at three time points in concordance with the AusDiab data collection points. Analysing data from 2,354 eligible participants, higher densification was found related to smaller increases in obesity markers, but it was adversely related to blood pressure and lipid changes. This study has been published in the Journal of the American Heart Association. Study Three investigated the potential mediating role of physical activity (baseline and change) in the relationships between walkability and changes in cardio-metabolic risk markers, as a lack of studies rigorously examining underlying mechanisms of these relationships was another gap identified. For physical activity, self-reported time spent in moderate-to-vigorous physical activity (including walking) was used. A walkability index (consisting of residential density, intersection density, and destinations density) was calculated, within a 1-km street-network buffer using geospatial data sourced around the second follow-up of AusDiab. Analyses of data from 2,023 participants found that higher walkability was related to higher baseline physical activity, which, in turn, was related to smaller increases in obesity markers. There was no evidence for a relationship of higher walkability with a change in physical activity. This study has been published in the International Journal of Behavioral Nutrition and Physical Activity. Collectively, this Thesis adds evidence for potential long-term impacts of the neighbourhood built environment on adult residents’ cardio-metabolic health. In particular, higher walkability and higher densification may have protective effects against obesity risk over time. This Thesis also found evidence suggesting that physical activity may partly explain the potential long-term protective effect of higher walkability against obesity risk. However, there were also some unexpected findings, for instance, potential adverse impacts of higher densification on blood pressure and lipid, which warrants further investigation. The Thesis findings support the potential utility of environmental initiatives to reduce the burden of obesity at the population level through enhancing physical activity. To further advance understanding of the impacts of the built environment on cardio-metabolic health, future research needs to examine diverse built environmental attributes, investigate a broader range of cardio-metabolic health outcomes, and examine multiple pathways between the built environment and cardio-metabolic health.