Year

2020

Degree Name

Doctor of Philosophy

Department

School of Health and Society

Abstract

Background: The growing burden of type 2 diabetes mellitus (T2DM) suggests that past efforts via lifestyle modification and weight-loss programs have not yielded population-level gains. Evidence indicates that the environment where a person lives and interacts may influence T2DM. However, much of the current data on the association between the built environment and T2DM comes from cross-sectional studies and are prone to residential self-selection bias. Furthermore, the role of some environmental characteristics and the mechanisms underlying such a relationship remains less clear. These limitations make the current evidence of less use in informing policies.

Aim: This research aims to better understand the influence of the built environment on T2DM by addressing some gaps identified in the literature. This thesis investigates the associations between perceived built environment characteristics and T2DM incidence, the pathways through which the identified associations occur, and the modification of the associations by other factors. The findings are expected to help inform policies aimed to build health-enhancing communities and reduce health inequalities.

Methods: This thesis used the longitudinal data of the 45 and Up Study. Data of 36,224 individuals (43.8% men and 56.2% women) aged 45 years and above from the population of New South Wales, Australia, were analysed for the three studies that were informed by a systematic review. In the first study, multilevel analysis accounting for some predictors of residential self-selection such as income and marital status was performed to examine the association between six perceived environment characteristics and the odds of developing incident T2DM. Interaction terms were also fitted between the built environment variables and some sociodemographic factors such as area disadvantage and gender. In the second study, the potential role of several hypothesised mediators of the built environment–T2DM association was tested in regression-based causal mediation analysis. The final study examined the potential moderating role of perceived crime on the built environment–T2DM association by fitting interaction terms and stratified models. A moderated mediation analysis tested the possible moderating role of perceived crime on the mediation of the association between perceived local amenities and T2DM incidence.

Results: Of the total participants, 3.7% developed T2DM at follow-up, and the odds of developing incident T2DM varied geographically. The results of the first study showed that lack of access to neighbourhood amenities and day- and night-time crime were associated with higher odds of developing incident T2DM. These associations retained significance even after accounting for the markers of residential self-selection. In the second study, body mass index (BMI) and physical activity including walking partially mediated the association between perceived local amenities and T2DM. Psychological distress and BMI partially mediated the association between both day- and night-time crime and T2DM, while physical activity and walking also partially mediated the association for day crime. The final study showed that regardless of area crime, lack of access to local amenities increased BMI level, which in turn increased the odds of developing T2DM. Similarly, access to local amenities was protective against T2DM among those who perceived their neighbourhood safe in relation to day crime, and recreational walking partially mediated this association. The clustering of the perceived unfavourable built environment was associated with increased odds of T2DM, which rose with increasing unfavourable environment and area disadvantage.

Conclusions: The findings suggest that policies to enhance access to local amenities and prevent crime can potentially reduce T2DM risk by supporting healthy behaviour and improving physical and mental health. The results also imply that the availability of amenities may lower T2DM risk by increasing walking and by reducing BMI regardless of perceived area crime. Environmental interventions that promote health, especially in disadvantaged areas, may return larger gains. Modifying the features of the residential built environment, such as enhancing proximity to local amenities, reducing crime, and addressing mental health, may help control the growing epidemic of T2DM and related health outcomes.

FoR codes (2008)

111706 Epidemiology

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Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.