Environmental Risk Factors for Developing Type 2 Diabetes Mellitus: A Systematic Review

Abstract

Different elements of the environment have been posited to influence type 2 diabetes mellitus (T2DM). This systematic review summarizes evidence on the environmental determinants of T2DM identified in four databases. It proposes a theoretical framework illustrating the link between environment and T2DM, and briefly discusses some methodological challenges and potential solutions, and opportunities for future research. Walkability, air pollution, food and physical activity environment and roadways proximity were the most common environmental characteristics studied. Of the more than 200 reported and extracted relationships assessed in 60 studies, 82 showed significant association in the expected direction. In general, higher levels of walkability and green space were associated with lower T2DM risk, while increased levels of noise and air pollution were associated with greater risk. Current evidence is limited in terms of volume and study quality prohibiting causal inferences. However, the evidence suggests that environmental characteristics may influence T2DM prevention, and also provides a reasonable basis for further investigation with better quality data and longitudinal studies with policy-relevant environmental measures. This pursuit of better evidence is critical to support health-orientated urban design and city planning.

Keywords: air pollution; environment; green space; noise; type 2 diabetes mellitus; walkability.

Figure 1

Schematic illustration of possible pathways through which environment impacts type 2 diabetes mellitus (T2DM) risk. Adapted from Poortinga [34], Northridge et al. [41], and Giles-Corti et al. [42]. ^I include walking, jogging and cycling infrastructure, open spaces, trails, etc.; ^II include supermarkets, shops, food outlets, recreational and other facilities, etc.; ^III include street connectivity, density, land use, sidewalks, walkable destinations, etc.; ^IV include housing condition, design, aesthetics, etc.; ^V smoking and drinking; ^VI high blood sugar levels below the range of T2DM diagnosis, also referred to as impaired glucose tolerance (IGT) or impaired fasting glucose (IFG).

Figure 2

Flow chart illustrating the search and selection process.

Figure 3

Number of studies and environmental characteristics studied by year. Physical includes roadways proximity, walkability, open space, green space, tree canopy, traffic, noise, urban sprawling, and slope; Amenities includes food and physical activity environment, recreational facilities, transport system, and health service; Social includes safety, violence, crime, physical disorder, area and housing conditions, and infrastructure.