Neighborhood walkability and pre-diabetes incidence in a multiethnic population

Introduction

The current wave of type 2 diabetes is a global public health concern. Rapid rises in obesity in many areas of the world combined with an aging population have contributed to an increase in the prevalence of type 2 diabetes.1 2 These changes have been particularly marked in low-income and middle-income countries where rapid urbanization and economic development have led to widespread changes in physical activity and diet.3 These trends create a challenge for health systems worldwide and carry substantial economic implications. Projections suggest that diabetes will cost USD $1.7 trillion to world economies between 2011 and 2030 through losses in GDP.4 Policies to address factors within the environment that perpetuate sedentary behaviors and unhealthy eating may help offset the burden and costs associated with diabetes.

Diabetes prevention trials have shown that intensive lifestyle interventions consisting of dietary changes and physical activity were highly effective in reducing the likelihood of transitioning from pre-diabetes to type 2 diabetes.5 These interventions generally involved one-on-one counseling by a team of experts and thus, were associated with considerable costs and resources.6 There are growing concerns regarding the feasibility of broadly incorporating such interventions in real-world clinical settings. In light of this, many governments are searching for effective policies to promote physical activity and healthy eating in the general population.

A growing body of evidence suggests that residents living in older, more compact neighborhoods engage in more physical activity than those living in sprawling, car-dependent areas.7 8 In the International Physical activity and Environment Network study, conducted in 14 cities across Europe and the USA, residents living in activity-friendly neighborhoods were more likely to meet the recommended number of minutes of moderate to vigorous physical activity.7 Countries where a larger proportion of the population walk have a lower prevalence of obesity.8 Moreover, highly walkable neighborhoods have been associated with lower rates of diabetes and other metabolic diseases, presumably through beneficial effects on obesity, weight gain, and insulin resistance.9–14

Pre-diabetes, characterized by mild elevations in glycemia, represents a phase in the course of type 2 diabetes development where prevention strategies _targeting physical activity and diet may be most impactful. It is unknown whether neighborhood environments that support walking can ameliorate these early glucose abnormalities. Also, prior studies have not examined the consistency of these associations across higher and lower risk populations. The primary objective of this study was to examine whether neighborhood walkability is a risk factor for pre-diabetes development in general, and among ethnic groups with varying levels of risk for type 2 diabetes. Further, we sought to examine whether neighborhood walkability modifies the effects of ethnicity on pre-diabetes incidence.We hypothesized that highly walkable neighborhoods would be associated with a reduced incidence of pre-diabetes relative to less walkable areas and that differences between ethnic groups would vary more in low walkability settings than highly walkable ones.

Methods

Results

Overall, our study population consisted of 267 529 and 860 652 immigrants and long-term residents, respectively. Baseline characteristics of the study population according to most and least neighborhood walkability and by ethnicity are shown in tables 1 and 2, and online supplementary table 2, respectively. A greater proportion of the most walkable neighborhoods were low income (table 1). Across all ethnic groups, a significant proportion of immigrants had high school education or less and more than half reported English proficiency at the time of application for immigration (table 2). The largest proportion of immigrants in our sample were from South Asia and East Asia. A relatively higher proportion of immigrants lived in less walkable neighborhoods, particularly those of South Asian, West Asian and Arab, and Eastern Europeans compared with other ethnic groups. There were few differences in the prevalence of underlying metabolic abnormalities at baseline (ie, previous hypertension, low HDL, high triglycerides, and total cholesterol) between people living in least and most neighborhood walkability decile, and across different ethnic groups (tables 1 and 2 and online supplementary table 2).

Over a median follow-up of 8.4 years, 50 971 immigrants developed pre-diabetes, of whom 5641 lived in neighborhoods in the lowest walkability decile (crude incidence rate of 3.48 per 100 person-years), and 4407 lived in neighborhoods in the most walkable decile (crude incidence rate of 3.30 per 100 person-years). Living in the least (D1) versus most (D10) walkable neighborhood was associated with a significantly increased risk of developing pre-diabetes overall (adjusted HR 1.17, 95% CI 1.15 to 1.19), as well as among immigrants (adjusted HR 1.20, 95% CI 1.15 to 1.25) and long-term residents (adjusted HR 1.15, 95% CI 1.13 to 1.18) (figure 1). Furthermore, there was a significant interaction between area walkability and ethnicity (p<0.0001 for the interaction), suggesting that low walkability was an important risk factor for some but not all ethnic groups (figure 2). For example, living in the least walkability neighborhood was associated with a 17% to 32% higher incidence of pre-diabetes relative to those living in high walkability areas among immigrants from West Asia and Arab, Latin Americans, Sub-Saharan African and the Caribbean, and Southeast Asian populations. However, low walkability had a neutral (South Asians and East Asians) or reverse association (Western Europeans) among other groups.

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Overall, ethnicity was an important predictor of pre-diabetes incidence with many non-European immigrant groups having a higher risk of developing pre-diabetes than immigrants of European descent (figure 3). However, ethnic disparities were more marked in the least walkability neighborhoods and substantially diminished in the most walkability areas, depending on the population. For example, among immigrants living in low walkability areas, South Asians (HR 2.40, 95% CI 2.08 to 2.76) and Sub-Saharan African and Caribbeans (HR 2.11, 95% CI 1.81 to 2.46) had twice the incidence of pre-diabetes relative to Western Europeans after adjusting for sociodemographic and immigration factors (figure 3). These same groups had only a 10% (HR 2.10, 95% CI 1.83 to 2.41) and 24% higher (HR 1.24, 95% CI 1.08 to 1.42) incidence relative to Western Europeans in high walkability areas, respectively. West Asians and Arabs, Latin Americans, and East Asians had a 33%–50% higher risk of developing pre-diabetes relative to Western Europeans in low walkability areas but nearly identical incidence rates to this group in more walkable neighborhoods. Although in the least walkability areas, South Asian populations had the highest incidence of pre-diabetes at more than twice the incidence of Western Europeans, the association with neighborhood walkability changed the least when comparing the most to least walkable deciles. Lastly, our analyses based on the ADA/EASD cut-offs for pre-diabetes yielded similar results, as shown in online supplementary tables 3–5.

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Discussion

In this study, residents living in highly walkable neighborhoods had a lower likelihood of developing pre-diabetes than those living in less walkable areas. Individuals of non-European descent developed pre-diabetes at a more accelerated rate than Western Europeans, with some ethnic groups including South Asians and Sub-Saharan Africans and Caribbeans demonstrating a twofold increase in pre-diabetes incidence. However, this disparity was primarily observed among those living in low walkability areas–and was markedly diminished among those living in high walkability areas. These findings support the notion that neighborhood designs that encourage walking and other physical activities could potentially help to reduce the burden of diabetes in certain populations by preventing earliest stages of diabetes development.

Growing evidence has shown that people living in more walkable neighborhoods have higher overall levels of physical activity and as a result are more likely to meet recommended guidelines for the number of minutes of moderate to vigorous physical activity per week.7 These associations may contribute to the reduced prevalence of obesity and lower incidence of diabetes observed among those living in high walkability neighborhoods.8–14 Findings from our study revealed that the benefits of walkability may extend to the earliest stages of type 2 diabetes development—prior to even the mildest elevation in glucose. Concordant with our findings, a small, randomized controlled trial from the UK showed that a strategy that promoted physical activity through walking was effective in improving glucose tolerance and fasting glucose levels.20 Findings from the Multiethnic Study of Atherosclerosis cohort in the USA found that residents who reported greater access to physical activity resources and healthy foods were less likely to develop insulin resistance and type 2 diabetes.21 Thus, neighborhood designs that support residents in making positive behavioral changes, including the ability to walk or perform other physical activities on a regular basis, may help to reduce the community-level burden of pre-diabetes or type 2 diabetes.

One of the most important features of walkable neighborhoods is that they provide opportunities to engage in various forms of physical activity.22 In recent decades, urban planning practices have shifted toward sprawling urban developments with separation of lands for residential and commercial purposes.9 Such designs may limit opportunities for walking or cycling as a means of transportation or to conduct errands, as opposed to neighborhoods built prior to World War II that are more compact and offer greater access to retail destinations within walking distance of residents’ homes.9 As a result, increasing reliance on vehicles for transportation is thought to have contributed to reduced levels of physical activity and more time spent on other sedentary forms of transportation.10 In our study, the majority of immigrants lived in sprawling, car-dependent neighborhoods which offer fewer opportunities for physical activity, thereby contributing in theory to an increased risk of pre-diabetes development.

In this study, the associations between walkability and pre-diabetes incidence varied across ethnic groups for reasons that were unclear. This may be due to differences in the propensity for different ethnic populations to walk within residential areas, which may vary depending on cultural attitudes toward walking and/or a preference toward other physical activities. Studies from the USA, UK, and Canada have shown that non-whites and South Asians in particular were less physically active compared with people of other ethnicities.23–25 In addition, the type of physical activity varies by ethnicity; for example, some ethnic groups participate in recreational activities, while others prefer organized exercise programs or home-based exercises.26 Hence, neighborhood-level walkability measures may not be an ideal proxy for overall physical activity behaviors in certain ethnic groups. Furthermore, other neighborhood factors such as perceptions of safety (eg, levels of crime, sidewalk repairs, and lighting), seasonality, access to healthy versus unhealthy food options, social cohesion, and enhanced social support in ethnic enclaves may also influence the extent to which people walk within their neighborhood, along with other risk factors for diabetes.27–29 Hence, neighborhoods that support healthy living may be necessary, but perhaps not sufficient to enable all residents to be healthy and active.

This study has several limitations. First, administrative and immigration databases were used to classify individuals into appropriate ethnic origins, and due to heterogeneity in ethnic identities, some misclassification may have occurred. Second, self-selection may lead to confounding if residents who choose to live in high versus low walkability neighborhoods based on non–health-related factors (ie, proximity to work or school, affordability, etc) or prefer to do so are inherently healthier. However, studies that have attempted to address self-selection bias have found significant associations between walkability, physical activity, and diabetes risk.30 Furthermore, we assumed that people remained in the same neighborhood during the follow-up period due to missing data on changes in address. Third, our study also lacked information on behavioral data such as body mass index, physical activity level, or diet. Other Canadian studies suggest that overweight and obesity rates remained lower over time in highly walkable areas, and those living in highly walkable areas or moving from areas of low to high walkability gain less weight over time.11–13 However, the baseline metabolic profile of our study population by immigration status and ethnicity were comparable for those living in the least and most neighborhood walkability decile. Fourth, the long-term resident group may have included individuals who arrived to Canada prior to 1985, leading to some degree of misclassification. Also, because the IRCC-PR data include sociodemographic information on immigrants only, ethnicity could not be derived for long-term residents. Fifth, we did not account for differences in the retail food environment across neighborhoods which may have offset potential benefits of highly walkable neighborhoods.27 Sixth, in this study we did not examine the impact of air pollution concentrations as a contributing risk factor for pre-diabetes development. However, other studies have shown that concentrations of traffic-related air pollutants, such as nitric oxide, may be higher in some highly walkable areas due to idling of cars—a factor that might offset the benefits of high walkability on diabetes risk.31 32 Lastly, although we did not examine healthcare utilization via primary care visits, prior research suggests that under Ontario’s universal healthcare plan, screening rates for diabetes are high among immigrant populations.33

Pre-diabetes is a critical window for diabetes prevention and a risk factor for other chronic diseases including cardiovascular disease and certain cancers.34 Our study was the first to examine the effect of walkability on early markers of dysglycemia in populations at high risk of developing diabetes and to investigate the extent to which the susceptibility to walkability varied across ethnic groups. Our findings suggest that urban environments that support physical activity may help to reduce the development of pre-diabetes. However, while these findings may appear intuitive, randomized trials in this field are not feasible; thus, it is not known whether policies that increase neighborhood walkability would in fact translate into fewer cases of diabetes. The growing enthusiasm among city planners to adopt healthy urban designs provides an opportunity for researchers to study the effects of such natural experiments on diabetes and related diseases. From our research, built environment interventions alone are unlikely to be effective in all populations. This is because a one-size-fits-all solution is unlikely to be sufficient when considering interventions to reach all populations. Further research is needed to understand the causes for the ethnic disparities we observed, including the factors influencing whether people walk in their neighborhoods. Our findings also suggest that the effects of ethnicity differ depending on the context in which people live. Therefore, future research should strive to understand the contextual factors contributing to diabetes risk in high-risk populations to inform built environment policies and more _targeted interventions to promote healthier lifestyles in high-risk populations. Urban design interventions could adopt more equitable strategies for building neighborhoods that are livable, walkable, and sustainable which _target populations at greatest risk for chronic diseases. Achieving this aim requires collaborations across multiple sectors and levels of government and a greater understanding of the barriers and promotors influencing the adoption of healthy behaviors in high-risk communities.35