Articles
Long-term effects of neighbourhood deprivation on diabetes risk: quasi-experimental evidence from a refugee dispersal policy in Sweden

https://doi.org/10.1016/S2213-8587(16)30009-2Get rights and content

Summary

Background

Although studies have shown associations between neighbourhood quality and chronic disease outcomes, such associations are potentially confounded by the selection of different types of people into different neighbourhood environments. We sought to identify the causal effects of neighbourhood deprivation on type 2 diabetes risk, by comparing refugees in Sweden who were actively dispersed by government policy to low-deprivation, moderate-deprivation, or high-deprivation neighbourhoods.

Methods

In this quasi-experimental study, we analysed national register data for refugees who arrived in Sweden aged 25–50 years, at a time when the government policy involved quasi-random dispersal of refugees to neighbourhoods with different levels of poverty and unemployment, schooling, and social welfare participation. Individuals in our sample were assigned to a neighbourhood categorised as high deprivation (≥1 SD above the mean), moderate deprivation (within 1 SD of the mean), or low deprivation (≥1 SD below the mean). The primary outcome was new diagnosis of type 2 diabetes between Jan 1, 2002, and Dec 31, 2010. We used multivariate logistic and linear regressions to assess the effects of neighbourhood deprivation on diabetes risk, controlling for potential confounders affecting neighbourhood assignment and assessing effects of cumulative exposure to different neighbourhood conditions.

Findings

We included data for 61 386 refugees who arrived in Sweden during 1987–91 and who were assigned to one of 4833 neighbourhoods. Being assigned to an area deemed high deprivation versus low deprivation was associated with an increased risk of diabetes (odds ratio [OR] 1·22, 95% CI 1·07–1·38; p=0·001). In analyses that included fixed effects for assigned municipality, the increased diabetes risk was estimated to be 0·85 percentage points (95% CI −0·030 to 1·728; p=0·058). Neighbourhood effects grew over time such that 5 years of additional exposure to high-deprivation versus low-deprivation neighbourhoods was associated with a 9% increase in diabetes risk.

Interpretation

This study makes use of a pre-existing governmental natural experiment to show that neighbourhood deprivation increased the risk of diabetes in refugees in Sweden. This finding has heightened importance in the context of the current refugee crisis in Europe.

Funding

US National Heart, Lung, and Blood Institute, US National Center for Advancing Translational Sciences, US National Institute on Minority Health and Health Disparities, Swedish Research Council.

Introduction

Studies have shown that adverse neighbourhood socioeconomic characteristics are associated with worse chronic disease outcomes.1 Of note, findings of several studies have shown a strong association between disadvantaged neighbourhood environments and the incidence of insulin resistance and type 2 diabetes.2, 3, 4 Potential mediating pathways include reduced employment and income opportunities resulting in the purchase of cheap, unhealthy food; reduced psychosocial resources resulting in high chronic stress; and poor food availability and walkability.5 Unfortunately, most studies of neighbourhoods and health have shown correlations and were unable to account for several methodological limitations such as selection bias (eg, less healthy individuals might move to more disadvantaged neighbourhoods), confounding by unobserved individual factors (eg, family socioeconomic status), and an inability to separate individual-level and area-level factors.6, 7, 8 The only randomised trial done so far is the Moving to Opportunity experiment,9 in which individuals in five US cities were randomly assigned to a group offered a housing voucher that could only be used to move to a low-poverty neighbourhood, a group offered a traditional Section 8 housing voucher, or a control group. Investigators noted a small but statistically significant reduction in the prevalence of obesity and type 2 diabetes in the group who received a housing voucher to move to a low-poverty neighbourhood.9 Moving to Opportunity has been criticised on methodological grounds, such as residual selection bias and limited generalisability.10, 11

In this study, we overcome persistent challenges in the scientific literature on neighbourhood effects by means of a novel quasi-experiment. We took advantage of a policy in Sweden during 1985–94 that assigned incoming refugees in a quasi-random fashion to neighbourhoods throughout the country. The policy's goal was to ease labour market conditions in heavily settled areas and promote better integration of refugees. The dispersal policy was most strictly applied from 1987–91,12 creating a unique study group that enabled investigation of how neighbourhood environment affects the onset of type 2 diabetes. As a result of the dispersal policy, refugees were spread more evenly across the country during this period than before its implementation (figure 1). Several studies have assessed the effect of European refugee dispersal policies on labour markets, crime, and educational outcomes.12, 13, 14 Only one has assessed health outcomes, and found that neighbourhood income inequality was not associated with risk of being admitted to hospital.15 A significant contribution of the present study is the follow-up of more than 20 years, longer than existing experimental or quasi-experimental studies of neighbourhoods and health.

Research in context

Evidence before this study

We searched PubMed for studies of neighbourhood characteristics and type 2 diabetes with the following search terms: “diabetes” and “neighborhoods” or “neighbourhoods.” We restricted our search to articles published in English before Nov 31, 2015. We identified more than 12 observational studies that investigated the association between neighbourhood characteristics and the prevalence or incidence of type 2 diabetes. Most findings showed an association between increased diabetes risk and various measures of neighbourhood deprivation. However, we found only one randomised trial, the Moving to Opportunity experiment. In this trial, investigators noted that women whose family received a voucher to relocate to a low-deprivation neighbourhood had a 4 percentage point reduction in their likelihood of having an HbA1c concentration of 6·5% or higher at 10–15 years of follow-up. We did not find any quasi-experimental evidence on this topic. In our search of the broader scientific literature on neighbourhood health effects, we found no other randomised trials and one quasi-experimental study, which noted no association between neighbourhood-level income inequality and risk of being admitted to hospital for any cause.

Added value of this study

In this study, we took advantage of a unique quasi-experimental policy to assess the causal association between neighbourhood deprivation and type 2 diabetes risk. To our knowledge, this is the first quasi-experiment including neighbourhood deprivation and any health outcome, building on existing correlational and experimental evidence. Our follow-up of more than 20 years is longer than the Moving to Opportunity experiment and most observational studies of neighbourhoods and type 2 diabetes. Our results suggest that exposure to neighbourhood deprivation increased diabetes risk in our sample.

Implications of all the available evidence

Combined with existing evidence, our data suggest that the association between neighbourhood deprivation and type 2 diabetes risk is not driven solely by selection of families into neighbourhoods or other confounding factors. Neighbourhood environments have a causal effect on diabetes risk, which accumulates over time. Policy efforts to reduce area-level socioeconomic disparities might contribute to lowering the risk of type 2 diabetes. The focus of our study is the effects of neighbourhoods on refugees who arrived in Sweden 25–30 years ago. Although policy makers should be cautious about generalisability, these findings nevertheless have important implications for the unprecedented current movement of refugees and migrants to Europe.

Neighbourhood effects are especially important for vulnerable populations, such as immigrants. Studies have consistently shown that immigrants to Sweden, as elsewhere, have an increased risk of diabetes and mortality compared with the native population, and higher incident diabetes after migration from a lower-income country.3, 16, 17 Moreover, incidence might be higher in refugees than in immigrants more generally.18 In the past 2 years, the European Union has experienced the largest inflow of asylum seekers since the end of World War 2.19 The current period of immigration includes mostly individuals from the Middle East and north Africa, where prevalence of type 2 diabetes is the highest of any region worldwide: 11% in adults aged 20–79 years in 2013.20 Although policy makers have focused on the economic, political, and cultural implications of integrating many immigrants into a country, mass migration also has ramifications for the health and welfare of the newly settled immigrants. Therefore, we aimed to test the hypothesis that neighbourhood deprivation affects the development of type 2 diabetes in order to gain crucial insight that could guide the design of community-level interventions to affect the long-term health of refugees in Europe.

Section snippets

Data sources

We drew on data from several national registers on the entire Swedish population, including immigrants (table 1). We linked the datasets by use of personal identification numbers assigned to all permanent residents in Sweden. Individual-level sociodemographic characteristics and aggregated statistics representing the neighbourhood-level variables were available in the total population register. Health outcome data, including the date of each health-care encounter, were available in the

Results

In this quasi-experiment, 61 386 individuals met the selection criteria (figure 3). Table 2 shows the characteristics of the sample at the time of arrival in Sweden. Many refugees in the sample were initially assigned to deprived neighbourhoods (45% to a moderate-deprivation area and 47% to a high-deprivation area), which shows that housing was most readily available in more deprived areas during the arrival period. About two-thirds of the sample was younger than 35 years. About three-quarters

Discussion

Our findings show that refugees initially assigned to highly deprived neighbourhoods had a 1·7 percentage point increased risk of developing type 2 diabetes. Covariate adjustment attenuated the magnitude of the association to 0·8 percentage points. This represents a relative increase of 15–30%. The accumulation of this effect over time is consistent with hypothesised mediating pathways, such as chronic stress, employment status, income opportunities, and food environment, all of which might

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