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

Abstract

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.

Figure 1. Percent immigrants by municipality in the year before and after the study period

Note: Data from Statistics Sweden. Municipalities were classified into quintiles at baseline in order to create categories. The policy was strictly enforced during 1987–1991.

Figure 2. Number of new refugees in Sweden by year, 1951–2014

Note: Data from the United Nations High Commissioner for Refugees (UNHCR) Population Statistics Database, available online at http://popstats.unhcr.org and accessed on October 10, 2015. The counts include refugees, asylum seekers, internally displaced persons, and stateless persons.

Figure 3. Odds ratios of diabetes risk by deprivation level

Note: N = 61,386. Odds ratios are derived from logistic regression models. The adjusted model includes 5-year age categories, sex, educational attainment, marital status, region of initial placement, family size, region of origin, and year of arrival. Parentheses indicate 95% confidence intervals, with robust standard errors clustered by municipality.

Figure 4. Cumulative effect of neighborhood deprivation on diabetes risk over time

Note: N = 61,386. This figure plots the marginal effects of neighborhood deprivation relative to low-deprivation areas, derived from separate yearly regression models corresponding to Model 2 in Table 3. The dotted line indicates the point at which the prescription drug register became available for identifying diabetes cases.