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.