Neighborhoods, obesity, and diabetes--a randomized social experiment

Abstract

Background: The question of whether neighborhood environment contributes directly to the development of obesity and diabetes remains unresolved. The study reported on here uses data from a social experiment to assess the association of randomly assigned variation in neighborhood conditions with obesity and diabetes.

Methods: From 1994 through 1998, the Department of Housing and Urban Development (HUD) randomly assigned 4498 women with children living in public housing in high-poverty urban census tracts (in which ≥40% of residents had incomes below the federal poverty threshold) to one of three groups: 1788 were assigned to receive housing vouchers, which were redeemable only if they moved to a low-poverty census tract (where <10% of residents were poor), and counseling on moving; 1312 were assigned to receive unrestricted, traditional vouchers, with no special counseling on moving; and 1398 were assigned to a control group that was offered neither of these opportunities. From 2008 through 2010, as part of a long-term follow-up survey, we measured data indicating health outcomes, including height, weight, and level of glycated hemoglobin (HbA(1c)).

Results: As part of our long-term survey, we obtained data on body-mass index (BMI, the weight in kilograms divided by the square of the height in meters) for 84.2% of participants and data on glycated hemoglobin level for 71.3% of participants. Response rates were similar across randomized groups. The prevalences of a BMI of 35 or more, a BMI of 40 or more, and a glycated hemoglobin level of 6.5% or more were lower in the group receiving the low-poverty vouchers than in the control group, with an absolute difference of 4.61 percentage points (95% confidence interval [CI], -8.54 to -0.69), 3.38 percentage points (95% CI, -6.39 to -0.36), and 4.31 percentage points (95% CI, -7.82 to -0.80), respectively. The differences between the group receiving traditional vouchers and the control group were not significant.

Conclusions: The opportunity to move from a neighborhood with a high level of poverty to one with a lower level of poverty was associated with modest but potentially important reductions in the prevalence of extreme obesity and diabetes. The mechanisms underlying these associations remain unclear but warrant further investigation, given their potential to guide the design of community-level interventions intended to improve health. (Funded by HUD and others.).

Figure 1. Screening and Randomization

BMI denotes body-mass index. P1 (the share of the total sample in phase 1) = phase 1 subtotal ÷ (phase 1 + phase 2 subtotals). P2 (the share of the total sample in phase 2) = phase 2 subtotal ÷ (phase 1 + phase 2 subtotals). R1 (the response rate from phase 1) = phase 1 analysis sample ÷ phase 1 subtotal. R2 (the response rate from phase 2) = phase 2 analysis sample ÷ (phase 2 subtotal − phase 2 randomly selected for exclusion). The analysis sample refers to the sample for the BMI analysis or the sample for the glycated hemoglobin analysis. The effective response rate = (P1 × R1) + (P2 × R2).

Figure 2. Census-Tract Poverty Rate According to Study Group and Years since Randomization

The horizontal line in the middle of each vertical bar indicates the median of the census-tract poverty rates within each randomly assigned group, the upper and lower boundaries of each bar mark the 75th and 25th percentiles, and the I bars (whiskers) mark the 90th and 10th percentiles. Census tracts are small geographic areas that usually contain between 2500 and 8000 people and were defined by the Census Bureau to correspond to local communities that have relatively homogeneous population characteristics. The censustract poverty rate for families in the study 1, 5, or 10 years after randomization was linearly interpolated from data in the 1990 and 2000 decennial censuses and the American Community Survey for 2005 through 2009. The sample includes 3026 women for whom there was a valid measure of body-mass index or a valid measure of the glycated hemoglobin level in addition to valid addresses at baseline and at the three time points shown.