Neighbourhood socioeconomic status and biological 'wear and tear' in a nationally representative sample of US adults.

OBJECTIVE: To assess whether neighbourhood socioeconomic status (NSES) is independently associated with disparities in biological 'wear and tear' measured by allostatic load in a nationally representative sample of US adults.
DESIGN: Cross-sectional study.
SETTING: Population-based US survey, the Third National Health and Nutrition Examination Survey (NHANES III), merged with US census data describing respondents' neighbourhoods. PARTICIPANTS: 13,184 adults from 83 counties and 1805 census tracts who completed NHANES III interviews and medical examinations and whose residential addresses could be reliably geocoded to census tracts. MAIN OUTCOME MEASURES: A summary measure of biological risk, incorporating nine biomarkers that together represent allostatic load across metabolic, cardiovascular and inflammatory subindices.
RESULTS: Being male, older, having lower income, less education, being Mexican-American and being both black and female were all independently associated with a worse allostatic load. After adjusting for these characteristics, living in a lower NSES was associated with a worse allostatic load (coefficient -0.46; CI -0.079 to -0.012). The relationship between NSES and allostatic load did not vary significantly by gender or race/ethnicity.
CONCLUSIONS: Living in a lower NSES in the USA is associated with significantly greater biological wear and tear as measured by the allostatic load, and this relationship is independent of individual SES characteristics. Our findings show that where one lives is independently associated with allostatic load, thereby suggesting that policies that improve NSES may also yield health returns.