Poverty or income inequality as predictor of mortality: longitudinal cohort study

Abstract

Objective: To determine the effect of inequality in income between communities independent of household income on individual all cause mortality in the United States. Design: Longitudinal cohort study. Subjects: A nationally representative sample of 14 407 people aged 25-74 years in the United States from the first national health and nutrition examination survey. Setting: Subjects were followed from initial interview in 1971-5 until 1987. Complete follow up information was available for 92.2% of the sample. Main outcome measures: Relation between both household income and income inequality in community of residence and individual all cause mortality at follow up was examined with Cox proportional hazards survival analysis. Results: Community income inequality showed a significant association with subsequent community mortality, and with individual mortality after adjustment for age, sex, and mean income in the community of residence. After adjustment for individual household income, however, the association with mortality was lost. Conclusions: In this nationally representative American sample, family income, but not community income inequality, independently predicts mortality. Previously reported ecological associations between income inequality and mortality may reflect confounding between individual family income and mortality. Key messages: Ecological studies have documented a powerful relation between national, state, or community indices of inequality and mortality at the population level These studies have not adequately controlled for confounding by family income measured at the individual level This study, using data from a nationally representative sample from the United States, showed no relation between community income inequality and mortality after adjustment for family income Poverty, not community income inequality, determines subsequent mortality; further study is needed to determine whether these findings apply to national or state-wide income inequality