50-year trends in US socioeconomic inequalities in health: US-born Black and White Americans, 1959-2008

Background: Debates exist over whether health inequities are bound to rise as population health improves, due to health improving more quickly among the better off, with most analyses focused on mortality data. Methods: We analysed 50 years of socioeconomic inequities in measured health status among US-born Black and White Americans, using data from the National Health Examination Surveys (NHES) I-III (1959-70), National Health and Nutrition Examination Surveys (NHANES) I-III (1971-94) and NHANES 1999-2008. Results: Absolute US socioeconomic health inequities for income percentile and education variously decreased (serum cholesterol; childhood height), stagnated [systolic blood pressure (SBP)], widened [body mass index (BMI), waist circumference (WC)] and in some cases reversed (age at menarche), even as on-average values rose (BMI, WC), idled (childhood height) and fell (SBP, serum cholesterol, age at menarche), with patterns often varying by race/ethnicity and socioeconomic measure; similar results occurred for relative inequities. For example, for WC, the adverse 20th (low) vs 80th (high) income percentile gap increased only among Whites (NHES I: 0.71cm [95% confidence interval (CI) -0.74, 2.16); NHANES 2005-08: 2.10 (95% CI 0.96, 3.62)]. By contrast, age at menarche for girls in the 20th vs 80th income percentile among Black girls remained consistently lower, by 0.34 years (95% CI 0.12, 0.55) whereas among White girls the initial null difference became inverse [NHANES 2005-08: -0.49 years (95% CI -0.86, -0.12; overall P = 0.0015)]. Adjusting for socioeconomic position only modestly altered Black/White health inequities. Conclusions: Health inequities need not rise as population health improves.