The Contribution of Differences in Adiposity to Educational Disparities in Mortality in the United States

Background: There are large differences in life expectancy by educational attainment in the United States. Previous research has found obesity’s contribution to these differences to be small. Those findings may be sensitive to how obesity is estimated. Methods: This analysis uses discrete time logistic regressions with data from the National Health and Nutrition Examination Survey (NHANES), pooled from 1988-1994 and 1999-2010, to estimate the contribution of differences in adiposity, or body fat, to educational differences in mortality. I show that results depend upon the measure of adiposity used: body mass index (BMI) at survey or lifetime maximum BMI. Results: High school graduates had higher BMIs at time of survey than college graduates (28.6 vs 27.3, respectively), as well as higher maximum BMIs (30.8 vs 29.1, respectively. Lifetime maximum BMI performed better than BMI at survey time in predicting mortality using criteria for model selection. Differences in maximum BMI were associated with 9.2% of educational mortality differences, compared to 2.2% for BMI at survey. Among non-smokers, 15.8% of the differential was associated with differences in maximum BMI. Contribution: Adiposity is an overlooked contributor to educational differences in mortality. Previous findings that obesity does not contribute to educational disparities were based on BMI at survey, which is less informative than maximum BMI. The contribution of adiposity to educational mortality differences will likely grow as smoking prevalence declines. Health surveys should collect information on weight history.