Obesity and US mortality risk over the adult life course

Abstract

In this study, we analyzed age variation in the association between obesity status and US adult mortality risk. Previous studies have found that the association between obesity and mortality risk weakens with age. We argue that existing results were derived from biased estimates of the obesity-mortality relationship because models failed to account for confounding influences from respondents' ages at survey and/or cohort membership. We employed a series of Cox regression models in data from 19 cross-sectional, nationally representative waves of the US National Health Interview Survey (1986-2004), linked to the National Death Index through 2006, to examine age patterns in the obesity-mortality association between ages 25 and 100 years. Findings suggest that survey-based estimates of age patterns in the obesity-mortality relationship are significantly confounded by disparate cohort mortality and age-related survey selection bias. When these factors are accounted for in Cox survival models, the obesity-mortality relationship is estimated to grow stronger with age.

Figure 1.

Estimated mortality hazard ratios from models 1 (proportional) and 2 (grouped age coefficients) for obese persons (body mass index (BMI; weight (kg)/height (m)²) ≥30.0) versus normal-weight and overweight persons (BMI 18.5–29.9) in the United States, by sex, 1986–2006. Data were obtained from the National Health Interview Survey Linked Mortality Files. Models 1 and 2 were adjusted for educational attainment, income, marital status, and region of residence. The estimated proportional hazard ratio from model 1 is indicated by a gray line; the estimated age-specific hazard ratio from model 2 is indicated by black bars. Men's results are shown in column 1, women's results in column 2. Grade 1 obesity (BMI 30.0–34.9) is shown in row 1, grade 2 obesity (BMI 35.0–39.9) in row 2, and grade 3 obesity (BMI ≥40.0) in row 3.

Figure 2.

Estimated mortality hazard ratios from model 3 for obese persons (body mass index (BMI; weight (kg)/height (m)²) ≥30.0) versus normal-weight and overweight persons (BMI 18.5–29.9) in the United States, by sex, 1986–2006. Data were obtained from the National Health Interview Survey Linked Mortality Files. Model 3 was adjusted for educational attainment, income, marital status, region of residence, birth cohort, age at survey, and the 2-way interaction between obesity status and age at survey. The estimated age-specific hazard ratio is indicated by black bars, and 95% confidence intervals are indicated by dashed lines. Men's results are shown in column 1, women's results in column 2. Grade 1 obesity (BMI 30.0–34.9) is shown in row 1, grade 2 obesity (BMI 35.0–39.9) in row 2, and grade 3 obesity (BMI ≥40.0) in row 3.