Overweight or obese BMI is associated with earlier, but not later survival after common acute illnesses

Abstract

Background: Obesity has been associated with improved short-term mortality following common acute illness, but its relationship with longer-term mortality is unknown.

Methods: Observational study of U.S. Health and Retirement Study (HRS) participants with federal health insurance (fee-for-service Medicare) coverage, hospitalized with congestive heart failure (N = 4287), pneumonia (N = 4182), or acute myocardial infarction (N = 2001), 1996-2012. Using cox proportional hazards models, we examined the association between overweight or obese BMI (BMI ≥ 25.0 kg/m²) and mortality to 5 years after hospital admission, adjusted for potential confounders measured at the same time as BMI, including age, race, sex, education, partnership status, income, wealth, and smoking status. Body mass index (BMI) was calculated from self-reported height and weight collected at the HRS survey prior to hospitalization (a median 1.1 year prior to hospitalization). The referent group was patients with a normal BMI (18.5 to < 25.0 kg/m²).

Results: Patients were a median of 79 years old (IQR 71-85 years). The majority of patients were overweight or obese: 60.3% hospitalized for heart failure, 51.5% for pneumonia, and 61.6% for acute myocardial infarction. Overweight or obese BMI was associated with lower mortality at 1 year after hospitalization for congestive heart failure, pneumonia, and acute myocardial infarction-with adjusted hazard ratios of 0.68 (95% CI 0.59-0.79), 0.74 (95% CI: 0.64-0.84), and 0.65 (95%CI: 0.53-0.80), respectively. Among participants who lived to one year, however, subsequent survival was similar between patients with normal versus overweight/obese BMI.

Conclusions: In older Americans, overweight or obese BMI was associated with improved survival following hospitalization for congestive heart failure, pneumonia, and acute myocardial infarction. This association, however, is limited to the shorter-term. Conditional on surviving to one year, we did not observe a survival advantage associated with excess weight.

Keywords: Medicare; acute myocardial infarction; congestive heart failure; hospitalization; obesity; pneumonia.

Fig. 1

Adjusted Hazard (and Odds) Ratios for Mortality in Primary and Sensitivity Analyses Panel a shows 1-year mortality results. Panel b shows 5-year mortality, conditional on survival to one year. The adjusted hazard ratio of overweight or obese BMI, relative to normal BMI (18.5 to < 25.0 kg/m²) is shown. The primary analysis is in white, while sensitivity analyses are shown in color: (1, red) excluding patients with unknown BMI trajectory or declining BMI trajectory prior to hospitalization; (2, orange) adjusting for acute illness severity; (3, yellow) logistic regression model; (4, green) include just one randomly selected hospitalization per person; (5, blue) analysis of age- and sex-matched pairs; and (6, purple) adjustment for pre-morbid disability and select co-morbidities. All models adjust for age, sex, race, marital status, education, smoking status, admission year, number of hospitalizations, household wealth, and household income. Error bars represent the 95% CI for the hazard (or odds) ratio. A hazard or odds ratio of 1.0 indicates no association. A hazard ratio > 1.0 represents a positive association (overweight or obese BMI is associated with greater mortality), while a hazard ratio < 1.0 represents a negative association (overweight or obese BMI is associated with lower mortality)