Association of Body Mass Index With All-Cause Mortality in Acutely Hospitalized Older Patients

OBJECTIVES: The aim was to examine the relationship between body mass index (BMI) and mortality in older hospitalized patients taking activities of daily living (ADLs) into account.

DESIGN: Retrospective cohort study.

SETTING AND PARTICIPANTS: Nationwide population-based study of all patients aged ≥65 years admitted to Danish geriatric medical departments during 2005 to 2014 and included in the National Danish Geriatric Database.

METHODS: Patients were followed until death, emigration, or study termination (December 31, 2015). Primary outcome was all-cause mortality. BMI and ADLs were routinely assessed on admission and linked at an individual level to the Danish national health registers. Kaplan-Meier analysis was used to estimate crude survival according to each BMI subcategory and Cox regression to examine the association with mortality adjusting for age, comorbidity, polypharmacy, ADLs, marital status, prior hospitalizations, and admission year.

RESULTS: In total, 74,589 patients (63% women) were included aged [mean (SD)] 82.5 (7.5) years with BMI [mean (SD)] of 23.9 (5.1) kg/m2. During follow-up 51,188 died. Follow-up time was 191,972 person-years. Unadjusted and adjusted hazard ratio (HR) for overall, 30-day, and 1-year mortality decreased significantly with increasing BMI. In women, the highest adjusted HR (95% confidence interval) for overall mortality was seen for underweight patients (BMI <16) 1.83 (1.72-1.95) and the lowest for obesity grade II patients (BMI = 35.0-39.9) 0.66 (0.60-0.73) when using normal weight (BMI = 18.5-24.9) as reference. In men, the HR for BMI <16 and BMI = 35.0-39.9 were 1.98 (1.76-2.23) and 0.56 (0.49-0.65), respectively.

CONCLUSIONS AND IMPLICATIONS: In hospitalized older patients, association between mortality and BMI did not show a U-shaped or J-shaped curve after adjustment of multiple confounders, including ADLs. Instead, mortality was highest in patients with low BMI and decreased with increasing BMI before leveling off in the obese range. Our study highlights the need for a debate and reassessment of what should be the ideal BMI in this vulnerable patient group.