Body mass index and all-cause mortality among older adults

Objective: To examine the association between baseline body mass index (BMI, kg/m²) and all-cause mortality in a well-characterized cohort of older persons. Methods: The association between BMI (both as a categorical and continuous variable) and all-cause mortality was investigated using 4,565 Geisinger Rural Aging Study participants with baseline age 74.0 ± 4.7 years (mean ± SD) and BMI 29.5 ± 5.3 kg/m² over a mean of 10.9 ± 3.8 years of follow-up. Results: The relationship between BMI (as a continuous variable) and all-cause mortality was found to be U-shaped (P nonlinearity <0.001). Controlling for age, sex, smoking, alcohol, laboratory values, medications, and comorbidity status, underweight (BMI <18.5 kg/m²) individuals had significantly greater adjusted risk of all-cause mortality than persons of BMI 18.5 to 24.9 kg/m² (reference range). Participants with overweight (BMI 25.0–29.9 kg/m²) and class I obesity (BMI 30.0–34.9 kg/m²) had significantly lower adjusted-risk of all-cause mortality. Those with classes II/III obesity (BMI ≥ 35.0 kg/m²) did not have significantly greater adjusted-risk of all-cause mortality. Findings were consistent using propensity score weights and among never-smokers with 2- and 5-year lag analysis and among those with no identified chronic disease. Conclusions: A U-shaped association was observed between BMI and all-cause mortality with lower risk among older persons with overweight and class I obesity in comparison with those with BMI 18.5 to 24.9 kg/m².