TOPLINE

Among US adults aged 65 years or older, overweight and class I/II obesity were associated with lower mortality risk, particularly in men, but this pattern did not extend to waist circumference (WC). Independent of BMI, high WC was associated with a 24% higher mortality risk in both sexes, and even adults with normal BMI faced a 23%-33% higher risk if their WC was high, suggesting that BMI alone may miss key mortality-related risk.

METHODOLOGY

• BMI's inability to account for fat distribution or age-related lean mass loss limits its utility for assessing mortality risk in older adults, prompting expert consensus that WC be incorporated alongside BMI.
• Researchers analyzed 14 years of data (2011-2024) from a nationally representative survey of Medicare beneficiaries aged 65 or older; 6905 participants (56% women) with at least two recorded BMI and WC measurements were included.
• To reduce reverse causation, participants who died within 1 year of baseline were excluded.
• BMI was grouped into five categories, from underweight to class III obesity, whereas WC was labeled "high" or "low" using standard health thresholds; the five categories of BMI were combined with the sex-specific WC cutoffs to create 10 distinct BMI-WC profiles.
• Statistical models estimated mortality risk associated with time-varying BMI and WC categories over follow-up, after adjusting for several confounding factors.

TAKEAWAY

• Adults with BMI in the overweight range had a lower risk for mortality than those with normal BMI — 46% lower (hazard ratio [HR], 0.54) in men and 27% lower (HR, 0.73) in women; men with class I/II obesity also had a 51% lower risk for mortality (HR, 0.49), though this effect was not statistically significant in women.
• Independent of BMI, a high WC was linked to a 24% higher risk for mortality in both men (HR, 1.24) and women (HR, 1.24); a subsequent analysis showed that the risk for mortality was progressively higher with each 5-inch increment in waist size (P = .001 for men, P < .001 for women).
• Being underweight was associated with substantially higher mortality risk than having a normal BMI — 91% higher in men (HR, 1.91) and 97% higher in women (HR, 1.97).
• Adults with a normal BMI but a high WC still faced a higher risk of death (33% higher in men; 23% higher in women) than those with a normal BMI and a low WC, suggesting that waist size may identify mortality risk not captured by BMI alone.

IN PRACTICE

"A key implication is that BMI category alone may inadequately stratify mortality risk in older adults, particularly when central adiposity is not assessed. Instead, abdominal obesity assessed via WC is a more critical health indicator, as it is a strong indicator of regional adiposity," the authors wrote.

SOURCE

The study was led by Furong Xu, College of Education, University of Rhode Island, Kingston. It was published online in the Journal of the American Geriatrics Society.

LIMITATIONS

BMI was based on self-reported height and weight, which may have led to misclassification. Excluding early deaths reduced but did not eliminate the possibility of reverse causation. Some joint BMI-WC groups — especially underweight with a high WC and class III obesity with a low WC — had small sample sizes, reducing the precision of those estimates.

DISCLOSURES

The study did not report specific funding. The authors reported no relevant conflicts of interest.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.