Waist Size, Not Just Weight, Predicts Mortality Risk in Older Adults

Body mass index (BMI) alone misses high-risk older patients with central obesity, according to a 14-year nationally representative study, supporting calls to add waist circumference (WC) to routine clinical assessments.¹

A new study published in the Journal of the American Geriatrics Society reinforces what many clinicians have long suspected: BMI tells an incomplete story when it comes to survival risk in older adults. Among nearly 7000 Medicare beneficiaries followed over 14 years, researchers found that while higher BMI was paradoxically associated with lower mortality, elevated WC independently predicted a 24% greater risk of death—regardless of what the scale suggested.

Researchers at the University of Rhode Island and the University of Connecticut drew on data from the National Health and Aging Trends Study, a nationally representative annual survey of Medicare beneficiaries. The analytic cohort included 6905 participants tracked from 2011 through 2024. Unlike many prior analyses, the study used time-varying BMI and WC, updated at each annual assessment, to more accurately capture real-world changes in body composition over time. Cox proportional hazards models estimated mortality risk by BMI category and WC classification, adjusting for age, race, education, income, smoking status, and homebound status.

The Obesity Paradox

The study confirmed the so-called "obesity paradox" in older adults: compared with those at normal weight, men who were overweight had a 46% lower risk of death (HR, 0.54; 95% CI, 0.45–0.66), and men with class I and II obesity had a 51% lower risk (HR, 0.49; 95% CI, 0.37–0.65). Women who were overweight showed a 27% lower mortality risk. Being underweight, by contrast, carried approximately twice the mortality risk in both sexes.

The apparent protection of higher BMI came with a critical caveat. High WC—greater than 40 inches in men and 35 inches in women—was associated with a 24% greater risk of death in both sexes, independent of BMI. In exploratory analyses, every 5-inch increase in WC corresponded with a significant step-up in mortality risk. Among men, the highest WC category (65 inches or more) carried more than 6 times the mortality risk compared with those under 39.9 inches.

Most strikingly, older adults with normal BMI but high WC faced significantly elevated mortality compared with peers who had normal BMI and low WC (HR, 1.33 in men; HR, 1.23 in women)—a high-risk phenotype that would appear entirely healthy by BMI standards alone.

"A key implication is that BMI category alone may inadequately stratify mortality risk in older adults, particularly when central adiposity is not assessed," the authors wrote.

A Long-Running Debate

The tension between BMI and more nuanced adiposity measures has persisted for years. A 2017 study similarly challenged the obesity paradox by tracking time-varying BMI across 225,072 participants over 16 years.² That analysis found that higher BMI levels of 30 kg/m² or above were linked to increased all-cause mortality once longitudinal weight trajectory was accounted for, suggesting the apparent protective effect of higher weight may reflect methodological limitations rather than a biological reality. Both bodies of evidence point to the same conclusion: single-point assessments are insufficient for capturing the true relationship between adiposity and survival.^1,2

The current findings align with 2025 guidance from the Lancet Commission on Clinical Obesity, which recommended confirming excess adiposity with at least one additional metric, such as WC, waist-to-hip ratio, or direct body fat measurement, rather than relying on BMI alone.¹

References

1. Xu F, Earp JE, Blissmer BJ, Coiro J, Cohen SA, Greene GW. Time-varying body mass index, waist circumference and all-cause mortality in US adults aged 65 or older. J Am Geriatr Soc. 2026. doi:10.1111/jgs.70600
2. Caffrey M. Study of BMI, death rates over time debunks "obesity paradox." AJMC^®. April 4, 2017. Accessed August 19, 2026. https://www.ajmc.com/view/study-of-bmi-death-rates-over-time-debunks-obesity-paradox