What the 15-Cohort Study Found Beyond BMI

A pooled analysis of 259,388 adults from 15 U.S. cohort studies has found that waist circumference and waist-to-hip ratio reveal meaningful cardiovascular risk differences that body mass index alone can hide. Among people classified as normal weight or overweight by BMI, a large waist or high waist-to-hip ratio was associated with 15% to 50% higher risk for most heart disease outcomes over roughly two decades.

The researchers examined first fatal or nonfatal heart attacks, strokes, heart failure, atrial fibrillation, total coronary heart disease, total cardiovascular disease and deaths. High waist circumference was defined as more than 88 cm for women and more than 102 cm for men; high waist-to-hip ratio was defined as above 0.85 for women and above 0.90 for men. Normal weight was a BMI of 18.5 to below 25, overweight was 25 to below 30, and obesity was 30 or above.

Strikingly, adults with obesity but a smaller waist had clinical outcomes largely similar to normal-weight adults, and some had lower all-cause mortality risk. The authors, led by Michael Blaha of Johns Hopkins, concluded that waist measurement should be considered across the entire BMI spectrum in primary prevention. The findings build on the American Medical Association's 2023 caution against using BMI alone and a Lancet Commission recommendation to confirm obesity with another measure such as waist circumference or waist-to-hip ratio.

Why Waist Distribution Changes the Cardiovascular Risk Conversation

Where BMI Alone Misclassifies Cardiac Risk

The prevalence data show how much heterogeneity exists inside conventional BMI groups. Among normal-weight participants, 5% had a large waist and 18% had a high waist-to-hip ratio. Among overweight participants, 39% had a large waist and 40% had a high waist-to-hip ratio. Among those with obesity, 9% had a small waist and 45% had a low waist-to-hip ratio. That means two people with the same BMI can carry substantially different cardiovascular risk depending on where fat is distributed.

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How Much Risk Is Linked to Central Adiposity

For people with obesity, the population attributable risk tied to a large waist or high waist-to-hip ratio ranged from 13% to 49%. The strongest associations were with heart failure and atrial fibrillation. The researchers interpret this as evidence that waist measures add diagnostic and prognostic information to BMI categories, rather than simply repeating what BMI already shows. Because the study is observational, it demonstrates association, not proof that reducing waist size independently prevents cardiovascular events.

The Sex-Specific Finding Researchers Flagged

The authors reported that women with obesity and a low waist-to-hip ratio still had higher risk for the studied outcomes than normal-weight women with a low waist-to-hip ratio, although their risk was lower than women with obesity and a high ratio. Men showed a different pattern. This suggests that sex-specific interpretation of central adiposity may matter for clinical risk assessment, and the authors list sex differences as an area needing further study.

Why Major Guideline Voices Are Moving in This Direction

The study arrives after the American Medical Association advised against relying on BMI as a standalone diagnostic tool and after a Lancet Commission recommended that clinical obesity diagnoses be verified with at least one additional measure. JACC Editor-in-Chief Harlan Krumholz said the findings show that where fat is distributed matters and that waist circumference and waist-to-hip ratio should be part of routine cardiovascular risk assessment. The editorial accompanying the study said the relative contribution of waist circumference to specific cardiovascular endpoints had been a key knowledge gap.

Waist-Based Risk Tools for Clinics, Patients and Guidelines

  • For primary care clinicians: Add waist circumference and waist-to-hip ratio to cardiovascular assessment across the full BMI range, not only for patients classified as overweight or obese. The study found that 5% of normal-weight adults had a large waist and 18% had a high waist-to-hip ratio, groups carrying excess risk.
  • For patients: Ask for a waist measurement and waist-to-hip ratio at your next cardiovascular check, especially if your BMI is normal or overweight but weight is carried around the middle.
  • For health systems and guideline committees: Model how central adiposity variables can be integrated into existing cardiovascular risk tools. Among people with obesity, a large waist or high waist-to-hip ratio was associated with a 13% to 49% population attributable risk, strongest for heart failure and atrial fibrillation.
  • For researchers: The unresolved questions are longitudinal: whether reducing central adiposity independently lowers cardiovascular risk, how often waist measures should be repeated, and which sex-specific thresholds are most useful. Current findings support measurement, not yet a proven standalone treatment target.