Measuring waist circumference predicts heart attack and stroke risk far better than body mass index alone, researchers at Johns Hopkins Ciccarone Center have found.
The study showed that measuring a person's waist circumference and waist-to-hip ratio accurately identified those at significantly higher risk of nine major cardiovascular conditions. These include heart attack, stroke, heart failure, atrial fibrillation, coronary heart disease, general cardiovascular disease, and death from any cause.
Researchers examined the health records of 260,000 participants over a 20-year period in work published in the Journal of the American College of Cardiology. Their analysis revealed that relying on body mass index alone leaves up to a fifth of normal-weight individuals unaware of dangerous underlying health risks.
Limitations of body mass index
Body mass index, known as BMI, is calculated by dividing an adult's weight in kilograms by height in metres squared. It is the standard metric used by healthcare systems worldwide to determine whether an individual maintains a healthy weight.
In the United Kingdom, around one-third of adults are classified as obese, defined as having a BMI score over 30. Obesity carries a well-established risk of severe long-term complications, including type 2 diabetes and various forms of cancer.
Medical experts have long argued that BMI provides an incomplete picture of overall health. The metric fails to distinguish between muscle mass and fat, and it does not measure where fat is stored on the body.
Fat carried around the stomach, known as central adiposity, is a primary driver of organ damage. This includes visceral fat, which wraps around vital internal organs such as the liver and pancreas. While every human body contains some visceral fat, excess accumulation disrupts organ function and triggers life-threatening conditions.
Key findings on central fat
The US study measured participants' waist circumference and waist-to-hip ratio alongside their BMI scores. The results demonstrated striking gaps in traditional risk assessment.
Among participants categorized as having a healthy weight under BMI standards, 18 per cent possessed a worryingly high waist-to-hip ratio. Furthermore, 5 per cent of normal-weight participants had a dangerously high waist circumference.
Participants with an unusually high waist measurement or waist-to-hip ratio faced a 15 to 50 per cent higher risk across most of the nine cardiovascular outcomes tracked by the researchers.
Conversely, BMI frequently overestimated risk in heavier individuals. Only around four in ten participants classified as overweight by BMI had a high waist-to-hip ratio. Among those classified as obese, only about half had elevated waist-to-hip ratios.
Critically, obese individuals with a smaller waist carried no higher risk of heart problems than normal-weight individuals with a similarly sized waist. Researchers warned that relying solely on BMI causes clinicians to misjudge patient risk in both directions.
Expert calls for clinical changes
Michael J. Blaha, senior author of the study and director of clinical research at the Johns Hopkins Ciccarone Center for the Prevention of Cardiovascular Disease, emphasized the clinical implications of central fat.
"We saw individuals with clinically determined normal weight who had elevated central adiposity and high [waist-to-hip ratio], associating them with higher risk across most outcomes," Blaha said.
Zeina Dardari, lead author of the study from the Johns Hopkins Ciccarone Center, urged doctors to update how they assess patients.
"Relying solely on BMI may result in misclassification of cardiovascular risk across a wide range of cardiovascular outcomes," Dardari said. "We encourage clinicians to consider central adiposity distribution across the entire BMI spectrum when evaluating cardiovascular risk."
Harlan M. Krumholz, editor-in-chief of the Journal of the American College of Cardiology and a scientist at Yale School of Medicine, described the findings as a turning point for routine medicine.
"It is time to abandon a sole focus on BMI," Krumholz said. "This enormously important study, based on data from hundreds of thousands of participants, authoritatively shows that waist circumference and waist-to-hip ratio provide critical information about cardiovascular risk, even among people with a BMI considered normal."
"Where fat is distributed matters, and these simple measures should be part of routine cardiovascular risk assessment," Krumholz added.
Study limitations
The research team noted several limitations in their study design. The dataset did not track participants' physical activity levels, dietary habits, or genetic predisposition to obesity, all of which influence cardiovascular health.
Additionally, waist measurements were recorded only once at the start of the 20-year observation period. As a result, the researchers could not evaluate how changes in body fat over time might affect individual risk levels.
How to calculate waist to hip ratio
Waist circumference measures the distance around the abdomen. The waist-to-hip ratio compares that figure to hip circumference, providing a clear picture of fat distribution in the lower middle of the body.
Health experts advise using a soft measuring tape to perform the test. To measure waist circumference, place the tape around the smallest part of the waist, located just above the belly button area. To measure hip circumference, wrap the tape around the largest part of the hips, across the widest point of the buttocks.
The waist-to-hip ratio is calculated by dividing the waist circumference by the hip circumference. Official government guidance states that a healthy waist circumference should measure less than half of a person's height.
According to the World Health Organization, a waist-to-hip ratio above 0.9 indicates increased health risk for men, while a ratio above 0.85 poses a danger for women.
