Publish date: September 20, 2022
Waist-hip ratio beats BMI for predicting obesity’s mortality risk
STOCKHOLM – New evidence continues to show that alternative measures of adiposity than body mass index, such as waist-to-hip ratio, work better for predicting the risk a person with overweight or obesity faces from their excess weight.
A direct comparison of waist-to-hip ratio (WHR), body mass index (BMI), and fat mass index (FMI) in a total of more than 380,000 United Kingdom residents included in the UK Biobank showed that WHR had the strongest and most consistent relationship to all-cause death, compared with the other two measures, indicating that clinicians should pay more attention to adiposity distribution than they do to BMI when prioritizing obesity interventions, Irfan Khan said at the annual meeting of the European Association for the Study of Diabetes.
Although it’s likely “way too early” to fully replace BMI as a measure of adiposity, because it is so established in guidelines and in practice, it is now time to “use WHR as an adjunct to BMI” suggested Mr. Khan in an interview.
“A lot of work still needs to be done to translate WHR into practice, but I think it’s getting closer,” said Mr. Khan, a medical student at McMaster University, Hamilton, Ont., who performed his analyses in collaboration with a research team based primarily at McMaster.
Moving away from BMI-centric obesity
“This is a timely topic, because guidelines for treating people with obesity have depended so much on BMI. We want to go from a BMI-centric view to a view of obesity that depends more on disease burden,” commented Matthias Blüher, MD, professor of molecular endocrinology and head of the Obesity Outpatient Clinic for Adults at the University of Leipzig (Germany).
For example, the 2016 obesity management guidelines from the American Association of Clinical Endocrinologists and the American College of Endocrinology called for a “complications-centric” approach to assessing and intervening in people with obesity rather than a “BMI-centric” approach.
But Dr. Blüher went a step further in an interview, adding that “waist-to-hip ratio is now outdated,” with adjusted measures of WHR such as waist-to-height ratio “considered a better proxy for all-cause death.” He also gave high marks to the Edmonton Obesity Staging System, which independently added to BMI as well as to a diagnosis of metabolic syndrome for predicting mortality in a sample from the U.S. National Health and Nutrition Examination Survey (NHANES). The Edmonton System also surpassed BMI for disease-severity staging using data from more than 23,000 Canadians with a BMI that denoted obesity.
1 standard deviation increase in WHR linked with a 41% increased mortality
The study reported by Mr. Khan used both epidemiologic and Mendelian randomization analyses on data collected from more than 380,000 U.K. residents included in the UK Biobank database to examine the statistical associations between BMI, FMI, and WHR and all-cause death. This showed that while BMI and FMI both had significant, independent associations with all-cause mortality, with hazard ratios of 1.14 for each 1 standard deviation increase in BMI and of 1.17 for each standard deviation increase in FMI, the link was a stronger 1.41 per standard deviation increase in WHR, he said.
Another analysis that divided the entire UK Biobank study cohort into 20 roughly similar subgroups by their BMI showed that WHR had the most consistent association across the BMI spectrum.
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Further analyses showed that WHR also strongly and significantly linked with cardiovascular disease death and with other causes of death that were not cardiovascular, cancer-related, or associated with respiratory diseases. And the WHR link to all-cause mortality was strongest in men, and much less robust in women, likely because visceral adiposity is much more common among men, even compared with the postmenopausal women who predominate in the UK Biobank cohort.
One more feature of WHR that makes it an attractive metric is its relative ease of measurement, about as easy as BMI, Mr. Khan said.
The study received no commercial funding, and Mr. Khan had no disclosures.
Dr. Blüher has been a consultant to or speaker on behalf of Amgen, AstraZeneca, Bayer, Boehringer Ingelheim, Lilly, Novartis, Novo Nordisk, and Sanofi.