Waist-Height Ratio Better Than BMI for Gauging Mortality

Estimates of years of life lost due to obesity were higher and more accurate when using waist-to-height ratio (WHtR) than body mass index (BMI), according to a new study.

Researchers at Oxford Brookes University (United Kingdom) compared the effect of central obesity, as measured by WHtR, and total obesity, as measured by BMI, on life expectancy, expressed as years of life lost. The researchers then created a Cox proportional hazards model using data from the Health Survey for England and the Health and Lifestyle Survey, calculating years of life lost at ages 30, 50, and 70 by comparing the life expectancies of obese patients with those lives at optimum levels of BMI and WHtR.

The researchers found that overall, mortality risk was associated with BMI, but WHtR estimates were higher and appeared to be a more accurate indicator. For example, a 30-year-old man with a BMI in the highest category—over 40 kg/m2—has a years-of-life-lost value of 10.5 years, but as measured using the WHtR method, he has a value of 16.7 years. A 30-year-old woman had a years-of-life-lost value of 5.3 years, compared with a value of 9.5 years when using WHtR. And a 50-year-old man in the most severe category of BMI has a years-of-life-lost value of 9.7 years, compared with 12.1 years when using the most severe category of WHtR. The study was presented at the European Congress on Obesity, held during May 2013 in Liverpool (United Kingdom).

“The use of WHtR in public health screening, with appropriate action, could help add years to life,” said Margaret Ashwell, PhD. “If health professionals included this simple measurement in their screening procedures, then many years of productive life could be saved.”

The WHtR of a person is defined as the person's waist circumference, divided by the person's height, and measures the distribution of body fat. Higher values of WHtR indicate higher risk of obesity-related cardiovascular diseases. For people under 40, a WHtR of over 0.5 is critical; for people in the age group between 40 and 50 the critical value is between 0.5 and 0.6, and for people over 50 the critical values start at 0.6.

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