The body mass index (BMI) isn't a perfect measure for obesity. Convenience and routine are on its side — so health experts aren't likely to stop using it any time soon — but its limitations have got some doctors thinking … .
In a study published online Monday in the journal Pediatrics, researchers at the University of Michigan’s Mott Children’s Hospital found measurements of neck circumference to be a reliable technique for assessing whether children are overweight or obese.
Using a sample pool of 1,102 children (divided into four categories — 6 to 10 years of age and 11 to 16 years of age, male and female), the team studied the correlation of kids' neck circumference with measurements of their heights, weights and waist circumferences, as well as with their ages and BMI statistics.
The results confirmed that -- more than any other screening technique -- neck circumference was the most reliable alternative to BMI, when adjusted to a child’s age and gender. But the findings went one step further than that, said Dr. Olubukola “Bukky” Nafiu, who led the study,Measuring neck circumference was more convenient and was more accurate than BMI at identifying children with weight problems, he said.
“The body mass index doesn’t tell you what is responsible for someone’s weight. In some cases it could all come from muscle, but your BMI could still indicate that you are overweight,” he said. The possibility of a child having an excessively muscular neck that may skew results is not a problem as it can be with adults, some of whom develop big, muscle-bound necks, he added.
Fat distribution is another problem associated with reliance on the BMI. Researchers are beginning to learn more about how fat on the body can lead to different degrees of health risks depending on the area of accumulation -- fat around the middle, in particular, is associated with raised risk for high blood pressure, diabetes and high cholesterol.. Said Nafiu, “The BMI doesn’t tell you where the fat in someone’s body is collected."
And necks? There's a strong correlation, Nafiu says, between high neck circumference measurements and central adiposity (fat around the middle).
Nafiu believes that the defects associated with BMI measurements -- as well as the inconvenience and embarrassment for kids of clothing removal and the higher potential for error in height and weight measurements -- will lead doctors to adopt alternative methods for obesity screening in both children and adults.
“In the next few years, I believe more and more doctors will start screening for obesity and overweight using neck circumference measurements and other methods, instead of the BMI,” he said.
-- Jessie Schiewe