Can neck measure indicate body fat better than BMI?
(CNN) — Flawed, limited and inaccurate. The complaints against the body mass index are many.
Among them: The BMI, which measures weight relative to height, doesn’t accurately calculate body fat. It deems athletes or muscular people to be obese and underestimates body fat in older people.
But it’s inexpensive and simple, so the BMI continues to be the public health agencies’ standard for assessing for obesity.
A study published Monday in the journal Pediatrics suggests another simple, straightforward measurement could be used to supplement the BMI: neck circumference.
A wide neck circumference is associated with obesity-related conditions such as sleep apnea, diabetes and hypertension, according to research. Neck circumference has been explored in studies for potential obesity and heart problems in adults.
Lead author Dr. Olubukola Nafiu and his colleagues examined 1,102 children and recorded their heights, weights and neck circumferences to determine whether this measurement could be another way to assess obesity in children.
They measured necks using a flexible tape at the most prominent part of the neck. For older males, that area was the Adam’s apple.
Based on age, a neck of this circumference or larger could indicate overweight or obesity, researchers say:
Age 6: 11.2 inches
Age 10: 12.6 inches
Age: 14: 14.2 inches
Age 18: 15.4 inches
Age 6: 10.6 inches
Age 10: 12 inches
Age 14: 12.6 inches
Age 18: 13.6 inches
The authors found that a 6-year-old boy with a neck circumference greater than 11.2 inches was 3.6 times more likely to be overweight or obese than a peer below that level. Using the data, they devised neck measurements at which children could be at higher association with overweight and obesity.
Taking such a measurement is inexpensive, easy and could be predictive of health problems such as sleep apnea, Nafiu wrote in the article. He’s an assistant professor of pediatric anesthesia at the University of Michigan School of Medicine Health, Ann Arbor.
One of BMI’s shortcomings is that it “does not accurately define central body fatness,” Nafiu said. Neck circumference could give better clues to body fat composition, he said.
Studies have shown that regional adiposity, which is fat collected around the midsection, is often a good indicator for obesity-related complications, including hypertension, diabetes and heart disease. The correlation between regional adiposity and a high neck circumference is strong, said Nafiu. This could give doctors more information than BMI alone.
“We’ve been using BMI to advise parents and patients for making healthy choices,” he said. “Unfortunately, often we tell someone their BMI is 27 or 30, most of the time it doesn’t mean much. To tell you that your neck is wide, these are some of the risks associated to it — that we feel people would be able to relate to it better than BMI.”
The idea of using circumferences of various body parts has been around for awhile, said Jim Pivarnik, director of the Center for Physical Activity and Health at Michigan State University.
“It’s not widely used,” he said. “It doesn’t mean it’s not correct, but it’s not widely used.”
One of the challenges is the difficulty of accurate measurements. Waist circumference “is harder to measure than you might think,” said Dr. Cora Lewis, a professor of medicine and public health at the University of Alabama at Birmingham.
“There’s the issue of figuring out where you measure,” she said. “If someone is obese, should the waist measurement come under or over the fold?”
Despite its flaws, Lewis said the BMI still gives information.
“It’s a good place to start,” she said. “Lots of people bash it, but what else are we going to use?”
The alternatives, such as air chambers that measure a person’s mass and volume to calculate the composition of muscle and fat and underwater scales, are expensive and impractical, Pivarnik said.
The neck circumference could an initial screening tool someday, Nafiu said. But he wrote additional studies are needed to evaluate how useful it is in detecting abdominal fat.
“If a neck circumference is above what you regularly see, that raises a red flag,” he said. “You want to ask further questions, then see other indices of body fat — BMI, abdominal circumference and other parameters.”