Neck Circumference Most Reliable Alternative to BMI for Childhood Obesity

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Body mass index (BMI) is the most used marker of both adult and childhood obesity, but the calculation is flawed and not a good indicator of body fat. Researchers from the University of Michigan, Ann Arbor, have found that neck circumference, more than any other screening technique, was the most reliable alternative to BMI for identifying obese children.

Body Mass Index, originally known as the Quetelet index, was invented to be used as a screening tool for population studies, but is more and more used inappropriately for individual diagnosis of weight problems.

“The body mass index doesn’t tell you what is responsible for someone’s weight. In some cases, it could all come from muscle [or large bones], but your BMI could still indicate that you are overweight,” said lead author Dr. Olubukola “Bukky” Nafiu.

BMI also does not indicate location of adiposity. People with “apple shapes”, or those with excessive fat tissue around the abdomen, are at a greater risk of health problems such as high blood pressure, diabetes, and high cholesterol than those with “pear shapes” – weight primarily located in the hips and thighs.

Dr. Nafiu and colleagues studied 1,102 children divided into four categories by age and sex. They measured neck circumference as well as height, weight, waist circumference and BMI. Neck circumference was measured with a flexible tape, with the children in a standing position and their heads held erect

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The researchers found neck circumference to be more accurate than BMI because of the strong correlation between high neck circumference measurements and central adiposity (fat around the abdomen). The technique was also more convenient than waist circumference, and more consistent as the abdomen can swell after a large meal.

The researchers also pinpointed "optimal" cutoff points for neck circumference that identified a majority of kids with a high BMI, which are listed below based on age:

Boys
Age 6: 11.2 inches
Age 10: 12.6 inches
Age: 14: 14.2 inches
Age 18: 15.4 inches

Girls
Age 6: 10.6 inches
Age 10: 12 inches
Age 14: 12.6 inches
Age 18: 13.6 inches

In addition to obesity screening, the researchers note that neck measurements might also be useful for spotting kids at risk of sleep apnea, a disorder in which tissues at the back the throat temporarily collapse during sleep to create repeated stops and starts in breathing. Obesity, particularly excess weight in the upper body, is a risk factor.

Neck circumference may not work as well in adults because the possibility of a child having an excessively muscular neck is not likely to be a problem, but some athletic adults, particularly body builders, may develop large neck muscles skewing the results.

Screening for childhood obesity is recommended by the US Preventive Services Task Force to begin at age 6.

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