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Study sheds new light — and more controversy — on childhood obesity statistics

REUTERS/John Vizcaino
The new study found that the obesity rate dropped slightly between 1999 and 2011, but that change may be due only to chance.

When researchers at the U.S. Centers for Disease Control and Prevention (CDC) reported earlier this year that the obesity rate among preschoolers had plummeted a dramatic 43 percent over the past decade, they warned people to interpret that statistic with caution.

They also stressed that the study had uncovered a troubling overall finding: The U.S. obesity rates for both youth and adults has barely budged at all during the past decade. Almost 35 percent of U.S. adults and 17 percent of children and teens were obese in 2012.

But, of course, it was the drop in the obesity rate among preschoolers that soaked up much of the media attention given to the study. (I certainly led with it in my report.) That frustrated many obesity specialists who were worried that the public might find the CDC’s report so reassuring that it would “change the national discourse” about what needs to be done to reduce child obesity.

They also believed the 43 percent drop was simply a statistical fluke.

Expanding the data set

A new study, published online Monday in the medical journal JAMA Pediatrics, may help clarify the issue. It used the same source of data (the National Health and Nutrition Examination Survey) as the CDC researchers, but went back a few more years. Whereas the CDC study examined data from the years 2003 to 2012, the new study looked at the years 1999 to 2012.

By using a different starting point, the drop in the rate of obesity among preschoolers became less significant, the new study found.

“In 2003 there was an unusual spike in the number [of obese preschoolers] for whatever reason — probably an error,” the study’s lead author, Asheley Cockrell Skinner of the University of North Carolina at Chapel Hill, told Reuters reporter Andrew Seaman. “When you take a long view from 1999 to now, you don’t see that decline.”

Or, at least not a significant decline. The new study found that the obesity rate dropped slightly between 1999 and 2011, but that change may be due only to chance.

The analysis conducted by Skinner and study co-author Dr. Joseph Skelton of Wake Forest University, does concur, however, with the CDC researchers’ overall finding that the obesity rate among children of all ages has been holding pretty steady at the 17 percent figure for the past decade or so.

Severe obesity on the rise

That might seem reassuring. At least the rate isn’t going up. But by digging deeper into the data, Skinner and Skelton unearthed a worrisome new finding: The rate of severe (class 2) obesity among children and teens increased from 3.8 percent to 5.9 percent between 1999 and 2012. And the rate of severest (class 3) obesity rose from 0.9 percent to 2.1 percent.

Class 2 obesity is generally defined as having a body-mass index (BMI) of 35 to 39, while class 3 obesity is defined as a BMI equal to or greater than 40.

“Examining only the total prevalence of overweight and obesity among children masks upward trends of class 2 and class 3 obesity across time,” Skinner and Skelton write in their study’s conclusion. “Although our results suggest that the prevalence of obesity is continuing to level off, research is needed to determine which, if any, public health interventions can be credited with this stability. Unfortunately, the high prevalence and upward trend of more severe forms of obesity will likely require more intensive interventions than can be done through widespread public health efforts.”

Needed: aggressive interventions

Those severely obese kids are the ones we should worry about most, Skinner told reporter Kim Painter of USA Today. That’s because the severer the obesity, the greater the health risks — and not just later in adulthood. Obese children are at an increased risk of developing many immediate health problems, such as high blood pressure, high glucose levels (which can lead to type 2 diabetes), bone and joint problems, sleep apnea and depression.

Helping those children is going to require innovative and aggressive public-health interventions.

“You can’t just tell that kid to eat more fruits and vegetables and everything will be better,” said Skinner.

You’ll find an abstract of Skinner’s study on the JAMA Pediatrics website, but the study itself is behind a paywall.

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