Despite obesity rise, kids' blood pressure dipped

The rate of childhood obesity may have soared between the 1970s and 90s, but kids' blood pressure did not follow the same trend, a U.S. government study suggests.

Researchers at the Centers for Disease Control and Prevention (CDC) found that while the obesity rate among Louisiana children nearly tripled between 1974 and 1993, their blood pressure actually improved a bit.

Among nearly 11,500 children and teens assessed over those 20 years, the rate of obesity rose from 6 percent to 17 percent.

But their blood pressure, on average, remained fairly stable. And far fewer children than expected actually had high blood pressure by 1993: about 4 percent of boys and 6 percent of girls.

By comparison, those numbers were about 6 percent and 8 percent, respectively, in 1974.

None of that means that obesity is harmless to kids, said lead researcher David S. Freedman, of the CDC's division of nutrition, physical activity and obesity.

"Maybe the biggest problem is that obese children usually become obese adults," said Freedman. Past research, he noted, has found that about 75 percent of obese kids are obese as adults as well.

And at that point, obesity carries an increased risk of chronic conditions like type 2 diabetes, heart disease and arthritis.

Height related to blood pressure

In the U.S., obesity -- in adults and kids, alike -- had its biggest surge between the 1970s and 90s, Freedman said.

Since then, things have leveled off. Among teenagers, for example, the obesity rate hovered between 18 and 20 percent in the decade between 1999 and 2008, according to another recent CDC study.

Blood pressure does tend to rise along with body mass index (BMI) -- a measure of weight in relation to height.

But studies have had mixed findings on whether the rise in childhood obesity spurred any increase in kids' blood pressure.

A problem with some past research, according to Freedman, is that it failed to account for the fact that kids have also gotten taller over the years. Height, Freedman said, is a stronger influence over kids' blood pressure than is weight.

"I think the take-home from this study is that we should not necessarily assume that increases in childhood obesity will be associated with changes in every risk factor," Freedman said.

Better nutrition?

So why didn't blood pressure rise along with kids' weight?

This study, published in the journal Pediatrics, cannot show the reason, Freedman said. In theory, he noted, it could have to do something with improvements in early childhood nutrition -- including rising breastfeeding rates. But that's speculation for now.

One area where kids are not doing better is type 2 diabetes.

Last month, a CDC study found that among U.S. teenagers, the prevalence of type 2 diabetes and "pre-diabetes" -- a precursor to type 2 -- rose from 9 percent in 1999-2000, to 23 percent in 2007-2008.

Type 2 diabetes is closely associated with obesity. But the rise in teen diabetes came at a time when the obesity rate held steady. The CDC researchers were not sure of the reasons.

But they said the bottom line for parents and kids remains the same: Eat a balanced diet and get regular exercise.

The U.S. Preventive Services Task Force, a government-backed panel, recommends that children age 6 and older be screened for obesity. If a child is heavy, pediatricians should offer families behavioral counseling, or refer them to someone who can.