The rate of childhood obesity in the United States may have soared between the 1970s and the 1990s, but children’s blood pressure did not follow the same trend, according to a study.

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

“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,” said lead researcher David Freedman of the CDC’s division of nutrition, physical activity and obesity.

Among nearly 11,500 children and teens assessed over the 20 years of the study, which appeared in the journal Pediatrics, the rate of obesity rose from 6 percent to 17 percent.

But 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, the number with high blood pressure in 1974 was about 6 percent and 8 percent.

None of that means obesity is harmless in children, Freedman said, noting that about 75 percent of obese children are obese as adults - and with an increased risk of chronic conditions like type 2 diabetes, heart disease and arthritis.

“Maybe the biggest problem is that obese children usually become obese adults,” he added.

In the United States, obesity - in adults and children alike - had its biggest surge between the 1970s and 1990s, but since then has leveled off.

Blood pressure does tend to rise along with body mass index (BMI), a measure of weight in relation to height, but previous studies had mixed findings on whether the rise in childhood obesity spurred any increase in blood pressure.

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

But Freedman said the current study cannot show the reason why blood pressure didn’t rise along with obesity. In theory, it could have something to do with improvements in early childhood nutrition, such as rising breastfeeding rates - but that is just speculation at this point.

A CDC study last month 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. But given that obesity rates held steady, they weren’t sure why.

In any case, researchers said the bottom line for parents and children remains the same - eat a balanced diet and get regular exercise.

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