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By Brian Alexander
Ethan Borst, 15, was overweight and has had sporadic high blood pressure. After attending a camp designed to help kids lose weight, he is on the right track to health.NBC News

Spurred by too much salt and too many extra pounds, blood pressure in America's kids and teens has gone sky-high, creating a young generation at risk for serious health problems, including heart disease, stroke -- and worse.

The percentage of American children and adolescents ages 8 to 17 who have high blood pressure -- a risk factor for cardiovascular disease, organ damage, heart attacks and strokes -- climbed 27 percent over 13 years, according to researchers from Harvard Medical School, Brigham and Women's Hospital and other institutions funded by the National Institutes of Health.

The researchers, using two large national surveys, compared blood pressure data of thousands of children from two National Health and Nutrition Examination Surveys, a government program designed to track health and nutritional status of adults and children in the U.S. During the period 1988 to 1994, 15.8 percent of boys, and 8.2 percent of girls could be classified as having elevated blood pressure. By the next survey period, covering the years 1999-2008, those percentages jumped to 19.2 percent for boys and 12.6 percent for girls.

The new research, published Monday in the journal Hypertension, positively links rising blood pressure to increasing body mass index, especially waist circumference, and sodium intake. In short, far too many American children are too fat and eating too many salty snacks.

More than a third of children and teens in the United States are overweight or obese, according to the Centers for Disease Control and Prevention. “The reason we’re seeing high blood pressure in kids, is due to the obesity epidemic,” said pediatrician Dr. Joanna Dolgoff.

Dolgoff has been seeing elevated blood pressure in so many of her young patients, she thought her equipment was broken.

"Recently, I've been a lot more of my patients having high blood pressure," Dolgoff, a child obesity expert and creator of the “Red Light, Green Light, Eat Right” nutrition program, said. "I thought perhaps my blood pressure machine was broken. But actually the incidence of high blood pressure in children is increasing."

Being overweight is a key risk factor for high blood pressure in adults so “it stands to reason that it would be the same in children,” said Dolgoff.

Ethan Borst, 15, of New York, N.Y., started gaining weight when he was just 7. Although high blood pressure and diabetes run in his family, his mother, Renee Katz, was surprised to discover Ethan had high blood pressure at such a young age.

"I wanted to make sure that he wasn't going to have those problems when he gets older." After attending a weight-loss camp run by Dolgoff, Ethan lost almost 30 pounds and has given up his favorite salty snacks.

"I do enjoy corn chips, but I try to stay away from those," Ethan said.

The researchers found that “for total fat, saturated fat, and protein, a large majority of children (70 percent to 80 percent) were above the RDI [recommended daily intake],” the study found. For sodium intake, “over 80 percent” of the children were above the RDI.

“Kids eat far too much sodium,” the study's co-author Dr. Stephen Daniels told NBC News. “And they aren’t adding it at the table, and their parents aren’t putting it into food; they’re getting it through processed foods.”

Past studies have indicated blood pressure among America’s youth might be on the rise, but most used small samples. The NHANES data in this research was made up of 3,248 children for the period 1988 to 1994 and 8,388 for the 1999-2008 survey.

The damage from far too much dietary sodium has been especially pronounced in African-American girls, accounting for much of the higher rate of increase in girls compared to boys, said Daniels, chair of the Department of Pediatrics at the University of Colorado School of Medicine, and the chair of the National Heart, Lung and Blood Institute’s panel that created guidelines for cardiovascular health and risk reduction in children.

“On some level we know there has been some relationship between obesity and blood pressure and some previous studies showed that blood pressure has risen over time,” Daniels said.

Dr. Patrick McBride, a cardiologist, agrees.

“It’s all nutritionally related and activity related,” said McBride, professor of medicine and family medicine and associate director of preventive cardiology at the University of Wisconsin School of Medicine and Public Health. “Children are being parked in front of screens, videos, electronics and then consuming high-caloric-density foods.”

As a result, some have the cardiovascular damage more common in middle-aged and older people.

“I have had a heart disease prevention practice for 30 years,” McBride said, “and we only used to see high blood pressure rarely in children. Now it’s common. Every week I see high blood pressure, high cholesterol. It’s astounding.”

The damage isn’t just long-term, with heart attacks and strokes at ages 25 or 30. McBride can see physical damage in the children. “With ultrasound on the carotid artery, we can see early atherosclerosis,” he said.

Daniels explained that children can also show signs of an enlarged heart ventricle because the heart has to work harder to push blood.

Both Daniels and McBride explained that pediatricians and family physicians should be more diligent about checking blood pressure in children, and, if dietary and exercise advice don't work, consider prescribing blood pressure-lowering drugs.

NBC "Nightly News" producer Jane Derenowski contributed to this report