Although pediatric high cholesterol levels in the U.S. have gone down since 1999, about one in 10 kids still has high blood pressure, according to a new study.

By 2012, approximately 20 percent of U.S. kids ages 8 to 17 had unhealthy cholesterol levels, and 10 percent had hypertension or borderline hypertension.

These measures tend to track from childhood into adulthood, and in adults they are associated with heart problems and death, the authors note in the introduction to their JAMA Pediatrics report.

“Our research suggests there were modest improvements in blood cholesterol levels and stable blood pressure levels among children between 1999 and 2012,” lead author Dr. Brian K. Kit told Reuters Health.

“Because cholesterol levels and blood pressure in childhood are associated with cholesterol levels and blood pressure in adulthood, changes during childhood may have long-term significance,” said Kit, who is with the U.S. Public Health Service at the National Center for Health Statistics in Hyattsville, Maryland.

For the new study, Kit and his colleagues used National Health and Nutrition Examination Survey (NHANES) data, which includes direct measurements of fat and cholesterol in the blood and blood pressure readings, from seven surveys between 1999 and 2012.

The analysis looked at blood cholesterol data and blood pressure readings for about 1,500 kids ages eight to 18.

In the most recent survey, conducted in 2011-2012, some 20 percent of the kids had an “adverse lipid concentration” - meaning they had high total cholesterol, high bad cholesterol or low good cholesterol. Eleven percent had high or borderline-high blood pressure readings, based on cutoff points for the child’s sex, age and height.

Unhealthy cholesterol levels had become a little less common since the 1999 survey. For example, in 1999 just over 10 percent of kids had high total cholesterol, which fell to 7.8 percent in 2012.

There were also fewer kids with high blood pressure over the decade, a decrease from 3 percent to 1.6 percent. But the number of kids with borderline high blood pressure remained steady, and when the borderline and high categories were lumped together, these too were steady from 1999 to 2012.

“Cholesterol levels and blood pressure are influenced by many factors including diet, physical activity and exposure to smoke,” Kit told Reuters Health by email.

The study didn’t explore why rates of unhealthy cholesterol and blood pressure had declined or plateaued. And Kit noted that complications from those conditions are uncommon during childhood.

But, he emphasized, screening and prevention in kids and teens is important to prevent these important heart disease risk factors form persisting into adulthood.

Bernard Rosner, professor of biostatistics at the Harvard School of Public Health in Boston, noted that in a similar study he conducted, almost twice as many kids qualified for high blood pressure because he used blood pressure standards based on healthy-weight children.

The new study, in which he was not involved, used standards based on a combination of healthy-weight and overweight children, Rosner noted.

Rosner also cautioned that the demographics of the NHANES survey sample may have changed over time, which might explain some of the shifts in rates of adverse cholesterol or blood pressure.

The National Institutes of Health have issued guidance for pediatricians to help kids with high cholesterol or high blood pressure improve their diets or physical activity or for prescribing medications for them, Kit said.