Research published Monday online in the journal Epidemiology found that nearly 20 percent of U.S. young adults have high blood pressure.

That’s far higher than the last national estimate, which had put the number at 4 percent.

High blood pressure, or hypertension, is a key risk factor for coronary heart disease, which is the leading cause of death in among adults in the United States.

Researchers analyzed data for more than 14,000 men and women between 24 and 32 years old in 2008 from the National Longitudinal Study of Adolescent Health, funded by the National Institutes of Health. That survey, known as Add Health, was the first to look specifically at high blood pressure among young adults; the condition is typically associated with older people. In addition to finding that 19 percent of young adults had high blood pressure (defined as a reading of 140/90), the survey revealed that only about half of those with high blood pressure had been told before by a physician that their blood pressure was high.

The National Health and Nutrition Examination Survey ( NHANES), conducted about the same time as the Add Health one (in 2007-2008), identified just 4 percent of the young adult population as having high blood pressure. And, oddly, twice that number had reported a history of high blood pressure. The researchers looked at the discrepancy between the Add Health figure and the NHANEs one but came up with no explanation that could account for the wide gap between them.

Whether it’s 19 percent or 4 percent, though, the researchers suggest that both surveys point to the need to monitor young people’s blood pressure. Early diagnosis and treatment could forestall many of the problems associated with hypertension, they note.