High blood pressure is a treatable factor for heart attack and stroke, but about one-quarter of adults don't know they have it, according to a large new study, Newsmax Health reports.

Among those who do know they have the condition, many are not likely to have it under control, said lead researcher Dr. Uchechukwu Sampson, a cardiologist at Vanderbilt University Medical School in Nashville.

In Sampson's study, the researchers evaluated how common high blood pressure was in more than 69,000 men and women. Overall, 57 percent self-reported that they had high blood pressure.

"Among those who reported a history of high blood pressure, more than half of blacks and nearly half of whites had uncontrolled blood pressure," Sampson said. "Among those who did not report a history of high blood pressure, nearly a third of blacks and nearly a quarter of whites had high blood pressure but were unaware of it."

An expert who reviewed the research said the findings show that high blood pressure is extremely common, and it might not be being treated according to the recommended guidelines.

"This study points out that high blood pressure is still a huge problem in this country," said Dr. Daniel Kolansky, an interventional cardiologist and associate professor of medicine at the University of Pennsylvania's Perelman School of Medicine.

Kolansky said doctors typically monitor blood pressure during routine office visits. He offered this advice for patients when talking to their doctors: "You should say, 'What is my pressure, is it well enough controlled and is there anything further we should do?'"

Sampson said more information is needed to understand why so many people are not getting recommended blood pressure treatments.