Kim Painter

Special for USA TODAY

People with prehypertension — blood pressure above ideal levels but not high enough to be called hypertension — have a significantly increased risk of stroke, according to a new study that reinforces previous findings.

The study from Chinese researchers, published Wednesday in the journal Neurology, is a good reminder that the risks of rising blood pressure start before readings reach 140 over 90 millimeters of mercury, the point at which hypertension is diagnosed, say experts in the United States.

The 49 million Americans with prehypertension (blood pressures between 120/80 and 139/89) should pay attention to their numbers and try to reduce them — starting with controlling their weight, exercising and eating a diet low in salt and high in fruits and vegetables, the experts say.

But experts disagree about whether any of those people should take blood pressure drugs, a measure that the authors of the new study say deserves more study.

Cutting stroke risks for the 30% to 50% of adults worldwide affected by prehypertension could have "a major public health impact," study co-author Dingli Xu said in an email. Xu is a physician at Southern Medical University in Guangzhou, China.

For the study, Xu and colleagues combined data from 19 previous studies involving more than 760,000 people followed for four to 36 years.

They found that those with blood pressures in the prehypertensive range were 66% more likely to have strokes than those with ideal blood pressures, below 120/80. The risk rose as the numbers did, nearly doubling at levels above 130/85. The link showed up whether or not people had other risk factors, such as diabetes and smoking.

Other studies have found that people with full-blown hypertension have stroke risks three to seven times higher than normal, Xu says.

There's no question the stroke risks associated with all levels of elevated blood pressure are real, say two experts not associated with the study.

"Studies have showed time and time again that the higher the blood pressure, the higher your risk of some of these bad outcomes such as stroke and also heart attack, heart failure and kidney disease," says Paul James, a professor of family medicine at the University of Iowa.

"We want the public to understand that you need to do something" when blood pressure rises, even before it reaches hypertensive levels, says Ralph Sacco, a spokesman for the American Heart Association and a neurologist at the University of Miami.

"Lifestyle modification is the No. 1 recommended approach," Sacco says, and James agrees. But the two disagree on whether antihypertensive drugs have a role.

James says no. He helped write recent guidelines on blood pressure treatment that recommended against medications for certain people with prehypertension who also have diabetes or kidney disease. The guidelines, which are controversial, also recommend against treating people over age 60 with drugs unless their numbers are well in the hypertensive range, at 150/90 or above. For younger people, the guidelines say treatment should start at 140/90.

Those recommendations are based on gold-standard studies, James says. He says "no randomized, controlled clinical trials have ever been able to show benefit by giving medication" to broader groups of people.

He notes that medications to control blood pressure can have side effects that include lightheadedness, swollen feet and low potassium levels. One recent study also found an increased risk of serious falls in older adults taking the medications, he says.

But Sacco, who is critical of the guidelines, says he worries about not treating some people at particularly high risk for stroke who are unable to get their borderline blood pressure under control with lifestyle changes.

"I think it depends on the individual," he says, and on additional risk factors ranging from diabetes to family health history. It makes no sense, he says, "to say that at 140 you are hypertensive but at 139 you are not."