About 37 percent of adults in the U.S. have prehypertension, or blood pressure between 120 and 139 millimeters of mercury (the systolic, or upper number) and/or 80 to 89 mmHg (the diastolic, or lower number). You’re more likely to develop this if you have other risk factors for heart disease, such as being overweight or a smoker, or if you have a family history of hypertension.

Make Sure Your Blood Pressure Reading is Correct

If your doctor tells you that you have prehypertension, make sure that you really are in the prehypertensive range by having your blood pressure checked by a medical provider at least two or three times. And take care that it’s done in optimal conditions. That means you should avoid caffeine or exercise for at least 30 minutes before your blood pressure is checked. Also, empty your bladder beforehand. Finally, ensure that you've been sitting quietly for at least 5 minutes with your back against your chair (instead of sitting on an exam table with your legs dangling), and that you keep your arm in one position.

Your doctor may also suggest that you take your blood pressure at home or have it done at a drugstore to be certain that your levels aren’t elevated because you’re nervous during an office visit.

Know How Prehypertension Can Harm You

Up to 26 percent of people with low-level prehypertension and up to 50 percent with higher-level prehypertension will develop high blood pressure within five years.

Research has also found that people with prehypertension have a greater chance of developing cardiovascular disease, especially if their blood pressure is in the higher range of prehypertension. An analysis that involved close to 1 million people found that those with prehypertension had a 36 percent higher risk of developing coronary heart disease than those without the condition. That was true even after other cardiovascular risk factors were considered.

Take Steps to Stay Healthy with Prehypertension

You probably won’t need medication if you have prehypertension. More than half of those with it are treated with drugs, but there’s no convincing evidence that they help reduce the chance of developing high blood pressure.

You can cut your risk of developing full-blown high blood pressure (and reduce the likelihood of cardiovascular disease) with lifestyle changes.

“Take a good look at what you’re eating, and get off the couch,” says Nieca Goldberg, M.D., medical director of the Joan H. Tisch Center for Women’s Health at the NYU Langone Medical Center and a spokeswoman for the American Heart Association (AHA).

The most important step is dropping some pounds if you’re overweight. According to a recent Cochrane review, losing about 9 pounds can lower systolic blood pressure in overweight, hypertensive adults by about 4.5 points.

To help even more, the AHA recommends at least 40 minutes of moderate exercise three to four times a week; consuming less than 1,500 mg of sodium per day (a little more than half a teaspoon of salt); limiting alcohol to no more than two drinks per day for men, one for women; and following the DASH diet, which is rich in fruits, vegetables, whole grains, low-fat dairy, beans, skinless poultry, and lean meat and fish.