BOSTON (CBS) – For the first time in more than a decade, the American Heart Association is changing the guidelines for high blood pressure. This means nearly half the US adult population is living with hypertension and at an increased risk of heart disease and stroke.

Charles Cronenweth has been working to lower his blood pressure for the last 10 years. Tens of millions more Americans will soon be learning they also have hypertension.

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The American Heart Association and American College of Cardiology are now defining a top reading of 130 or more or a bottom reading of 80 or more as high blood pressure. The old definition of high was 140 over 90.

“Most of them just need to know they are at high risk, but they can manage that problem on their own,” says Dr. Paul Whelton who co-authored the new guidelines. “They are empowered to improve their lifestyle,” he adds.

This change is expected to have the biggest impact on men and women who are under the age of 45.

New Blood Pressure Guideline (American Heart Association/ American College of Cardiology)

“They would have to exercise more, have a better diet, a diet that is low in sodium, restrict alcohol and lower stress,” says Dr. Ravi Dave of UCLA Health.

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Under the new guidelines, 120 or less is still normal blood pressure, but up to 129 is considered elevated and at 130 begin different stages of high blood pressure and an increased risk of heart attack and stroke.

Even though 14 percent more people will be diagnosed with high blood pressure, only a small portion will take home prescriptions.

“Preventing getting hypertension is much better than treating hypertension,” explains Dr. Whelton. “It’s good to treat it when it’s there, but it is way better to prevent it.”

Cronenweth agrees, saying, “I try to eat a heart-healthy diet and exercise three or four times a week.” Cronenweth says he checks his blood pressure every day, and now more Americans will be getting instructions on how to do just that.

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The new guidelines also emphasize making sure blood pressure readings are accurate. The authors say blood pressure levels should be based on two or three readings at least two different times and that people should learn the proper techniques for checking their blood pressure at home.

Dr. Mallika Marshall