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A startling new report finds that almost half of all Americans — 121 million adults — have some form of heart disease, a significant increase over the last three years. While that alarming number, released Thursday by the American Heart Association, is largely due to changes in blood pressure guidelines — it is a warning about our increasingly sedentary lives, heart doctors say.

In 2017, hypertension, a major risk factor for heart disease, was redefined by the Heart Association as a blood pressure of 130/80, lowering it from 140/90. That change meant that millions more Americans, 20 to 60 and older, were now considered to have some form of heart disease.

“As one of the most common and dangerous risk factors for heart disease and stroke, this overwhelming presence of high blood pressure can’t be dismissed from the equation in our fight against cardiovascular disease,” Dr. Ivor J. Benjamin, volunteer president of the American Heart Association and director of the Cardiovascular Center at the Medical College of Wisconsin in Milwaukee, said in a statement.

Cardiovascular disease is the No. 1 cause of death in the United States, claiming more than 840,000 lives per year. After decades of steady decline, deaths rose by almost 4,000 cases from 2015 to 2016.

“It is a startling number but not an overwhelmingly surprising one given the increased prevalence of obesity, diabetes, and sedentary lifestyle,” said Dr. Jennifer Haythe, co-director of the Women’s Center for Cardiovascular Health at the New York-Presbyterian/Columbia University Medical Center. “The hope is that the numbers startle people into changing their lifestyles and that people go to the doctor to have some of their cardiovascular risk factors assessed.”

Eighty percent of all cardiovascular disease can be prevented by not smoking and controlling high blood pressure, diabetes and high cholesterol, along with regular exercise and healthy eating.

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The hope is that the numbers startle people into changing their lifestyles.

High blood pressure raises the risk for heart attacks, strokes and many other problems. Only about half of people with hypertension have it under control, according to research.

Leading cardiologist Dr. Steven Nissen cautions that the findings don't necessarily mean heart disease in the U.S. is worsening. Overall, deaths attributed to heart disease have fallen by 17.7 percent over the last several decades, largely due to declining smoking rates.

“What has happened is that the 120 million Americans cited here reflect a growing number of patients with hypertension based on a change in the blood pressure guidelines,” said Nissen, chairman of the department of cardiovascular medicine at the Cleveland Clinic. “Despite the study's claims, we have made substantial progress in the field, and coronary artery disease has decreased significantly in the past several decades.”

A diagnosis of high blood pressure doesn’t automatically mean that medication is needed or that someone actually has coronary artery disease, a common type of heart disease where the arteries that supply blood to the heart become hardened and narrowed.

“A blood pressure of 130/80 is an important reminder to employ lifestyle modifications. These are risk factors we can completely control, like diabetes, smoking and diet,” said Dr. Leslie Cho, cardiologist and director of the Cleveland Clinic's Women's Cardiovascular Center.

“If you lower your body weight you can decrease your blood pressure by about 8 [blood pressure points], and we’re not talking about hundreds of pounds here. We’re talking about as little as 5 percent of your body weight,” she added.

How to lower heart disease risk

Regular physical activity and following plant-based diets such as DASH, a meal plan that emphasizes fruits, vegetables and whole grains are shown to protect the heart.

Not all patients have the same optimal targets, but it's important to know blood pressure, glucose, and cholesterol numbers, Dr. Elizabeth Jackson, professor in cardiovascular disease at the University of Alabama at Birmingham, told NBC News via email.

Haythe believes the report's public health message is important.

“Forty-eight percent of people won't drop dead of a heart attack,” she said. “But the report does show that there is an increase in the prevalence of coronary heart disease risk and highlights the importance of managing those risks factors with lifestyle changes and appropriate treatment.”

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