However, the study also had some good news for Americans: The risk of developing severe degrees of high blood pressure has decreased in the past 25 years, due partly to improved treatment.

The study, based on data from NHLBI's landmark Framingham Heart Study (FHS), appears in the February 27, 2002, issue of the Journal of the American Medical Association. The National Institute of Neurological Disorders and Stroke also contributed support to the research.

"Ninety percent is a staggering statistic and cause for concern," said Health and Human Services Secretary Tommy G. Thompson. "This finding should energize Americans to take steps to protect themselves against high blood pressure. By adopting some simple healthy behaviors, most people can reduce their risk of high blood pressure. Prevention gives people the power to protect their health."

"Americans have to better understand their risk of developing high blood pressure," agreed NHLBI Director Dr. Claude Lenfant. "They cannot adopt a wait and see approach. If they do, chances are they will find themselves with high blood pressure and that puts them at increased risk for heart disease and stroke.

"Fortunately," Lenfant continued, "high blood pressure is easily diagnosed and can be prevented by adopting certain lifestyle measures — don't smoke, follow a healthy eating plan that includes foods lower in salt and sodium, maintain a healthy weight, be physically active, and if you drink alcoholic beverages, do so in moderation. For those who already have high blood pressure, it's important that they properly control it with these lifestyle measures and medication."

High blood pressure, or hypertension, is a measure of the force of blood within blood vessels. It is recorded as two numbers — the systolic (the force of the blood as the heart beats) over the diastolic (the force of the blood as the heart relaxes between beats). If either or both are high — 140/90 mm Hg or above-then that is hypertension.

"Lifetime risk" estimates the chance that someone at a given age will develop a particular disease during his or her remaining years of life.

FHS began in 1948 with 5,209 participants who were aged 28 to 62 and without cardiovascular disease. Participants underwent medical examinations every 2 years.

The current study includes 1,298 of the original participants-those who had not developed hypertension by 1975. Researchers calculated lifetime risk for two ages — 55 and 65.

Additionally, the researchers compared lifetime risk from two time periods — 1952-75 and 1976-98. They examined the results to see if any trends emerged in participants' risk for developing hypertension.

Calculations were based on the current U.S. life expectancies for 55- and 65-year-olds, which are 80 and 85 years, respectively.

"We chose to calculate estimates for ages 55 and 65 because that's when the risk of developing hypertension dramatically increases," said Dr. Ramachandran Vasan, Associate Professor of Medicine at Boston University School of Medicine and a coauthor of the study.

The investigators found that the lifetime risk of developing hypertension was about 90 percent for men and women at both ages. Further, more than half of the participants aged 55 and about two-thirds of those aged 65 went on to develop hypertension within 10 years.

Both men and women had a nearly 60 percent chance of being prescribed blood pressure-lowering drugs.

Other study results include:

• Nearly 85 percent of the participants developed Stage I or greater hypertension over 20-25 years. Thirty-five to 44 percent of them went on to develop Stage II or greater hypertension.

• For women, there were no differences in lifetime risk between the earlier and later time periods. By contrast, men had a higher lifetime risk of developing hypertension during the later time period.

• Both men and women had a greater lifetime risk of receiving a hypertension medication in the more recent time period.

• The risk of developing Stage II or greater hypertension (160/100 mm Hg or higher) decreased for both men and women in the more recent time period.

"The trends over time may be due in part to an increase in obesity among the men in the study," said Vasan. "Their average body mass index rose between the two periods. Women in the study did not have such a rise in body mass index."

He added that, "The decrease in the lifetime risk of developing Stage II or greater hypertension for both men and women probably resulted from an increased use of hypertension lowering drugs through the years."

Vasan cautions that the study was not ethnically diverse. He stresses that the lifetime risk of developing hypertension varies among individuals and depends on the presence of risk factors.

"Americans should see their doctor and have their blood pressure checked," Vasan said. "They can talk about their risk factors and the steps they can take to reduce their risk of hypertension. Americans don't necessarily have to develop high blood pressure as they get older. What they have to do is take preventive action."

To interview a scientist about this study, contact the NHLBI Communications Office at (301) 496-4236.

NHLBI press releases, information on the DASH Diet, cardiovascular disease, and an interactive Web page, "Your Guide To Lowering High Blood Pressure," can be found online at www.nhlbi.nih.gov.