MONDAY, April 25 (HealthDay News) -- Although the death rate among Americans with high blood pressure, or hypertension, has fallen since the 1970s, it still far exceeds the death rate for those with normal blood pressure, new research finds.

U.S. researchers looked at data on about 23,000 adults aged 25 to 74 from two national health surveys: the National Health and Nutrition Examination Survey (NHANES) I, which recruited participants between 1971 and 1975; and NHANES III, which enrolled adults between 1988 and 1994.

Death rates among those with high blood pressure fell between the two time periods, from 18.8 per 1,000 person-years to 14.3 per 1,000 person-years. But the death rate for people with hypertension was 42 percent higher than for those without hypertension in the earlier period and 57 percent higher than for those with healthy blood pressure in the later survey.

The study is published in the April 26 issue of Circulation.

"The whole population has been benefiting from longer life expectancy," said Dr. Earl Ford, study author and medical officer with the U.S. Public Health Service at the Centers for Disease Control and Prevention. "The drop was greater among people without hypertension than for those with hypertension."

Researchers are concerned that while death rates improved for the general population, people with high blood pressure benefited less than the rest of the population.

For example, death rates for diseases of the circulatory system fell about 46 percent for those without hypertension but only 37 percent for those with hypertension. Stroke deaths dropped 51 percent for those without hypertension and just 39 percent for those with hypertension, while deaths from heart disease declined 46 percent for those without hypertension and 35 percent for those with hypertension.

Though men with hypertension were more likely to die than women with hypertension in both time periods, men's reduction in blood pressure was more than four times greater than women's.

"For women, there was relatively little change," Ford said.

Blacks with hypertension had a higher rate of death than whites with hypertension in both time frames, although the gap narrowed a bit.

Participants were followed for an average of 17.5 years in NHANES I and 14.2 years in NHANES III.

The data also showed other differences between those with hypertension and those without. Although cholesterol levels fell for the general population, those with hypertension had a 45 percent smaller reduction.

Body mass index, a measurement of height and weight used to identify obesity, increased overall, but slightly more among those with hypertension.

People with hypertension also were more likely over the years to develop diabetes. About 5.9 percent of those with hypertension in the 1970s had diabetes; by the 1990s, that figure rose to 11.4 percent.

Among people with normal blood pressure, diabetes incidence rose from 2 percent to 3.5 percent.

On the positive side, smoking rates fell in the general population since the 1970s, and even more so among those with hypertension.

Dr. Donald LaVan, American Heart Association spokesman and clinical associate professor of medicine at University of Pennsylvania, noted that the definition of high blood pressure has changed over the years. In the 1970s, he said, 160/95 mm Hg was considered high blood pressure, while 140/95 was the threshold in the 1980s, and today, 130/90 is considered elevated.

High blood pressure can raise the risk of heart disease and stroke, and doctors today better understand the importance of treating it, he added.

Though the data did not track if or how people were treated for high blood pressure, better treatment is likely one reason for the decline in death rates, LaVan suggested.

Today, in addition to the diuretics and beta blockers that were used in the 1970s, doctors can prescribe ACE-inhibitors and angiotensin II receptor blockers to treat high blood pressure, he said.

"The bottom line on this is, don't fool around with high blood pressure," LaVan said. "You've got to get your weight under control. Restrict sodium intake. Exercise. And you've got to take your medicine. It actually pays off. There is no question about it."

About 29 percent of adults in the United States had hypertension in 2007-2008, a figure little changed from the 1980s, according to background information in the study.

More information

The American Heart Association has more on high blood pressure.