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A landmark federal study that involved Utah patients challenges decades of thinking on blood pressure and gives a clearer picture of pluses and minuses of more aggressive treatment.

The study, released Monday, found that those who keep the top number in their blood pressure reading — systolic blood pressure — below 120 reduce their risk of heart attack, heart failure or stroke by 24 percent and overall risk of death by 27 percent.

The University of Utah was one of the five centers coordinating the work of about 100 medical centers that recruited 9,300 patients for the research.

U. kidney specialist Alfred Cheung was the principal investigator, leading 17 of the centers, including the Veterans Affairs Medical Center and Intermountain Health Care, for one part of the study. Altogether, 264 Utahns participated in the research, according to a U. spokesman.

The study was stopped in September, nearly two years early, when it became clear that lower pressure for most people older than 50 helps prevent heart problems and deaths. When the National Institutes of Health stopped the study early, the potential side effects and other key details were not disclosed.

Full results came Monday at an American Heart Association conference in Orlando and were published online by the New England Journal of Medicine, along with a dozen commentaries in three science journals.

"Overall, we deemed that the benefits far outweigh the risks" of aiming lower, said one study leader, Dr. Paul Whelton of Tulane University.

One in three U.S. adults has high blood pressure, a reading of 140 over 90 or more. Normal is under 120 over 80.

Yet the study enrolled people with a top number of 130 or more, somewhat muddying the notion of who needs treatment.

Of the more than 9,300 people enrolled, half got two medicines, on average, to get their top blood pressure reading below 140. The rest got three drugs and aimed for under 120. After one year, 1.65 percent of the lower-pressure group had suffered a major heart problem or heart-related death, compared with 2.2 percent of the others. About 3.3 percent of the lower-pressure group died, versus 4.5 percent of the others.

Too-low blood pressure, fainting episodes and, more worrisome, kidney problems were 1 percent to 2 percent higher in the lower-pressure group. Yet falls causing injury due to lightheadedness were not more common, as had been feared, especially for older people. The risks were considered well worth the benefits of a lower risk of heart trouble and death.

The study involved people older than 50. People with diabetes were excluded, so the results do not apply to them. The results also may not apply to people with previous strokes, the very old, those with severe kidney disease or people already taking a lot of different drugs, said Dr. James Stein, who heads the high-blood pressure program at the University of Wisconsin in Madison.

People who start with a high top reading, such as 170 or 200, also may not do well trying to drop too low so suddenly, Dr. Murray Esler of Baker IDI Heart and Diabetes Institute in Melbourne, Australia, wrote in a commentary in the journal "Hypertension."

The new study "makes sense and is a major advance," Stein said. "Time to fix the guidelines," which come from many groups and aim for a top number of 130 to 150, depending on age and other factors, such as whether the patient has diabetes.

"If we lower the goal ... you'll see more and more people getting to lower pressure," said Dr. Daniel Jones of the University of Mississippi, a heart association spokesman.

The Salt Lake Tribune contributed to this report.