WEDNESDAY, June 30, 2004 (HealthDayNews) -- Contradicting conventional medical wisdom, a new study finds that people with apparently normal blood levels of a hormone called aldosterone can be at increased risk of high blood pressure.
"It is a very exciting finding that has tremendous public health implications," said one expert, Dr. Bertram Pitt, a professor of medicine at the University of Michigan.
Traditionally, doctors treating high blood pressure have been concerned only about unusually high levels of aldosterone, Pitt explained. The new finding indicates that some people whose blood pressure can't be controlled with standard medications such as diuretics might benefit from an aldosterone-blocking drug, he said.
The new research is published in the July 1 issue of the New England Journal of Medicine. It comes from the long-running Framingham Heart Study, in which researchers from the National Heart, Lung, and Blood Institute have monitored thousands of New Englanders since 1948.
This part of the study linked blood levels of aldosterone to the later development of high blood pressure, which is a major risk factor for heart attack, stroke, and other cardiovascular diseases. Following 1,688 participants who started with normal blood pressure, the researchers found that the 25 percent of people with aldosterone levels at the high end of normal were 60 percent more likely to develop high blood pressure over the next four years than those with the lowest aldosterone levels.
Aldosterone is produced by the body to retain salt when it is lacking in the diet, said Dr. Daniel Levy, director of the Framingham Heart Study. Normally, aldosterone production is reduced when people eat the kind of high-salt diet common in the United States, but "some of us may not be able to regulate it in that way," Levy said.
About 90 percent of cases of hypertension -- the medical name for high blood pressure -- are classified as "essential," which simply means that there's no evident cause. Abnormally high aldosterone levels are known to cause some of the other 10 percent of cases.
"What they [study researchers] found is new, that people in the normal physiological range of aldosterone have an increased risk of hypertension," Pitt said. "There are lots of implications for the therapy of hypertension."
High blood pressure usually can be controlled with combination drug therapy using such medications as diuretics and beta blockers, but treatment does not work in some cases, Pitt said. Adding an aldosterone blocker might be appropriate for those people, he said.
Until recently, only one aldosterone-blocking drug was available, spironolactone. Doctors have been reluctant to use it because it can cause serious side effects, including nausea, vomiting, diarrhea, and breast enlargement in men.
But a newer aldosterone blocker, eplerenone, doesn't produce such side effects. Doctors can consider using it when conventional therapy fails to keep blood pressure under control, Pitt said.
Dr. William W. Frishman, chairman of the department of medicine at New York Medical College, said the finding raises the possibility of preventing high blood pressure by giving an aldosterone blocker.
"This can be a biological marker of individuals who will develop hypertension," he said. "We are always looking to know who is susceptible, and this identifies a susceptible group."
Levy added, "Clearly, more research is needed to understand the relationship of aldosterone and blood pressure," he said.
The National Library of Medicine outlines the causes, consequences, and treatment of high blood pressure.