Many people who have dutifully given up soy sauce, pickles and pretzels in an attempt to prevent high blood pressure by limiting salt may be sacrificing needlessly, a growing number of researchers now believe.
For about half of those with hypertension, they say, restricting salt has little effect; for many of the others, the benefits are slim.
And just as salt, or sodium, has been downgraded as a culprit in the genesis of high blood pressure, other dietary suspects are gaining ground: Recent studies suggest that for a number of people it is not too much salt, but too little calcium, that sets the stage for hypertension.
Although still controversial, this "calcium connection" has already led some blood pressure specialists to advise patients that they may eat pretzels at least in moderation, as long as they drink milk too. "We have signals from many different sources telling us that maybe it is calcium and not sodium that is the problem," said Dr. David McCarron of the Oregon Health Sciences University in Portland.
Experts are increasingly divided about the relative importance of these two minerals in hypertension, and patients may receive conflicting advice.
Although most doctors still see sodium as the main culprit, their conviction is not nearly so strong as it once was.
"People have been interested in the salt question for 50 years, and there's still no compelling evidence one way or another," said Dr. William Harlan head of disease prevention at the National Heart, Lung and Blood Institute. "To me that says we've expected too much from salt and the size of the effect must be small.
"I do think there's a problem when we focus on sodium without looking at the other ions in the diet, like calcium and potassium," he added. "I think they are related in a way we don't understand."
Although the Joint National Committee on High Blood Pressure, a federal advisory body, still recommends salt reduction for all people with hypertension, many experts no longer support a blanket practice. They are perturbed that the public views salt as a hazard to be avoided by people who are healthy.
"There is no evidence that salt can cause hypertension in people with normal blood pressure," said Dr. Thomas Ferris, head of the department of medicine at the University of Minnesota Medical School. "This business of taking salt out of baby food is just silly, and it bugs me that I sometimes can't get salted pretzels because of this irrational fear."
Experts in the revisionist camp say that the original studies linking a low-salt diet and lowered blood pressure involved extreme salt deprivation that is not practical in the Western world and that attempts to lower high blood pressure with realistic low-salt diets have been disappointing.
Most Americans consume 4 to 5 grams of sodium a day and can reduce that level to 2 grams by avoiding naturally salty foods and adding no salt in cooking or to meals.
At the same time, tantalizing new studies have suggested that an inadequate intake of other dietary minerals, particularly calcium, may be at least as important as sodium in producing hypertension. Among the new findings are these:
* In a study of 60,000 nurses followed by Harvard researchers, those whose diet was very low in calcium and magnesium had a 23 percent greater chance of developing high blood pressure over a four-year period.
* In research by McCarron, people with mild hypertension cut their blood pressure to normal levels when taking calcium supplements; levels jumped again when the pills were stopped. But other studies have not reliably produced the effect.
* A group of black people with low dietary calcium intake and high blood pressure reduced their blood pressure significantly using calcium supplements, according to researchers at Wayne State University in Detroit. Some experts believe the very low calcium content of the average African-American diet may be the key to the mysteriously high rates of hypertension in that group.