Salt: the pressure is on.

It was the kind of language you don't expect from a prestigious medical journal.

On May 18, the British Medical Journal (BMJ) published an analysis of a landmark study on salt and blood pressure.(1) The analysis was written by Richard Hanneman, president of the Salt Institute, a trade association of U.S. salt producers.

"We publish this analysis not because we believe it," explained an editorial note that accompanied Hanneman's article, "but so as to present readers with an example of how the salt industry works."

Ironically, less than a week after the BMJ ran the salt industry's analysis (along with two stinging commentaries), the equally respected Journal of the American Medical Association (JAMA) published a study "purporting to show that a high-salt diet may do you no harm," noted the BMJ.(1) "Is this a coincidence?" it asked.

One look at the sponsor of the JAMA study--Campbell Soup Company's Institute for Research & Technology--suggests that it was anything but.

A high-salt diet raises blood pressure, according to the nation's leading health authorities. Clearly, a few scientists disagree. But it's not just the usual back-and-forth of scientific debate that propels salt into the news so often.

"Faced with a growing scientific consensus that salt increases blood pressure, and the fact that most dietary salt (65 to 85 percent) comes from processed foods," said the BMJ in its editorial, "some of the world's major food manufacturers have adopted desperate measures to try to stop governments from recommending salt reduction."

"Rather than reformulate their products, manufacturers have lobbied governments, refused to cooperate with expert working parties, encouraged misinformation campaigns, and tried to discredit the evidence."

Here's a brief look at that evidence...and a glimpse of the industry's efforts to undermine it.

THE BIG PICTURE

Who says we should eat less salt?

The National Institutes of Health's High Blood Pressure Education Program, the U.S. Surgeon General, the National Academy of Sciences' National Research Council, the World Health Organization's Expert Committees on the Prevention of Coronary Heart Disease, and the 1995 Dietary Guidelines for Americans, for starters.

Their advice is based not on the latest study to hit the news, but on hundreds of studies on animals, people, and large populations.

"A cornerstone of biomedical science is that the totality of research--from all investigative methods--must be considered in order to arrive at sound judgment as to cause-and-effect," explains Jeremiah Stamler, a world renowned expert on heart disease and professor emeritus at Northwestern University Medical School in Chicago. "The Salt Institute omits any mention of this massive literature."

* Animals: Salt Causes High Blood Pressure. Rats, dogs, chickens, and rabbits. Over the last half century, studies have shown that salt raises blood pressure in each of those species.

But none rivals a long-term study on chimps published last year by researchers at the University of Melbourne and elsewhere.(2)

"Chimps are the closest to man we'll ever get to study," says Norman Kaplan, a hypertension expert at the University of Texas Southwestern Medical Center in Dallas.

Half of the chimps got their usual low-salt diet of fruits and vegetables. The other half got the same diet plus enough salt to supply 2,000 mg of sodium a day, 4,000 mg a day, and finally 6,000 mg a day before they were switched back to the low-salt fare.

"Adding 2,000 milligrams a day raised the chimps' systolic blood pressure by 12 points," says Kaplan. At 6,000 mg a day, blood pressure was up 26 points. (Systolic pressure is the higher number; diastolic is the lower.)

That's not all. "Taking the salt away lowered their blood pressure to its original level," says Kaplan. "That one set of data is about as conclusive as one would ever expect to get."

* Populations: Higher Salt Means Higher Pressures. If salt raises blood pressure, wouldn't populations that consume more salt have higher pressures than comparable populations that consume less? And wouldn't the people within each population who eat more salt have higher pressures than the people who eat less?

Numerous studies have found just that.(3) But the granddaddy of the so-called "observational" studies, called INTERSALT, has gotten more attention than all the others combined.

The strategy behind INTERSALT was simple: A team of investigators studied more than 10,000 men and women aged 20 to 59 living in 52 populations in 32 countries. Among other things, the researchers measured blood pressures and the amount of sodium excreted over 24 hours. (How much sodium you excrete is the best gauge of how much you consume.)

The results, first published in 1988, confirmed the link between salt and blood pressure.(4)

"In individuals and in whole populations," says Stamler, "higher-salt intake is a major factor--independent of too little potassium, too much alcohol, and excess body weight--that's significantly related to higher blood pressure."

Last May, the INTERSALT team published an update of its 1988 findings.(1) "The more recent and more sophisticated analysis demonstrates a larger effect than we previously found," says Stamler.

How large? A person who ate an extra 2,300 mg of sodium a day had a systolic blood pressure three to six points higher than a person who ate no extra sodium. "And even that's an underestimate," says Stamler.

What's more, INTERSALT showed that salt exaggerates the rise in blood pressure that occurs as people age. An extra 2,300 mg of sodium a day meant that the difference in systolic blood pressure between ages 25 and 55 would be an extra 10 points greater than it would otherwise be. That's no small potatoes.

"It means a 34 percent higher risk of dying of stroke and a 21 percent higher risk of dying of heart disease," explains epidemiologist Malcolm Law of the Royal London School of Medicine. "Excess dietary salt is a serious public health hazard."

But despite the massive evidence, the salt industry has argued that INTERSALT proves that salt is harmless. In the May 18 British Medical Journal, the Salt Institute's Richard Hanneman published an analysis of INTERSALT that Malcolm Law described as "bizarre."(1)

Alan Dyer, an INTERSALT investigator at Northwestern University Medical School, was equally blunt. "Hanneman's criticisms are based on flawed analyses."

* Clinical Trials: Cutting Salt Lowers Blood Pressure. It's one thing to just measure--or "observe"--blood pressures in populations or people who eat high- vs. low-salt diets. It's another to put people on a lower-salt diet and see if their blood pressures fall.

Researchers have conducted dozens of those studies, called clinical trials.(3,5,6) "There's no question that salt influences blood pressure. That's absolutely certain," says Richard Grimm, a researcher at the Shapiro Center for Evidence-Based Medicine at the University of Minnesota in Minneapolis.

So why did JAMA send out a press release with its don't-worry-about-salt study, and why did it carry this attention-grabbing headline: "Reducing Salt in Diet has Little Effect on Blood Pressure"?

And why did its press release fail to mention that Claude Lenfant, who is the director of the National Heart, Lung and Blood Institute (NHLBI), had written an accompanying editorial that criticized the study? Maybe the journal was hungry for headlines.

The study--which was co-authored by Alexander Logan and colleagues at the University of Toronto--was a meta-analysis, which pools data from already-published, smaller studies. Logan's conclusion: Cutting sodium lowers blood pressure in people with high, but not normal, blood pressure.

Nice headline. Wrong conclusion. In fact, the meta-analysis found that cutting salt lowered systolic pressure significantly in people with normal blood pressure.

"That's in accordance with other data on salt and blood pressure," says Stamler. "But the report is so biased, you'd never know it."

Here's why:

*One-Sided Results. Of the 56 trials Logan examined, 28 were on people with normal blood pressure. But he based his sweeping conclusion--that salt doesn't matter--on just 14 of those trials...ones in which people were not fed all of their meals in a medical school or other research institution.

Yet most researchers prefer to rely on studies of people whose diets are carefully controlled by researchers.

"Whenever people are eating at home, cafeterias, or restaurants," says Stamler, "you have to ask: `Are they sticking to the recommended sodium intakes or do you have an adherence problem?' Logan never discusses adherence."

In fact, he notes, when Logan looked at all the trials on people with normal blood pressure, the drop in systolic blood pressure was statistically significant.

"And if Logan had analyzed only the 14 trials where people were fed in institutions--where adherence was probably better--the drop would have been even greater," says Stamler. "Instead, he ignores them."

* Too-Short Trials. "The results of a meta-analysis are only as good as the studies you decide to exclude or include," explains Grimm.

Four of the 56 studies that Logan included in his meta-analysis were done on children, whose lower blood pressures don't change as much as adult pressures. Another 18 lasted less than two weeks. "You'd expect it to take at least a month to get the full effect of sodium reduction," explains Jeffrey Cutler, an NHLBI epidemiologist.

It didn't take Hanneman long to answer the criticism. "The shortterm trials had the strongest impacts of blood pressure lowering due to salt restriction," he said in a press release.

"That's what they claim," says Stamler. "But nowhere in the paper are there any data to show that the longer trials had the weakest impact."

In fact, most researchers don't even consider small, short-term studies now that there are large, long-term ones like the Trials of Hypertension Prevention (TOHP), which studied 2,000 people with normal blood pressure for roughly three years.(5)

"I put a lot more weight on the large, rigorous trials like TOHP than on the short studies that may not have even achieved a sodium reduction," says Paul Whelton, director of the Welch Center for Prevention, Epidemiology, and Clinical Research at The Johns Hopkins Medical Institutions in Baltimore.

"The big ticket message from the carefully conducted trials is that when you lower sodium, you get a corresponding drop in blood pressure," he adds. Another meta-analysis--one that didn't include the shortest studies--reached the same conclusion.(7)

DIET VS. DRUGS

The food and salt industries' influence isn't the only force that's kept the salt "controversy" afloat. Many physicians are reluctant to advise their patients to eat lower-salt diets, especially if they don't yet have high blood pressure.

"If the whole population were eating about 2,300 mg of sodium a day instead of close to 4,000 ma, the average blood pressure would drop about two or three points," explains the University of Minnesota's Richard Grimm. "And we know that that's an underestimate, because sodium in the diet is hard to measure.

"That would shift the whole distribution of blood pressures down, would shift a lot of people out of the `hypertensive' range, and would prevent disease," he explains

But changing lifestyles isn't quick and easy. "Getting people to cut salt, lose weight, eat more fruits and vegetables, and limit alcohol takes time and energy," says Kaplan. "You can't just give people a diet list. You've got to motivate them and keep at it."

The same holds for people who already have high blood pressure. "Many physicians say: `Why bother cutting salt when I can give my patients a drug and their blood pressure will go down 10 points?'" says Grimm.

In fact, there can be a big payoff. "In the Treatment of Mild Hypertension Study (TOMHS)," says Grimm, "among people who cut back on salt, increased activity, and cut back on alcohol, blood pressures went down ten percent.(8) That's about what you can expect from a drug."

The fact is, avoiding high-salt foods does take effort...but it shouldn't have to. "The only way to make a major shift is for the food industry to get some of the salt out of processed foods," says INTERSALT investigator Alan Dyer.

But that hasn't been easy.

"The industry seems to want it to appear that there's no consensus so that people don't have to worry about salt," he adds.

Keep that in mind when you see the next headline on the "salt controversy."

RELATED ARTICLE: Six Reasons To Eat Less Salt

Your blood pressure is "normal." So why bother cutting salt? Here are six good reasons.

1. Just because you don't have high blood pressure, it doesn't mean you won't. "Only" two out of ten people in their 40s have blood pressure that's high enough to treat with drugs. But your odds jump to five out of ten in your 60s, and six out of ten after that (see "Older & Higher").

2. Even so-called "normal" blood pressure increases the risk of heart attack and stroke. Most Americans have "normal" or "high-normal" pressure (see "Normal Isn't Optimal"). Their blood pressures aren't high enough to consider treatment with drugs, but anything over "optimal" (less than 120 over less than 80) raises the risk of heart attack and stroke.

"The higher your blood pressure, the higher your risk," says the University of Minnesota's Richard Grimm.

3. Don't assume that you're not "sensitive" to salt. The Salt Institute claims that only a small fraction of Americans are salt-sensitive. Don't believe it.

"Most reports on salt sensitivity have serious limitations," says Northwestern University Medical School's Jeremiah Stamler. "From population studies like INTERSALT and other evidence, we can infer that salt-sensitivity is common." What's more, he adds, "there's no simple test to see if you are salt-sensitive," so people should assume that they are.

4. Drugs have side effects. Blood-pressure-lowering drugs--though necessary for some people--cost money and can cause side effects like impotence, chronic cough, and fatigue. If you ever do need drugs, cutting salt and other lifestyle changes can lower the dose.

5. Cutting salt is safe. Forget what you've heard about the "dangers" of lower-salt diets (courtesy of the Salt Institute).

For example, some short-term experiments using extremely low-salt diets report that cutting salt raises cholesterol levels. "With a very low sodium intake of about 200 mg a day, blood volume shrinks, so it makes the concentration of cholesterol higher," explains hypertension expert Norman Kaplan. "That's temporary, and it doesn't happen with ordinary lower-salt diets."

Other flawed low-salt scares: A well-publicized--but severely limited--1995 study reported a higher risk of heart disease among men who were taking blood-pressure-lowering drugs and who were consuming less than 2,000 mg of sodium a day.(1) But the researchers failed to report how many calories the men ate and how often they smoked and drank alcohol.

"It's possible that the men who consumed the least sodium were heavy drinkers," says Jeffrey Cutler of the National Heart, Lung and Blood Institute. "And people who are heavy drinkers are also heavier smokers. Everyone knows how much smoking contributes to higher risks of heart attack."

6. Salt causes more than hypertension. A growing body of evidence indicates that salt increases calcium excretion, which raises the risk of osteoporosis and kidney stones. That's not all. "Though it's not as strong as it is for hypertension, there is evidence that salt increases the risk of asthma, stomach cancer, and heart enlargement," says Stamler.

(1) Hypertension 25: 1144, 1153, 1995.

RELATED ARTICLE: THE BOTTOM LINE

To keep your blood pressure optimal as you age:(1)

* Limit sodium to no more than 2,400 mg-and preferably 1,800 mg-a day. High-sodium foods don't always taste salty. Check labels for the lowest-sodium brands. Avoid foods with more than 480 mg of sodium per serving. That's 20 percent of the Daily Value.

* Lose excess weight. As few as ten pounds can make a difference.

* Walk briskly, jog, swim, cycle, or do other aerobic exercise for 30 to 45 minutes at least three times a week.

* Limit alcohol to no more than two drinks a day. Women should stop at one a day to cut their risk of breast cancer.

* Get more potassium, magnesium, and other nutrients by eating five to nine servings of fruits and vegetables a day.

For infants and children:

* Cut excess salt. In a Dutch study, newborns who were fed--in addition to breast milk--formula and foods providing 22 mg of sodium a day had lower blood pressures than those fed diets with 58 mg a day. What's more, the difference in blood pressure was still there 15 years after the study ended.(2)

(1) Archives of Internal Medicine 153: 186,1993.

(2) Journal of Hypertension 14 (suppl.) S210, 1996.

(1) British Medical Journal 312: 1239 1240,1241,1249,1283,1287,1996.

(2) Nature Medicine 1: 994, 1009 1995.

(3) British Medical Journal 302: 811, 815, 819, 1991.

(4) British Medical Journal 297: 319, 1988.

(5) Journal of the American Medical Association 267: 1213, 1992.

(6) Hypertension 17 (suppl. 1): 1-21, 1991.

(7) Hypertension 17 (suppl 1): 1-27, 1991.

(8) Archives of Internal Medicine 151: 1413, 1991.