Yes, No . . . or Low?
From the dim beginnings of the human race, people have craved salt.
Early hominids sought out salt licks to satisfy their needs. The first agriculturists put it in their bread. As cities and towns began to develop, men established the first trading routes in order to put salt on their tables.
In some countries, salt was traded ounce for ounce for gold. The Chinese made coins out of salt, and the Romans paid their soldiers a salarium, or payment in salt, that is the precursor of the modern salary.
Today, however, salt is viewed a bit differently--at least by health authorities. Although humans still crave it avidly and food processors use it routinely to enhance flavor, most major medical groups urge us to remove it from our tables and our kitchens.
Salt, they say, is a leading cause of high blood pressure, and this hypertension, in turn, is a major cause of heart attacks, strokes and death. To combat its foul effects, they say, virtually everyone should put the saltcellar down. Bland is beautiful.
But hold on, a vocal minority of researchers insist. While it is clear that salt is linked to hypertension in some individuals, they say, the vast majority of people are either unaffected by it or can control hypertension by simply eating a healthier diet. And in some cases, low salt consumption might even be dangerous.
Asking everyone to cut back on salt to reduce the risk for a few, they argue, is like using a blunderbuss to kill a fly.
“The issue is not blood pressure,” says Dr. Michael H. Alderman of the Albert Einstein College of Medicine in New York City, president of the American Society of Hypertension. “The issue is life, heart attacks and strokes. There is no evidence that [lowering salt intake] will extend life or make it better in any way. Absent that evidence, we are not justified in asking 250 million Americans to change their diet.”
“For 20 years, we have not told people what they need to hear, which is that the best way to control blood pressure is to control weight, drink alcohol only in moderation and exercise,” says Dr. David A. McCarron of Oregon Health Sciences University. “If I had to make a list [of health factors], sodium chloride [reduction] would not make the top 10.”
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Others, of course, disagree. “We have the massive accumulation of 50 years of data on the relationship between salt intake and blood pressure, and the havoc that higher average blood pressure wreaks in the United States,” says Dr. Jeffrey Cutler of the National Heart, Lung and Blood Institute. “I don’t think we can say with a great degree of certainty what the optimally low sodium intake should be, but we can say that the vast majority of people eat far too much salt.”
“This is an issue where the scientific community is really, honestly divided,” adds Rodman D. Starke, senior vice president for scientific affairs at the American Heart Assn.
High blood pressure in an adult is defined as greater than or equal to 140/90, where 140 millimeters of mercury (mm Hg) is the systolic pressure (when the heart is beating) and 90 mm Hg is the diastolic pressure (the pressure between beats). One in every four adult Americans, about 50 million, has high blood pressure, but an estimated 35% of those don’t know it.
According to the heart association, high blood pressure kills about 38,000 Americans each year and contributes to the deaths of more than 180,000. But of all those 50 million with high blood pressure, only 21% receive adequate therapy. Another 27% receive inadequate therapy, while 52% receive no therapy at all.
There is no question that a link exists between salt and hypertension, says Dr. Myron H. Weinberger of the Indiana University School of Medicine. His studies, like those of others, have shown that about 60% of hypertensives are sensitive to salt--that is, their blood pressure rises when they consume more salt and it falls when they consume less. The study showed that 73% of African American hypertensives are salt-sensitive as are about half of white hypertensives.
In the population with normal blood pressure, about 25% are sensitive to salt, and most of those are older than 60. In both of these groups, says Dr. Suzanne Oparil of the University of Alabama at Birmingham School of Medicine, “the problem is we don’t know who these people are.”
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The average American consumes about 12 grams--about two teaspoons--of salt every day, about twice the amount recommended by such authorities as the National Institutes of Health and the heart association.
Only about a quarter of that 12 grams originates in the salt shaker at home. The rest comes from processed foods--everything from soup to nuts. It is the presence of salt in so much purchased food that makes it difficult to drastically reduce consumption.
Researchers have been studying the links between salt and hypertension for more than 50 years, but many of the studies have been too small to be convincing. The best evidence against salt was provided by an international study called InterSalt, which surveyed 10,074 men and women in 32 countries.
The study included four remote tribes in Brazil, Kenya and New Guinea. These populations had the lowest salt intake, the lowest blood pressures and virtually no hypertension.
The remainder of the population showed a weak but statistically significant link between salt consumption and blood pressure, the original authors reported in 1988.
Two years ago, a team led by Dr. Paul Elliott of the Imperial College School of Medicine in London reanalyzed the InterSalt data. They concluded that there is a link between salt intake and blood pressure at all ages, but that it is strongest among the middle-aged.
Middle-aged individuals who consumed an extra six grams of salt beyond the recommended amount per day had systolic blood pressures (which are generally most predictive of heart problems) that averaged five to seven mm Hg higher than pressures in people who consumed less salt.
At about the same time, however, Dr. Alexander G. Logan and his colleagues at the University of Toronto compiled the results from 56 separate studies that included 3,505 volunteers and concluded that low-salt diets had no effect on people with normal blood pressures. Among those with hypertension, such diets lowered systolic pressures by an average of 3.7 mm Hg.
Critics carped that Logan’s group had been highly selective in choosing studies and that the study was supported by the Campbell Soup Co., which has a vested interest in continued use of salt.
Last month, however, Danish researchers with no connections to the food industry released a similar analysis of 58 trials on hypertensive subjects and 56 more on people with normal blood pressure.
They concluded that, for hypertensive patients, salt reduction produced a 3.9-mm Hg drop in systolic blood pressure and a 1.9-mm Hg drop in diastolic pressure. In people with normal blood pressure, salt reduction produced a negligible 1.2-mm Hg drop in systolic pressure and a 0.26-mm drop in diastolic pressure.
“These results,” they concluded, “do not support a general recommendation to reduce sodium intake.”
Some researchers, such as Alderman, go beyond that position and argue that reducing salt in the diet can actually be dangerous.
Alderman reported in March on an analysis of data collected from 1971 to 1975 in the first National Health and Nutrition Examination Survey (NHANES I). A total of 11,346 Americans ages 25 to 75 were given medical examinations and asked to provide details of their food intake during the previous 24 hours.
Beginning in 1992, Alderman and his team began tracking down the original participants in NHANES I. They found that 3,293 people had died, 1,970 of them from heart disease.
Alderman divided the group of deceased participants into quartiles based on their salt intake. Controlling for a variety of other factors, such as blood pressure, cholesterol levels, age, gender and economic status, he found that those with the lowest salt consumption were the most likely to have died.
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There were 19 deaths for every 1,000 years of life among those in the highest quartile of salt consumption, compared to 23 deaths per 1,000 years in those with the lowest intake.
“The lower the sodium, the worse off you are,” Alderman says. “There’s an association. Is it the cause? I don’t know. But any way you slice it, that is not an argument for eating a low-sodium diet.”
Critics say the study should be taken with a grain of salt. The salt intakes used in the study were based only on a 24-hour sample, says Dr. Edward Roccella of the the National Heart, Lung and Blood Institute, and subjects may have misremembered or underestimated the amount of salt they were eating. And those who were eating the least salt, he charges, may have been doing so under doctor’s orders because they were already sick.
But Alderman notes that the results support an earlier study he conducted. He and his team studied 3,067 patients enrolled in a union-sponsored study of hypertension treatment. The researchers measured the salt intake of each of the participants, then tracked them for four years, including those who had died, Alderman says.
They reported in 1995 that the men who consumed the least salt were the most likely to have died from a heart attack. There were not enough deaths among the women to reach any conclusions. Alderman cautions that most of the subjects were also receiving anti-hypertension drugs.
He suggests a potential mechanism that could explain the finding. Cutting back on salt, several studies have shown, prompts the kidneys to increase production of renin, a powerful hormone that constricts blood vessels. It also swells the cells that line small arteries, including those in the heart, leading Alderman to speculate that higher concentrations could increase the likelihood of a heart attack.
It is likely to be many years--if ever--before the two sides in the debate can reach an accommodation. In the meantime, there are many things that people concerned about their blood pressure can do for themselves.
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The most important is a change in diet--not necessarily to a low-salt diet, but to a diet high in fruits, vegetables and dairy products, all of which contain the minerals calcium, potassium and magnesium.
“If you have enough of these other minerals, staying on a normal salt diet actually gives you the lowest blood pressure,” says Oregon’s McCarron.
McCarron was the lead investigator of a trial involving nearly 500 participants called Dietary Approaches to Stop Hypertension, or DASH, funded by the National Heart, Lung and Blood Institute. The DASH diet is low in fat and includes two to three servings of low-fat or fat-free milk and dairy products and eight to 10 servings of fruit and vegetables each day.
Everyone who stuck to the DASH diet reported some decrease in blood pressure, as well as weight loss, the researchers reported last year. In people with mild hypertension, the drop in blood pressure averaged 11 mm Hg systolic and 5 mm Hg diastolic, about the same magnitude observed with drug treatment.
Similar results were reported in March in a study of nearly 1,000 older people with hypertension, the Trial of Nonpharmacological Interventions in the Elderly. Using a diet similar to that in the DASH trial, the researchers found that 36% to 53% of subjects were able to stop taking anti-hypertension drugs.
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The calcium in milk and milk products was particularly important in both studies, McCarron says. Many blood pressure drugs, in fact, work by helping the body retain calcium in the diet, but getting extra quantities in the diet is better, most experts argue.
“It’s amazing how many adults do not consume calcium-containing products [like milk],” Logan says. “The only thing they will eat is cheese, and a lot of that is very high in fat. . . . I also tell my patients not to take calcium tablets as a substitute. Whenever we focus on a single nutrient and give it as a pill, we don’t see much of an effect. t’s the nutritional package, what travels with these elements, that is important.”
And such diets have many other benefits as well. Not only do they help prevent heart attacks and strokes, says Dr. Paul Whelton of the Tulane University School of Public Health and Tropical Medicine, but “we would also anticipate a reduction in the likelihood of diabetes, arthritis, breast cancer and osteoporosis.”
(BEGIN TEXT OF INFOBOX / INFOGRAPHIC)
Where the Sodium Is
FOOD: MILLIGRAMS
Apple (1): 2
Applesauce ( 1/2 cup): 10
Apple pie ( 1/8 frozen): 208
Bread (1 slice, white): 120
Pound cake (1 slice): 171
English muffin (1): 293
Butter (1 tablespoon, unsalted): 2
Butter (1 tablespoon, salted): 90
Margarine (1 tablespoon): 110
Chicken ( 1/2 breast): 69
Chicken pie (frozen): 880
Chicken dinner
(fast food): 2,243
Corn (1 ear): 1
Corn flakes (1 cup): 305
Canned corn ( 1/2 cup): 285
Cucumber (7 slices): 2
Cucumber (with salad
dressing): 234
Dill pickle (1): 310
Grapes (10 seedless): 1
Grape jelly (1 tablespoon): 3
White wine (4 ounces,
domestic): 19
Lemon (1): 1
Soy sauce (1 tablespoon): 1,190
Salt (1 teaspoon): 1,500
Milk (1 cup): 122
Dry Milk ( 1/2 cup): 322
Cottage Cheese
(4 ounces): 390
Pork (3 ounces): 59
Bacon (2 slices): 225
Ham (3 ounces): 950
Potato (1): 5
Potato chips (1 ounce): 113
Instant mashed potatoes
(1 cup): 485
Steak (3 ounces): 55
Jumbo burger
(fast food): 990
Meatloaf
(frozen dinner): 910
Tomato (1): 14
Tomato soup (1 cup): 700
Tomato sauce ( 1/4 cup): 325
Tuna (3 ounces): 50
Canned tuna (2 ounces): 250
Tuna pot pie (frozen): 715
Water (8 ounces, tap): 12
Club soda (8 ounces): 85
Antacid in water: 564
Source: The Salt Institute
