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Salt and high blood pressure: New concerns raised
Ah, salt. It gives personality to chips, balance to bread and flavor to just about everything else that comes in a can, jar or squeeze bottle. Salt is such a mealtime staple it can be hard to imagine life without a shaker on the table. But as far back as the 1960s, physicians linked salt to high blood pressure, a major risk factor for heart disease and stroke.
Today, more than 65 million Americans have hypertension - repeatedly high blood pressure - according to the National Heart, Lung, and Blood Institute, and 59 million more have pre-hypertension, a level higher than normal that can also lead to health problems.
For decades, the American Medical Assn., American Heart Assn., American Public Health Assn., the Institute of Medicine, the World Health Organization and others have been telling people to eat less salt. Cutting 50% of the salt in our diets could save 150,000 lives a year, the AMA estimates.
These entreaties - which have taken on renewed vigor of late - have so far fallen on deaf ears. The average American adult consumes twice the 2,300 milligrams (about a teaspoon's worth) recommended for most adults by the Institute of Medicine and the Department of Health and Human Services' Dietary Guidelines for Americans.
To help people do what they can't seem to do on their own, in the last few years a consumer advocacy group and several medical organizations and health experts have been pushing for legislation that would regulate sodium content in the foods we buy.
They say that more than 75% of the salt we get comes from processed foods and restaurant dishes, making it easy to blow a day's allotment in a single meal without even picking up the saltshaker.
A McDonald's bacon, egg, and cheese biscuit contains 1,250 milligrams of sodium. Frozen entrees in grocery stores can easily top 5,000 milligrams. A typical serving of jarred tomato sauce packs more than 700 milligrams - even bread often has a couple of hundred milligrams per slice.
A few researchers studying the link between salt and health say salt has been unfairly villainized. They argue that only a fraction of the population is sensitive to salt's blood-pressure-raising effects, that our fixation on salt distracts us from focusing on what's really responsible for our nation's epidemic of heart disease, namely, obesity. They say for some people, lowering sodium intake might be harmful.
But the vast majority of such researchers believes the science indicting salt overconsumption is clear. "There's very broad consensus on this," says Dr. Darwin Labarthe, director of the Division for Heart Disease and Stroke Prevention at the Centers for Disease Control and Prevention in Atlanta. "Excess salt is clearly bad for us."
Effects of diet
Strong evidence of this comes from a series of studies called DASH, for "Dietary Approaches to Stop Hypertension." Funded by the National Heart, Lung, and Blood Institute, a division of the National Institutes of Health, the studies set out in the 1990s to discover how diets affect blood pressure.
Blood pressure measurements use two numbers to indicate how hard it is for the blood to get through the arteries, veins and smaller blood vessels. A reading of 120/80 or less is ideal. Hypertension is defined as blood pressure that is consistently higher than 140/90. Pre-hypertension lies between.
In the first DASH study, for two months, researchers carefully controlled what went into the mouths of more than 450 people. One group ate a normal American diet, that is, one with typical amounts of fat and cholesterol. Some ate the same diet with extra fruits and vegetables. And a third group ate what became the recommended DASH diet: full of fruits, vegetables, whole grains and low-fat dairy foods, and low on red meat, sweets and saturated fats. All diets contained about 3,000 milligrams of sodium.
Within two weeks, researchers measured a reduction in blood pressure among the second group, but the third group experienced a drop that was twice as big - a decrease of 5/3 mm Hg - suggesting that a healthful diet can have a large effect on heart health.
Statistics zero in
Armed with that information, the researchers embarked on a second version of the study that aimed to quantify what salt contributes to the blood pressure equation. More than 400 participants ate either a regular American or a DASH diet for three months. For a month each, every participant's food contained either 3,300, 2,300 or 1,500 milligrams of sodium.
(A limit of 1,500 milligrams is recommended for African Americans, anyone middle-aged or older and those with high blood pressure and other health problems - groups particularly sensitive to salt's influence on blood pressure.)
Results of the study, published in the New England Journal of Medicine in 2001, were dramatic, says Eva Obarzanek, a registered dietitian and research nutritionist with the National Heart, Lung, and Blood Institute and a coauthor of the study.
"It showed in a stepwise fashion that if you reduce sodium, you reduce blood pressure," she says.
Specifically, switching from a regular, high-sodium diet to a low-sodium (1,500-milligram) DASH diet resulted in a blood pressure dip of 8.9/4.5 points. That's about the same reduction achieved by blood pressure medication, Obarzanek says, and it often takes two or three drugs to get similar results.
How salt raises BP
Chemically known as NaCl, salt crystals have two parts: sodium and chlorine, which break apart when put into liquid. The chlorine component doesn't do much, but sodium is an essential nutrient that helps keep our hearts beating, nerves firing and body fluids at healthy levels.
When it comes to blood pressure, consuming extra sodium causes the body to retain fluids and boost blood volume to maintain an optimal concentration of sodium in the bloodstream. The heart then has to work extra hard to squeeze all that extra blood through veins and arteries, and blood pressure rises as a result.
The Salt Institute, a trade group in Alexandria, Va., does not think that salt is guilty of everything it's blamed for. "People don't know the whole story," says Morton Satin, a molecular biologist and director of technical and regulatory affairs for the institute. "There are so many questions left to answer."
Dr. Michael Alderman, professor of medicine at the Albert Einstein College of Medicine in New York, is also unconvinced of the danger of salt for most people. "The body has a mechanism of maintaining normal blood pressure over a wide range of sodium intakes," he says. "It's a wonderful system."
Only in people whose kidneys aren't working properly, Alderman says, does excess sodium lead to a rise in blood pressure. Sensitivity to salt, he says, affects just 25% to 30% of people.
But for the majority of health experts, the data linking salt to hypertension are strong enough to recommend that everyone start cutting salt intake - now. Even if salt raises blood pressure in only some of us - and the concept of salt sensitivity remains controversial - there is no reliable way to determine who those people are, Obarzanek says. (For a more detailed discussion of the science of salt, go to latimes.com/health.)
The question, most health experts say, is not if we should lower our salt intake, but how. It's a tough question to answer because salt is a tough habit to break. Because the human body needs salt to survive, we appear to be born with a powerful desire for it. Studies show that infants as young as 4 months old prefer sodium-enriched formula. (Recent studies also show that even kids experience a blood pressure rise when they eat more salt.)
Hooked on salt?
And when people are given increasing amounts of salt, they rapidly develop a preference for it - the saltier the better, says Gary Beauchamp, director of the Monell Chemical Senses Center in Philadelphia. It only takes a couple of weeks to ramp up the salty tooth, he says, even for people from cultures that have traditionally eaten a low-sodium diet.
Getting used to less salt, on the other hand, often takes up to three months, Beauchamp's research shows, and the process can be unpleasant. When you're used to eating regular potato chips, sauces and fast foods, low-sodium or sodium-free foods can taste like cardboard at first.
"In almost all the studies I know that reduce salt abruptly, people were very miserable," Beauchamp says. "In our studies, it is easier to go up than to go down."
But, he adds, "People can change," and studies suggest that maintaining that change is possible - albeit not easy, because salt is so abundant and passes unnoticed in so many of our processed foods. "I would say in our society, it requires constant vigilance."
Changing our eating habits also requires willpower and motivation, which most of us don't necessarily have in abundance when it comes to salt. Surveys show that Americans just aren't that concerned about sodium, says Michael Jacobson, executive director of the Center for Science in the Public Interest, a consumer advocacy group.
And even when we do try to cut down, our best efforts often fail to make much of a difference. How many people know that there are more than 4,500 milligrams of sodium in a Dunkin' Donuts salt bagel or that two slices of Pizza Hut's Thin 'n Crispy Supreme Pizza have 1,460 milligrams? "Awareness stops at the saltshaker," Jacobson says. "People might say they try not to add too much salt to their food without realizing that the vast majority of sodium we swallow comes from packaged foods or restaurant foods that are pre-salted."
In fact, the saltshaker accounts for just 6% of the sodium we consume and the salt we add to recipes makes up just 5%, according to Jacobson's group. Twelve percent occurs naturally in our foods, and a whopping 77% is hidden in processed foods.
In 2005, the Center for Science in the Public Interest issued its most recent petition demanding that the Food and Drug Administration act to regulate sodium content in processed foods. The group also wants warning labels on high-sodium products, sodium levels listed on restaurant menus and brochures, and target levels set for a variety of manufactured foods.
Some countries have already taken similar steps, including New Zealand, France and Ireland.
In the UK, which has launched one of the most massive sodium-reduction campaigns anywhere, the British Food Standards Agency puts strong pressure on manufacturers to meet sodium limits on 85 categories of processed foods, such as bread, cereal and pizza. The industry has responded with significant reductions in their products.
In Finland, which started its own campaign in the 1970s, labels must announce that a product is high in sodium if the content is higher than a set level.
Since the campaign began, Finns have lowered sodium consumption by an average of 30%. In that time, there has been a 10-point nationwide drop in blood pressure, more than a 75% reduction in cardiovascular disease in people younger than 65 and a more than six-year increase in life expectancy. (Several health measures were taken during that time, so salt reduction is a suspected, though not proven, contributor to those trends).
The Center for Science in the Public Interest is pushing the FDA to consider salt a food additive - and regulate it as such - instead of maintaining its current classification, "generally recognized as safe." The group is also urging the food industry to voluntarily reduce sodium in packaged products and restaurants by 50% over the next 10 years.
Such demands are not too much to ask, Jacobson says. Many manufacturers and restaurants already make two versions of their products - a saltier one sold in the United States, and a lower-sodium one sold overseas. Kellogg's Corn Flakes, Rice Krispies and Special K cereals, for instance, have about 36% more sodium in the U.S. than in the UK, according to analyses by Jacobson's group.
Chicken McNuggets, French fries and Big Macs have 46% more sodium in American McDonald's restaurants than in British ones. People there seem to have adjusted to the reduction without difficulty.
For now, the only regulations that exist here allow "low-sodium" labels on products with less than 480 milligrams per serving. "It's moving in the right direction, but it's hardly enough," says Labarthe of the CDC. "The fact is, there is too much salt in our food and too much salt on the market shelf."
The FDA agreed to hold a public hearing in November 2007, at which the Center for Science in the Public Interest and a variety of health organizations and public health officials argued their case for more salt regulation. At the hearing, among other testimony, Los Angeles County Department of Public Health commissioner Dr. Jonathan Fielding reported that the county's rate of high blood pressure increased from 18% to 25% between 1997 and 2005, and said that salt regulation is a necessity.
As research continues and legislation lags behind doctors' urgings, consumers wanting to avoid salt are on their own.
It may be worth the effort, Labarthe says - for your taste buds as well as for your heart. On a trip to Italy a few years ago, he and his wife stayed with a friend who was eating as little salt as possible for health reasons. She cooked for them during their stay.
"On the first night," Labarthe says, "my wife and I looked at each other with the same thought: 'What is the matter with this food?' " By the third day, they could begin to taste the tomatoes in the tomato sauce. By the end of the week, they didn't miss the salt at all, and were appreciating their food more than ever.
"Ever since," he says, "We eat less salt than we ever did."
Sohn is a freelance writer. firstname.lastname@example.org.