Assault on the System
Decades of meticulous science proved that a low-sodium diet could reduce your blood pressure. Now comes the tricky part: extracting salt from the food supply.
On a Monday morning last January, New York City Mayor Michael R. Bloomberg stepped in front of cameras and reporters at City Hall to announce a new public health campaign of astounding ambition: The Mayor and his health department, supported by more than 50 other city and state governments and health associations, intended to cut Americans’ average salt intake by 20 percent over the next five years, by targeting the excess salt in processed foods and restaurant foods. The National Salt Reduction Initiative (NSRI) would rely on the voluntary cooperation of food companies and restaurant chains, but it aimed to affect hundreds of commonly consumed items, from Kraft bacon to Heinz ketchup and Subway subs—not just in New York City but across the country. “We have been able to accomplish something that many thought was impossible: setting concrete, achievable goals for salt reduction,” Bloomberg said.
Previous salt-reduction efforts have been aimed at individual consumers. For decades, doctors have advised their patients with high blood pressure to cut the salt, and more recently the federal government has begun encouraging all Americans to do the same. Yet our salt intake has been rising, and our epidemic of hypertension—now afflicting about a third of all American adults—has been worsening. According to the most recent national survey, we consume about 3,400 mg of sodium per day on average (sodium being the salt ingredient of chief concern), while a healthy sodium intake for most of us would be at or below 1,500 mg per day—roughly the amount in two-thirds of a teaspoon of salt.
Our sodium intake is high because excess sodium is basically baked into our food supply. Nearly 80 percent of the sodium we consume comes from processed and restaurant foods—compared to only about 11 percent from our saltshakers. Some products these days can push our intake over the healthy limit in a few bites. A McDonald’s Big Breakfast with Hotcakes, for example, delivers more than 2,000 artery-thumping milligrams of sodium. Even seemingly healthy, non-salty-tasting foods are a potential hazard; one can easily get half the daily recommended sodium limit from a few slices of store-bought whole wheat bread.
“Sodium is in almost everything we eat, so we don’t have as much control over our intake as we’d like to think,” says Lawrence Appel, MD, MPH ’89, a professor of Medicine, Epidemiology and International Health and a faculty member of the Bloomberg School and the School of Medicine’s Welch Center for Prevention, Epidemiology and Clinical Research.
Thus, NSRI moves away from the old, demand-side emphasis on consumer education and takes aim instead at the supply-side of salt. Similar efforts have begun recently in other countries, and an Institute of Medicine (IOM) panel, which included Appel and Welch Center epidemiologist Cheryl Anderson, PhD, MPH, MS, concluded in April that the Food and Drug Administration (FDA) should eventually make sodium reductions in food mandatory, not voluntary.
“Now, really for the first time, sodium reduction has become a high priority within the FDA,” says Michael Jacobson, PhD, whose Center for Science in the Public Interest, in Washington, D.C., has been urging the agency to regulate sodium since 1978.
Danger in a World of Plenty
In 1990, Chinese-born physician Jiang He approached Johns Hopkins' School of Public Health with a remarkable story.
For several years, he had been traveling to the remote mountains of southwestern China to study the Yi people, an ethnic minority for whom hypertension—very common elsewhere—was almost unknown. "The mean blood pressure for Yi farmers in their 60s was close to the mean for Yi farmers in their 20s," He remembers. The young researcher was invited to the School to complete his PhD, and produced a series of papers on the Yi, with epidemiologist Paul Whelton, MD, MSc, and then junior faculty member Michael J. Klag, MD, MPH '87.
The Yi were one of the extended tribes that in effect had been chased into the mountains 2,000 years before by the dominant Han ethnic group. In modern times, they had continued to live their traditional lifestyle, and as He had found, their diet was very low in sodium. He and his colleagues at Johns Hopkins subsequently compared the Yi farmers' blood pressures and sodium intakes—measured by collecting urine from subjects for a sample 24-hour period—with those of Yi migrants to lowland cities. It turned out that the Yi migrants, after exposure to a more modern, urban lifestyle, had begun to consume sodium and develop hypertension at rates like those seen for other Chinese.
"This Yi migrant study influenced my career," says Klag, now dean of the Bloomberg School. "It strongly suggested that our high rates of hypertension come from a real mismatch between how we evolved and how we live today."
For nearly all of the period in which modern humans evolved, sodium intake had been a small fraction—on the order of 100 mg daily—of what it now averages in modern diets. Only in the past few hundred generations (or past few generations, for some) had salt been used as a flavor enhancer and preservative. As for so many other things in modern life, a strong pleasure-sense that had evolved to steer us toward a scarce necessity now had come to endanger us in a world of plenty.
Convincing Evidence
Sodium is one of the essential elements used by cells, and its concentration in the human bloodstream is meant to be kept within a narrow range. When excess dietary salt enters the blood, more water is drawn into the bloodstream to compensate—which is why a salty meal is apt to make us thirsty. This increase in blood volume tends to raise blood pressure, especially for those whose blood vessels are less flexible. The kidneys can push blood pressure down again by filtering excess sodium from the bloodstream and excreting it via urine, but kidney function also tends to decline with age—and with hypertension—so that a chronic salt overload may trigger a vicious cycle of declining kidney function leading to rising blood pressure and further declines in kidney function.
Hundreds of experiments in humans and lab animals have confirmed that excess sodium intake is apt to raise blood pressure. Studies of pre-modern cultures such as the Yi have shown that low-sodium diets tend to be associated with low rates of hypertension. Studies of modern populations and patients also have concluded that hypertension is a major risk factor for cardiovascular disease, strokes and kidney disease—three leading causes of death in the Western world. Epidemiologists have estimated that even a slight downward shift in Americans' blood pressures, especially for those near or above the hypertension limit, would reduce these disease risks enough to prevent at least tens of thousands of deaths annually.
Why, then, has it taken so long for policymakers to consider restricting sodium's presence in the food supply?
One reason is that the medical profession hasn't always approached it as a public health problem. "Early on, there was more of an emphasis on treating people who have heart disease, for example, and then there was the idea of treating people who have risk factors for heart disease, such as hypertension," says Appel. "Only recently have we started to think in terms of preventing hypertension in the first place, using population-wide public health strategies."
And only recently has there been the convincing evidence needed to justify a public health approach. Population-comparison studies, for example, showed an association between a low sodium intake and a low rate of hypertension, but they couldn't untangle the effects of other dietary and lifestyle factors. To justify a strong sodium-lowering public health campaign, large-scale clinical trials of sodium reduction were needed. The three most prominent of these trials were all conducted from the late 1980s to the early 2000s.
The first was set up by Whelton with NIH funding in 1986, and included Klag and Appel, then a postdoctoral fellow. It was known as TOHP (for "Trials of Hypertension Prevention") and among other things, it indicated that for a group of people with moderately high blood pressure, even a slight reduction in their average pressure, via a reduced sodium intake, could markedly reduce the number of cases of hypertension.
A second study, known as TONE ("Trial of Nonpharmacologic interventions in the Elderly"), was set up by Whelton in the early 1990s, and included a sodium-reduction study designed by Whelton and Appel. It found that in several hundred elderly people, a one-third reduction in normal salt intake per day lowered blood pressure readings by 4-5 millimeters of mercury on average, compared to a control group. The improvement was sustained over 30 months and included a sizable drop in the relative occurrence of bad outcomes, such as cardiovascular problems or having to resume medication.
Then in the late 1990s came the "DASH-Sodium Trial" ( "Dietary Approaches to Stop Hypertension-Sodium Trial"). Appel served as one of its lead investigators. The study showed clearly that for people with higher-than-normal blood pressure or outright hypertension, moderate or strong reductions in sodium intake brought about correspondingly moderate or strong reductions in blood pressure—whether their diet emphasized fruits and vegetables or the meatier and fattier offerings typically found on America's tables.
"That turned out to be one of the most persuasive studies of sodium and blood pressure," says Appel, "because it showed a clear dose-response effect in which greater sodium reduction led to greater blood pressure reduction."
"The DASH diet studies that Larry Appel and others conducted were really the tipping point for a lot of people, in terms of justifying a more aggressive public policy on this issue," says Daniel Jones, MD, a prominent hypertension researcher who is now chancellor of the University of Mississippi.
From Science to Policy
More recent studies have continued to highlight the threat posed by too much salt in our diets, and the need for a strong preventive approach. “The evidence now suggests that if your blood pressure goes up, you’ve already started to incur organ damage,” says Anderson. “If you wait ’til age 50 or 60 to get treatment, irreversible damage may have set in.”
Skeptics have expressed concerns that a steep and sudden reduction in sodium in the food supply could end up having adverse effects. But even the ambitious 20 percent reduction targeted by NSRI would be gradual and would take us back to the still-excessive levels of the 1970s. “The idea that harm would come from this level of sodium reduction is a myth,” says Appel.
“As far as I and many other public health officials are concerned, the necessary science on this has been done,” says Sonia Angell, MD, a New York City Health Department official who helped set up NSRI, and also sat on the recent IOM sodium-reduction panel. “The World Health Organization, the American Medical Association, the American Heart Association and the U.S. government in their Dietary Guidelines for Americans all have concluded that there’s too much salt in the diet. So I think the challenge that we face now is how to move it out of our food supply.”
Small-scale studies have shown that the sodium content of many processed foods can be reduced gradually without making diners reach for their saltshakers. And a number of countries, including Finland and the UK, have already found that sodium-reduction programs can work at the population level.
The UK’s effort began in 2003 and includes progressively tightened targets for sodium reductions by the UK food and restaurant industry. The initiative is voluntary but is clearly backed by the possibility of formal regulations. Its overall goal is to reduce the UK population’s average daily sodium intake to 2,400 mg. Dozens of UK food companies are on board, the average sodium content in many food categories has dropped sharply, and the average UK intake has fallen by 10 percent from 2001.
“The UK’s model in particular demonstrated to us that there was an effective way to approach this,” says Angell.
As of this April, NSRI had obtained sodium-reduction pledges from 16 U.S.-based food and restaurant companies, including Heinz, Goya, Subway, Starbucks and Kraft. Like the UK initiative, NSRI specifies maximum average sodium levels for different categories of processed foods and restaurant foods. There is an initial set of targets to be met by 2012, and a tighter set for 2014. Kraft, for example, has pledged to meet the specified 2012 targets in half of NSRI categories that cover its foods, including a 17 percent reduction in sodium for its Oscar Mayer bologna.
NSRI aims for an overall 25 percent cut in sodium in America’s processed and restaurant foods by 2014, which, if achieved, should cut Americans’ overall sodium intake by about 20 percent. But for many products, meaningful sodium reductions will reduce palatability and/or shelf life, which could make it hard for companies to comply voluntarily. While the IOM panel encouraged voluntary-based initiatives such as NSRI, its primary recommendation was that “the FDA should expeditiously initiate a process to set mandatory national standards for the sodium content of foods.”
FDA action could be years away, but the prospect of formal regulation, plus the scientific evidence that now links excess sodium to tens of thousands of excess annual deaths, has gotten the attention of the food industry. Most of the companies that signed up for NSRI had already been gradually and quietly reducing the sodium in their products.
That’s also the case for companies that haven’t joined NSRI. Campbell’s Soup Company, for example, claims to have reduced the sodium load in its original V8 juice by a third since 2002. During the IOM panel’s deliberations, says Anderson, “a representative of one of the fast-food chains gave a talk, and said that on their own they’d already cut the salt by about 70 percent in one of their menu items—and no one even noticed.”
“Some in the food industry have dug in their heels on this, but most have been moving in the right direction,” says Appel. “They want to stay ahead of the curve.”