From Heartwire

Ripe For Change: US Ponders Populationwide Salt-reduction Policies

March 23, 2010

January 29, 2010 (London, UK) — In most developed countries, more than 75% of the salt consumed comes from processed foods: simply getting people to stop using salt is only the tip of the iceberg when it comes to sodium reduction.

The US is a case in point. For 40 years, health advocates have struggled to educate citizens about reducing salt intake, yet the per capita consumption appears to be increasing or is at best unchanged. This is "incredible, given the amount of money that has gone into public-health initiatives," says Dr Cheryl AM Anderson (Johns Hopkins University, Baltimore, MD).

"People are not aware of how much salt they consume, and they are struggling to meet the recommendations," she says. Much of this is due to "the ubiquitous nature of sodium in the food supply," she explains. "Sodium comes in the form of things that people don't traditionally think of as salty. So they don't add salt to their food at the table, but they are getting salt from the foods they eat in restaurants or from take-out. Also they are getting it through heavy consumption of breads, grains, and cereal products and, again, these aren't foods that we would traditionally think 'Oh they contain salt,' which makes it very difficult for people to do what they need to do."

But things may soon change if, as widely predicted, the US joins a number of other developed countries in instituting policies to try to reduce the amount of salt in the diet of the whole population.

Because consumers themselves are fairly powerless to cut their salt intake in Western nations, the cooperation of the food and restaurant industries is crucial, explains Dr Feng J He (Queen Mary University of London, UK), who has authored a number of reviews on the subject of salt-reduction programs worldwide. "If you can get the food industry to gradually reduce the amount of salt added to its products, salt intake can be cut and the general public doesn't have to do anything; they won't notice at all; it's easy," she says.

As well as overwhelming evidence that dietary salt is the major cause of raised blood pressure, most experts agree that even a modest reduction in salt intake at the population level will lead to fewer strokes and heart attacks.

A number of countries have already successfully implemented salt-reduction programs, including Japan, Finland, and most recently the UK, by enlisting the help of the food industry, either voluntarily or by enacting legislation. Others—including Australia, Canada, Ireland, and the Netherlands—are starting to step up activities in this area.

Anderson, an epidemiologist with a primary interest in nutritional factors relating to cardiovascular-disease prevention, sits on a panel convened by the US Institute of Medicine (IoM), which has been commissioned to issue a report, "Population-based strategies for reducing salt intake," due to be released this spring. While she can't reveal the contents of the upcoming report, she believes the time is ripe for change.

Salt: Is your food full of it?

In a recent review,[1] He and her colleague Dr Graham MacGregor (Queen Mary University of London, UK), explain that in ancient times, humans consumed less than 0.25 g of salt per day; the modern use of salt can be traced to about 5000 years ago when the Chinese discovered that it could be used to preserve food. With the advent of refrigerators and freezers, salt was no longer required for preservation, so intake started to decline.

But then the large increase in consumption of processed foods in the Western world once again led to higher intake, because "salt makes cheap, unpalatable food edible at no cost," says He. Salt is used in many meat products to bind in water, thereby increasing product weight, and is a major determinant of thirst; many of the largest snack firms in the world also have soft-drinks arms, so they have a vested interest in keeping the status quo, she says.

Some members of the food industry have therefore tried to make salt a controversial issue relative to other dietary changes, she says, and "their strategies are identical to the techniques used by the tobacco industry." But food companies should have nothing to fear from gradually reducing the salt content of foods, she maintains. Indeed, the opposite is true: if people eat more healthily, they will live longer and there will be an increased number of consumers, she says.

In the US, the current daily recommended upper limit for salt intake is 5.8 g (2.3 g of sodium, which makes up 40% of the weight of salt), which is based, says Anderson, on data from prospective epidemiologic studies, "where you look at where the association with risk changes; you look at when adverse health outcomes start to happen." In addition, 69% of US adults have even stricter recommendations of an upper limit of just 3.8 g of salt per day, including those who have existing hypertension, those who are middle-aged or older, and African Americans, she says.

Upper limits for children are also lower, with targets calculated by the UK Scientific Advisory Committee on Nutrition ranging from 5 g a day for seven- to 10-year-olds to 2 g per day for one- to three-year-olds and <1 g per day for those under six months of age.

Other countries have similar recommendations. The WHO advises that adults consume no more than 5 g per day, but many governments consider 6 g to be a more realistic target. As the average consumption of salt in most Western countries currently stands at around 9 g to 12 g a day and is even higher in some Asian countries, there is obviously a long way to go to achieve even these practical goals.

The targets are really based on "what it is thought possible to achieve in the population rather than the potentially maximal beneficial effect," says He. And as such, the best contemporary approach to salt reduction in the West is felt to be a public-health approach: a modest but prolonged reduction in sodium intake across the population as a whole, fueled by persuading the food, restaurant, and other industries to reduce the salt content of their products.

This approach also gets around the problem of salt sensitivity: variations in blood-pressure response to salt reduction, say He and MacGregor. Almost all studies on salt sensitivity have used a protocol of very large and sudden changes in salt intake, they explain; the modest reduction that they propose, carried out universally in the entire population, lowers population BP by a small amount yet has a large impact on reducing the "appalling" burden of cardiovascular disease. "Even a modest reduction in population salt intake worldwide would result in a major improvement in public health—similar to the provision of clean water and drains in the late 19th century in Europe," they advocate.

Salt intake in UK has fallen by 10% as a result of campaign

He and MacGregor, as part of the campaign group, the Consensus Action on Salt and Health (CASH), have helped to spearhead a public-health drive in the UK to reduce salt intake, which has already reported some success. Food manufacturers there were encouraged by the Food Standards Agency (FSA) and CASH to voluntarily lower the salt in their products from 2003 onward and to develop lower-salt alternatives as well as to provide information about the sodium content of foods at the point of purchase. Consumers were also blitzed with information regarding the harms of excessive salt via the media and encouraged to examine the salt content of all foods purchased.

The campaign has so far succeeded in reducing population salt intake by about 10% (from 9.5 g to 8.6 g a day), and last year the targets for the food industry were tightened even further.

He told heartwire she strongly supports the introduction of a similar populationwide initiative to reduce salt in the US and elsewhere, which she says will have a larger impact on CVD than other lifestyle changes such as weight reduction and physical exercise.

The World Action on Salt & Health (WASH), established in 2005, would also like to see campaigns such as the one under way in the UK extended to all countries. WASH's World Salt Awareness Week, running this year from February 1 through February 7, will focus on raising public awareness not just about the link between a high salt diet and high blood pressure, but also about the increased risk of stroke, osteoporosis, obesity, stomach cancer, and kidney stones. Excessive sodium intake can also contribute to left ventricular hypertrophy and congestive heart failure and to an increase in the severity of asthma.

In July 2009, WASH surveyed over 260 products from food manufacturers around the world such as KFC, McDonald's, and Kellogg's and found surprisingly widespread variations. For example, Kellogg's All-Bran for sale in a number of EU countries contained 1.30 g of salt per 100 g compared with salt levels of 0.65 g per 100 g for the product in the US. The results underly the urgent need to eradicate country-to-country inequalities and bring everyone up to the highest possible standards, says WASH.

Reducing salt in US population would be "an experiment"

Although the majority of experts support the view that populationwide policies on salt reduction are the way to go, there are a handful of doubters. Dr Michael Alderman (Albert Einstein College of Medicine, Bronx, NY) is a self-confessed cynic.

"My stance is based on what I see of the science of the issue," he told heartwire. He argues that although there is no doubt that reducing sodium intake reduces blood pressure, salt also has a myriad of other biological effects. The clinical-trial evidence that reducing salt actually affects hard outcomes such as heart attacks and strokes "is all over the place; the whole thing is kind of a mess," he says. "Advocates of salt reduction believe the only thing that matters is the BP effect, but skeptics like me say, 'Wow, that's a stretch.' "

He maintains that a US policy to slash sodium intake at the population level would be "an experiment" and that there is no way of knowing whether it would be beneficial or indeed harmful: "There are many very committed, well-meaning, and zealous partisans for people's health who say, 'Let's go ahead and try it, let's get everyone to lower their sodium intake. We can't be sure what's going to happen—we don't have any direct evidence—but we are so firmly convinced that the BP effect will rule all that we will go ahead and do this,' " he continues. "This strikes me as kind of rash and is based on a firm belief in something that hasn't been proven.

"In folks with a diet like that in the US, there are some studies that show an inverse association—less salt, more heart attacks—so the data are conflicting, and it's a problem," he states. He was involved in some of the analyses he refers to, however, and they have attracted some criticism with regard to methodology. [2]

Alderman maintains that randomized controlled studies are needed, "if we want to have a science-based health policy. I don't really care so much about the number of my blood pressure or the activity of my renin-angiotensin system. I care about how well I live and how long I live, and that's measured by heart attacks, strokes, kidney failure, and death."

And he insists that he is not a naysayer for the sake of argument: "Look, I'd be delighted if such a simple trick as to change one factor in something as complex as the human diet for everybody could save millions of lives. Of course I'd be for that, but I'm not sure."

But Alderman, says MacGregor, is in the minority. "The only people who are against salt reduction, as far as I know, are consultants to the Salt Institute, the major public-relations company trying to unsuccessfully defend any reduction in salt," he told heartwire.

Alderman says he is a member of an advisory committee to the Salt Institute but is unpaid: "I attend an annual meeting of this committee but do not receive speaking fees, research, or any funding from the food industry."

Anderson and He, for their part, are adamant that there is already sufficient evidence that reducing salt in the population has an impact on CV outcomes. Notable among these is a 2007 study published in BMJ[3] by Cook et al that followed patients originally enrolled in trials of hypertension prevention and examined the effects on cardiovascular outcomes of people who continued to maintain their low sodium intake over the next 10 to 15 years.

"This study clearly showed that the people who were originally allocated to the lower-salt group had lower cardiovascular events," says He.

Indeed, the AHA singled out this study as one of its "top 10 advances for 2007," with then-president Dr Daniel Jones (University of Mississippi, Oxford) stating that it was the first major trial to document that a reduction in sodium intake lowers not just blood pressure but the risk of cardiovascular-disease outcomes.

And last year, a meta-analysis by Strazzullo et al, also published in BMJ,[4] covered all prospective studies of salt intake, stroke, and cardiovascular disease and "clearly documents that a reduction in sodium intake is beneficial for stroke and CVD," says Anderson.

In addition to the above trials, says Anderson, are studies such as the one published in the New England Journal of Medicine just last week,[5] "where people have been doing modeling through pretty rigorous methodological approaches," she says. "The evidence is starting to stack up that suggest that reducing salt intake is indeed productive. This is not an experiment of any sort!"

MacGregor agrees: "The recent papers in the New England Journal of Medicine make the case completely overwhelming," he told heartwire.

Hypertension doctors in Europe concur: they are lobbying for EU-wide legislation to be introduced to restrict the salt content of processed foods. "The case for populationwide salt reduction is now compelling," says cardiologist and hypertension specialist Dr Frank Ruschitzka (University of Zurich, Switzerland) in a European Society of Cardiology statement released this week.[6]

Such a move would be "an inexpensive yet highly effective public-health intervention that we can't afford to miss," he added. "The reality of international food production in Europe means that such public-health initiatives need to be tackled on a European-wide basis, rather than an individual country basis."

Action, not outcomes trials, is what's required

Both Anderson and He say that calls such as Alderman's for bigger and longer trials to look at cardiovascular outcomes with salt reduction are simply unrealistic.

For starters, it would be very difficult to keep large numbers of patients on their respective low- or high-salt diets for long periods of time, they say. "The low-salt group would inevitably end up eating saltier food because the environment is so full of it, and those on the high-salt diet would hear the media campaigns about the dangers of salt and start to reduce their intake, and in the end we would have no difference between the groups," He says.

"Also, based on the available knowledge, I don't think it's ethical to keep people on a high-salt diet for many years," she adds. Moreover, "who would fund such a study?" she wonders. Anderson completely agrees: "It's just not practical to fund that kind of effort; it would cost billions of dollars."

"The evidence is strong," says He. "It's time to take action now rather than do more outcomes trials."

Food for thought? Japanese and Finnish success stories

Bolstering He and Anderson's calls for outcomes trials are compelling tales from Japan and Finland, which were the first two countries to really tackle salt intake at the population level, says He.

In the late 1950s, Japan was shown to have one of the highest death rates from stroke of any nation, so in 1960, the government initiated a campaign to reduce national salt intake. Over the following decade, it was reduced from 13.5 g per day to 12.1 g per day, and in certain regions (the north), intake fell from 18 to 14 g per day. Paralleling this reduction were falls in BP in both children and adults and an 80% reduction in stroke mortality, despite large increases in fat intake, cigarette smoking, alcohol consumption, and obesity.

And in Finland, from 1975 on, there was a similar drive to reduce salt intake in the entire population. "Their strategy was similar to the one we are currently employing in the UK," says He. "They educated the public and worked closely with the food industry to develop reduced-salt products." Over the next 30 years, salt intake there fell by a third—this was shown measuring "the gold-standard" 24-hour urinary sodium output, He notes—and this was accompanied by a fall of more than 10 mm Hg in both systolic and diastolic BP and a "remarkable" 75% to 80% reduction in stroke and CHD mortality, and a five- to six-year increase in life expectancy, she notes.

Although she acknowledges that the Finns also significantly reduced saturated fats in the diet and smoking in their population at the same time, which would "all have played a part," she points out that body-mass index (BMI) and alcohol consumption actually increased there during that time period. "So the point I am making is that salt is a major contributing factor for the fall in BP. And BP is a major cause of stroke and CHD," she notes.

In addition, she says there is evidence from animal and epidemiological studies "that salt may have a direct effect on stroke independent of blood pressure. The message is very clear: salt is related to stroke."

Even Alderman accepts that the data from certain populations that have "very high salt intakes"—Japan, northern China, and Finland, for example—illustrate that higher salt intake results in more heart attacks and strokes. "There you've got three or four observational studies that go in the same direction, so it's more hopeful," he acknowledges.

Different approaches needed in different countries
He stressed to heartwire that in developing countries, although a policy to reduce salt in processed foods will be helpful, in many places more emphasis is needed on educating the public about the dangers of adding salt, because much of the sodium in their diets comes from people adding it during cooking, pickling, and preserving. Given the fact that around 80% of global blood-pressure-related disease burden occurs in developing countries, "it is imperative that each one determines what its salt intake is and where the major sources of salt are in the diet" in order to develop strategic approaches to lowering salt intake in their own populations, she says.

And in some circumstances, this will mean having different approaches for different areas of the country, she explained. For example, in urban areas in China, people now eat a lot of processed foods and have less time to prepare their own meals, so their circumstances are similar to Western nations. But in rural northern China, people still use salt to prepare, flavor, and preserve the food they are cooking, and here a different public-health message is required, she says.

A recent study in the Lancet[7] found that high blood pressure is the leading preventable risk factor for premature death in China, with almost 2.5 million deaths there attributable to hypertension in 2005, a "striking and unexpected" figure compared with previous estimates," said the authors.

 

He and MacGregor both report no conflicts of interest.

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