Is the war on salt justified?

‘Science-ish’ considers the evidence


Photo by somethingstartedcrazy/Flickr

The Statement: “People who eat a high-sodium diet can be putting themselves at risk of high blood pressure that can lead to heart attack and stroke.”—The Chronicle Herald, 08/03/2011

After decades of attempts by policy makers to wean people off the white stuff, it is now taboo to grab the salt shaker at a restaurant and pour it like snow on your dinner. The wisdom that salt is bad is often reinforced in the media. Just this week, the Chronicle Herald ran a piece about how to “shake your salt habit,” as if sodium were akin to tobacco or cocaine. The Globe and Mail also published on a new scare study, which revealed that 70 per cent of infants consume too much salt. Parents were warned that side-effects could be “more serious than having bloated babies… too much salt in an infant can lead to poor kidney development (and kidneys are the organs that help us skim salt from our blood).”

But what kind of evidence do we have to justify the war on salt?

Let’s start with last month’s Cochrane systematic review, which looked at studies that measured the effects of dietary interventions that restricted salt consumption (and not just the effects of restricting salt consumption, as an earlier version of this article stated. Thank you Science-ish reader Scott Gavura.) The review found that giving dietary advice to individuals about reducing salt intake was not effective at actually reducing consumption, which led to the conclusion that there was no clear evidence to show these interventions cut the risk for heart attacks, strokes or death in people with both normal and high blood pressure.

Science-ish contacted the authors of this study, and Dr. Shah Ebrahim got back to us with his take on the findings. “The likely explanation for lack of any big effect on blood pressure and on deaths is that it is very difficult for individuals to stick to a low-salt diet for many years. It is likely that participants in these studies initially followed advice to reduce salt, but were not able to maintain this in the long term, which contributed to the lack of health benefit.”

Another recent (though controversial—see this link) study, published in the May 4 issue of The Journal of the American Medical Association, found that the less salt people consumed, the more likely they were to die of heart disease. Dr. Jan A. Staessen, the study’s lead author, told the New York Times, “If the goal is to prevent hypertension (with lower sodium consumption) this study shows it does not work.”

The tenuousness of the evidence linking reduced salt consumption to good health has been demonstrated in earlier studies, which have concluded that we do not have enough proof to know how eating less salt impacts human health and mortality. For example, a 2002 systematic review published in the British Medical Journal stated that a policy of reduction in salt intake for an entire population “can achieve small reduction in blood pressure across the whole population for sustained period of time […] However, raised blood pressure is only one risk factor for cardiovascular disease and overall clinical benefits (or harms) of a low sodium diet are unclear.”

In 2008, a systematic review entitled, “Effects of low sodium diet versus high sodium diet on blood pressure, renin, aldosterone, catecholamines, cholesterols, and triglyceride” delved into the salt controversy, and came out with similarly muddled conclusions. “Short-term studies show that in people with elevated blood pressure low salt diets lead to drops in blood pressure, but overall harms or benefits are not known.”

Science-ish contacted one of the researchers behind the latter study, Dr. Niels Graudal of the Copenhagen University Hospital, to get some advice about what would happen if a person decided to reduce his or her daily sodium intake by about 50 per cent, from a normal level of some 3.5g (the Canadian average) to about 1.8g. He said that while this dietary change will mean reduced blood pressure in healthy people and those with high blood pressure, it will also activate the sodium conserving endocrine system, resulting in an increase in renin (an enzyme in the kidneys that promotes the production of angiotensin, which are peptides that control blood pressure) and aldosterone (a hormone that regulates salt and water balance in the body). As well, the dietary change will activate the sympathetic nervous system and may increase the levels of triglyceride and cholesterol in the blood. “The effect on blood pressure, although small, may be good, the other effects may be bad,” he said. “Nobody knows what the net effect of all these effects is on morbidity and mortality.”

He also warned that people should be wary of a lesser-known salt hazard: consuming too little. “Very low levels of sodium may lead to hyponatriaemia (low sodium concentration in the blood), which is dangerous and may lead to brain damage and in the worst case death.” He added: “Sodium is one of the most essential components of the body without which life is not possible.”

Science-ish is a joint project of Maclean’s, The Medical Post, and the McMaster Health Forum. Julia Belluz is the associate editor at The Medical Post. Got a tip? Seen something that’s Science-ish? Message her at julia.belluz@medicalpost.rogers.com or on Twitter @juliaoftoronto


Is the war on salt justified?

  1. Interview with Marion Nestle: 

    A:  …… But if you do a clinical trial where you try to put large amounts of people on a low-salt diet, you just don’t see much difference between the people who say they eat a lot of salt and the people who say they don’t eat a lot of salt. In clinical trials the relationship doesn’t show up. 

    Why not?

    A: Two reasons: One that it’s impossible to put a population of people on a low-salt diet. Roughly 80 percent of the salt in the American food supply is in foods before people eat them—either in processed food or in restaurant food. Because so much salt is added to the food supply and because so many people eat out, it’s impossible to find a population of people who are eating a low-salt diet. They basically don’t exist ….. 

    What’s the other issue? 

    A: Not everybody responds to a low-salt diet. There’s a proportion of people in the population who are sensitive to salt—if you lower their intake of salt, then their blood pressure goes down. There’s another (probably larger) percentage of the population who doesn’t respond. They are people who can eat as much salt as they want and still their blood pressure is low. So you have this curious anomaly where whenever you do a clinical trial you get these complicated, difficult-to-interpret results that don’t show much of an effect. 


    It’s Time To End War On Salt:

    For decades, policy makers have tried and failed to get Americans to eat less salt. In April 2010 the Institute of Medicine urged the U.S. Food and Drug Administration to regulate the amount of salt that food manufacturers put into products ….. 


  2. I have faithfully salted my food all my life….even through the years when people tut tutted at me for doing so.

    I knew eventually they’d realize, once again,  that salt is necessary to Life.

  3. I suspect a person would need to live on an uninhabited planet to be at risk for developing hyponatriaemia: Sodium is contained in just about any fruit and vegetable. Restaurants and prepared food manufacturers must think you have to add it by the tablespoonful, instead of just a shake or two. Whenever I eat out, my mouth burns from the quantities of salt used in cooking. I find soups, in particular, to be nearly inedible due to the excessive quantities of salt used.

    Disregarding the science altogether, let us step up the war on salt and start having our food taste good again, so that we can begin to enjoy the flavours of foods tastefully seasoned with herbs and spices, instead of having everything taste exactly the same and leaving our mouths burning with salt.

  4. What we are talking about here is not salt itself, but too much salt.

    You point out correctly that both salt and sodium are needed for life.  But there are significant negative health effects if you have too much or sodium.Also, those who are suffering from high cholesterol or high blood pressure have other problems with their diet and exercise programs than just salt or sodium content.  So any study would have to take into account other lifestyle factors than just a patients salt content or sodium content.

    Warm Regards,
    Tony Rovere

  5. Oh, for the love of god. How many red flags do you need before jumping into half-assed iconoclasm?

    The world is full of TonyAdams, who just LOVE to proclaim those smartypants “experts” wrong, wrong, wrong. But a paid journalist ought to know selection bias when she sees it. You actually write “But what kind of evidence do we have to justify the war on salt?”, taking it for granted that there is some ideologically/politically-driven “war on salt”.

    Quotes from your own cited articles:

    “Part of the problem is that individuals vary in how they respond to salt.”

    “One oft-cited 1987 study published in the Journal of Chronic Diseases reported
    that the number of people who experience drops in blood pressure after
    eating high-salt diets almost equals the number who experience blood
    pressure spikes; many stay exactly the same.”

    “Some physicians argue that although tiny blood pressure drops will not
    have a big effect on individuals… they may end up saving lives at the population
    level, in part because a small percentage of the population… seem to be
    hypersensitive to salt.”

    [The above quotes lay out a mechanism by which low-sodium diets may have a large impact at the population level]

    “This review set out to assess whether advice to cut down on salt in
    foods on altered our risk of death or cardiovascular disease. Intensive
    support and encouragement to reduce salt intake did lead to a reduction
    in salt eaten and a small reduction in blood pressure after more than
    six months. There was not enough information to understand the effect of
    these changes in salt intake on deaths or cardiovascular disease.”

    “Trials fulfilled the following criteria: (1) randomised with follow up
    of at least six-months, (2) intervention was reduced dietary salt
    (restricted salt dietary intervention or advice to reduce salt intake),” (ie. we coached subjects to eat less salt)

    “Despite collating more event data than previous systematic reviews of
    randomised controlled trials (665 deaths in some 6,250 participants),
    there is still insufficient power to exclude clinically important
    effects of reduced dietary salt on mortality or cardiovascular morbidity
    in normotensive or hypertensive populations.”

    [Those quotes show how little information contradicts the notion of sodium reduction as a good thing]

    …despite the virtues of a randomized controlled clinical trial, such a
    study “will never ever be done.” It would be impossible to keep people
    on a low-sodium diet for years with so much sodium added to prepared

    “The low-salt advocates suggest that all 300 million Americans be
    subjected to a low-salt diet. But if they can’t get people on a low-salt
    diet for a clinical trial, what are they talking about?”

    That last quote is the money shot. Sounds like every wanker climate-change/evolution denier in a borrow lab coat, casting the world into advocates of one policy vs. skeptics who know better (but never quite offer proof of their own stance).

    Really, it sounds like Ms. Belluz just read a few newspaper and magazine articles and summarized the “controversy” all by herself.

    Better science writing, please.

  6. Sad. I had high hopes for this column, but this post has crushed them. Way to confuse the ineffectiveness of dietary interventions on salt reduction, and the effects of salt on health! This article is full of almost ideological wording and cherry picking of studies to fight some imaginary foe.

  7. In any of this discussion we need to be sure about where we are starting from. In the UK the Food Standards Agency said in 2008 “UK’s average daily salt consumption has fallen from 9.5g to 8.6g, and reflects an overall drop of 0.9g since the National Nutrition and Diet Survey (NDNS) in 2000/01”. 
    If you are right that the Canadian average is 3.5g then there is very little point in comparing advice or intake policies between the two countries.  A sucessful policy aimed at reducing UK intake by half would probably have a very different effect if applied to Canada.

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