Is It Time to End the “War on Salt”?

Photo: DaGoaty

The assault on dietary salt has been growing, and salt sales have been trending slightly downward. Is this a good fight?

According to Scientific American, perhaps not:

This week a meta-analysis of seven studies involving a total of 6,250 subjects in the American Journal of Hypertension found no strong evidence that cutting salt intake reduces the risk for heart attacks, strokes or death in people with normal or high blood pressure. In May European researchers publishing in the Journal of the American Medical Association reported that the less sodium that study subjects excreted in their urine—an excellent measure of prior consumption—the greater their risk was of dying from heart disease. These findings call into question the common wisdom that excess salt is bad for you, but the evidence linking salt to heart disease has always been tenuous.

(HT: Eric Jones)

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  1. frankenduf says:

    it is a simplification that is indirectly correct- the key is potassium to sodium ratio- the higher ratio of intake, the greater the cardioprotective effect- so it is more effective to eat high potassium diet- also, some are sodium sensitive (eg diabetics) and for them it is directly safer to decrease salt intake

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  2. JR says:

    Remember a few years ago there was a movement to have people eat a pH balanced diet? The purported benefit was more pH balanced blood. But pH is very tightly regulated in the blood and there are several mechanisms to make sure it happens. Blood salinity is the same thing, your body tightly regulates it in the blood and disposes of any excess.
    I’ve always seen the “salt is bad for you” rumor as another too-soon announced study that will lead to more distrust of nutrition science.

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    • Ted Pavlic says:

      Regulation has its limits. For example, if you had no salt intake and had to upregulate to maintain the proper salinity, your body would be stuck. The best it could do is expel excess water until your body was desiccated as well.

      Similarly with pH, your blood pH may be regulated, but this regulatory mechanism doesn’t come for free. A poor protein–carbohydrate balance in the diet can lead to kidney stones. After an incident with struvite crystals in his bladder, my dog was put on a prescription dog food for the rest of his life to reduce the regulation burden on his body, which has a genetic disposition for high pH. Consequently, we’ve also been told to increase the protein-to-carbohydrate ratio of any other food he gets by putting a high emphasis on proteins (which tend to make the blood more acidic).

      Regulation is not free. Imagine any servomechanism in your car; eventually the open-loop servo mechanism will saturate and no amount of feedback you provide will restore the system to its balance until you return the controller to its NORMAL operating region.

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  3. Nosybear says:

    I have to ask how you missed the headline “…Assault on Salt.”

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  4. Priscilla says:

    Apparently the study measured the amount of sodium excreted in urine, and correlated low output with heart disease,etc. This seems to suggest that dietary intake was not what was studied. So, perhaps it is the retention of salt that is the problem, or at least the correlation. Further study could determine why some people retain salt and others, not so much. When I was pregnant and my bood pressure was rising, I was put on a no salt diet (but in those days, mandatory labeling had not come into play so it was years later that I found I was actually eating a lot of sodium!) and my doctor managed to keep things somewhat in check by having me drink large quantities of water! Did the tests ask suibjects how much water they drank? My guess is that people hoo drink a lot of water get rid of a lot of sodium.

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  5. Anusheh says:

    Perhaps… I’m eating less because my food tastes worse

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  6. Sprocket says:

    In one of these studies as I saw it reported the authors explained the fact that lowering salt intake had no effect on stroke/death rates by:

    1) Less salt = lower blood pressure.
    2) Lower Blood pressure = fewer strokes/deaths
    3) Study did not show this to be true.
    4) Therefore we did not lower blood pressure enough, because everyone “knows” these results cannot be right.

    It seems to me there are actually a different set of truths here:

    1) Only in a few people (c25%?) does reduced salt reduce blood pressure.
    2) High Blood pressure is not a factor in death/stroke/heart disease until it is very very high (>200).

    I think you guys at Freakonomics should look at a whole bunch of these medical “truths” and dig deeper into the stats to see how many of them are wrong. Lowering cholesterol would be a good start, along with low fat diets. (If you have already done so forgive me!).

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    • Ted pavlic says:

      To understand salt’s impact on blood pressure, you have to recall what you learned about osmosis in primary and secondary school.

      In particular, the greater the salinity of the blood, the increased flow of water into the blood vessels across semipermeable membranes. This flow (call it osmosis, if you must, but it’s just diffusion of water) continues “until” the salinity is balanced on both sides. I say “until” in quotes because it actually goes on continuously, but the in-flow and out-flow balance at that point and so the net movement of water is zero. At that new point, there will have been more water moved into the blood vessels. That increase in water volume causes either an increase in blood pressure and/or an increase in vessel diameter. Either way, it’s an additional stress.

      You can imagine that these osmotic pressure differentials could cause lots of other problems throughout the body as well. Heck, consider crenation:

      http://en.wikipedia.org/wiki/Crenation

      So I hardly think it’s a fantasy to associate blood pressure with salinity. The question is how the body deals with the hypertonic blood. That’s one of the functions of urine. Keep in mind that in the summers, salt content in urine is especially high because humans sweat, and that sweating (which in general is tough on the heart muscle) drives out more water than salt and increases the salinity of the blood (if sweat were pure water, the problem would be much worse).

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      • miriam says:

        It is not clear why salt increases blood pressure. It does not seem to be a problem for every person, but if you reduce salt intake in a population you will see an effect from the people it does work in.
        For example, it is not clear why diuretics reduce blood pressure in the long term (hint: it is not about dehydration).
        I think the interesting work would be WHY a reduction in salt reduces blood pressure (especially in the long term, where you would expect it not to be a problem of fluid balance) and WHICH individuals it is effective in. A freakogenomics, if you will.
        I fear that line of research will not be popular…

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  7. Ted Pavlic says:

    So, from this little blurb, it appears like you’re saying the body’s ability to osmoregulate is hampered by the lack of salt availability? That is, as urine is the natural mechanism for osmoregulation in mammals (with perhaps sweat playing a role in less hairy mammals like humans), the suggestion seems to be that urine should do a good job balancing salinity (and thus blood pressure), but it can only UPregulate to the appropriate salinity (preventing low blood pressure) if salt is available.

    So it may suggest that having a little extra salt isn’t a bad thing (surely the body’s ability to osmoregulate with urine is limited on the other end though — there must be some limit to salt intake that wrecks things).

    Other studies (e.g., Simpson, Sword, Lorch, and Couzin (2006) in PNAS) suggest invertebrates do a good job balancing salt intake on their own if provided rich enough sources. It seems like that work could be incorporated here too. Right?

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  8. Gary says:

    You need salt to survive. The average person has to have 1/2 Lb. in their bodies at all times. No salt in your body 100% fatal.

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