A low salt diet for high blood pressure: Where’s the evidence?

A low salt diet for high blood pressure: Wheres the evidence?

We know that people with high cholesterol have a higher risk for strokes and heart attacks than people with low cholesterol. So if a medicine lowers cholesterol it should also lower the frequency of strokes and heart attacks too. Right? Not necessarily.

Estrogen lowers cholesterol and doesn’t lower stroke or heart attack risk. We also know that people with high blood pressure have a higher risk for strokes and heart attacks. Does that mean that a food that elevates blood pressure increases stroke and heart attack risk? Again, not necessarily.

The confusion here is a misunderstanding of the difference between clinical outcomes and intermediate outcomes. A clinical outcome is something that a patient notices herself and that impacts her life directly, like a stroke, a heart attack, or a bone fracture. An intermediate outcome is something that is measured by the doctor and that doesn’t cause symptoms directly, for example, elevated blood pressure, elevated cholesterol, or low bone density. Intermediate outcomes can be risk factors for clinical outcomes but shouldn’t be confused with them.

What does this have to do with salt?

Lots of evidence shows that eating more salt raises blood pressure, so doctors have always made the assumption that eating more salt also increases the risk of strokes and heart attacks. But as we’ve seen with estrogen and many other examples, guessing the effects on clinical outcomes from intermediate outcomes is frequently incorrect.

In 2005, the U.S. Department of Agriculture and Department of Health and Human Services wanted to revise their dietary recommendations for salt intake. Given the very little scientific evidence they had, what they did was both simple and presumptuous. They knew that 1,500 mg of sodium intake daily was the minimum needed for adequate nutrition. They also knew that at daily intake levels above 2,300 mg of sodium (which is about a teaspoon of salt) blood pressure begins to increase. So the U.S. recommendations since 2005 have been that everyone should eat no more than 2,300 mg of sodium daily, and that people at very high risk of stroke and heart attack should ingest no more than 1,500 mg.

How are we doing? Well, on average Americans ingest 3,400 mg of sodium daily, well above the recommendations. A host of policy initiatives has been spawned by the recommendations in an effort to educate consumers, clarify food labels and coerce restaurants to lower sodium.

But did anyone test the effects on the clinical endpoints?

The Institute of Medicine (IOM) was commissioned to review all the studies relating to the health effects of sodium intake. Their report (which is over 150 pages) was released recently. A major conclusion of the IOM paper is that the quality of the current evidence linking salt to health outcomes is very poor. There are virtually no randomized studies and the rest of the studies suffer from important methodological flaws (like imprecisely measuring salt intake or using self-reported food diaries to estimate salt intake).

The surprising and worrisome finding was that some of the randomized trials actually found worse outcomes with very low salt intakes. This isn’t as preposterous as it may sound. We have no solid understanding on salt’s effect on the body beyond that on blood pressure, so there could be many mechanisms that could explain worse cardiovascular outcomes with a very low salt diet.

The IOM endorsed the current belief that there is very likely a quantity of daily salt intake above which the risk of cardiovascular disease increases. The current evidence is simply insufficient to figure out what that limit is.

I’m always impressed when science comes up with the answer, “We have no idea,” because that’s very likely to be honest. Those who are more committed to enacting policy than to figuring out the truth are less likely to confess ignorance and to wait for better studies before making up their minds. The American Heart Association issued a press report criticizing the IOM paper and arguing essentially, “But salt increases blood pressure!” which no one disputes.

So for now add me to the list of salt agnostics. I frequently ask patients to cut down on salt in the short term to avoid fluid retention, for example when traveling. But we should have the honesty to admit that in terms of long term outcomes we don’t know how much salt is too much.

And if you’re not going to eat that pickle, can I have it?

Albert Fuchs is an internal medicine physician who blogs at his self-titled site, Albert Fuchs, MD.

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  • Chiked

    So how in the world do you explain my mum. When she eats a lot of salty foods, she retains water and her bp goes up. Give her her water pill and the swelling decreases and bp goes down.

    • Albert Fuchs

      Salt definitely causes water retention and increases blood pressure. The study I posted about had to do with whether it also increases the risk of stroke and heart attacks.

      • Dorothygreen

        This is confusing. The title of this article is A low salt diet for high blood pressure: where’s the evidence?. And then you say Salt definitely causes water retention and increased blood pressure but the study I posted had to doe with whether it also increases the risk of stroke and heart attacks.

        But aside from that why does eating all the salt one wants make any sense. Humans never had this in their diet in such large amounts – got it from plants and seafood and it seems from those who study indigenous cultures, as low as 500 mg a day. .

        And then there’s the addictive property of salt, just like sugar and fat – make us eat more. Take a look at what America is eating. Spend a few hours in the average American grocery store or a “food desert” corner Bodega. Check out the sodium content, You will find how easy it is in America for a poor person to consume 5 to 7 Gm of sodium (not salt) in a day and less than 3 Gm of potassium.

        What about the Japanese who had very high sodium intake which correlated to a high rate of stroke. Seems to have decreased with their campaign.

        But still researches and even Med page use headings like this and it does led folks to then say “hey, I don’t have to cut my sodium” and nothing, nothing is done about the root causes of our poverty, obesity, sugar addiction, high prevalence of chronic preventable diseases and extraordinary health care costs.

  • Suzi Q 38

    I have had HBP since I was 27. I miss pepperoni pizza the most.

    • Albert Fuchs

      Ask your doctor. Maybe you can still enjoy it as a rare treat. You’re young. Whatever diet you stick to has to be sustainable. It can’t feel like a punishment.

    • Suzi Q 38

      Thank you doctor. I just ate a few pieces last weekend.
      It was my aunt’s 100TH birthday. I ate that AND the Italian rum cake. I am not young. I am 57. I have had HBP controlled with BP meds since I was 27.

  • medicricci

    Love the post, especially your elegant quote about the desire to make policy outstripping the evidence. I did a small paper on the role of postassium (vis-a-vis sodium/chloride) using a lot of work by Frassetto. I have seen outstanding results, even in familial hypertension simply by boosts in potassium & magnesium intake. It appears the sodium factor is just that, a factor. Plenty of research points ratios of chloride, magnesium and potassium (we’re largely very undersourced on the latter two), but ratios involve critical thinking and are therefore unsuitable for simplistic black-n-white policy initiatives designed for the general public.

    • Albert Fuchs

      Thanks for the praise!

  • M. Miller, RD, CSG, LD

    HA and double HA! As an RD with 30+ years of experience, when the 1500 mg recommendation for Na came out, I told anyone who would listen that it was just plain stupid and unobtainable as a general public (everyone over 50) recommendation. It made me angry when the media and even medical professionals would say that no improvement has been made by the public and manufacturers in sodium intake in the last 20 years. Fact: Nutrition books published in 1976 stated average sodium intake in the US as 5000-7000 mg, a no added salt diet as 3000-4000mg, a low sodium diet 2000 mg and below that a very low sodium diet. Hospitals and patient education materials still follow these designations for definition and education of NAS and low sodium diets. The current average intake in the US is 3400-3800mg. Math is not my strongest skill but even I can figure out without a calculator that this is an improvement- a MINIMUM of a 24% decrease. I think that would meet standards for statistical significance. As for manufacturers, while improvement is still needed, many items like tv dinners and soup that had 1200- 3500mg sodium per serving in the 70′s have half of that now. They have had to retrain consumers taste buds slowly. Yes, more couldn be done. As an FYI, to decrease sodium intake below 2000 mg means no bread or bakery products or a limited amount of SF bread (not readily available, expensive and not worth eating) limited meat and dairy because of naturally occuring sodium and a very long list of nevers with a short list of what you can have. Vegetarians don’t have it any better because soybean products are loaded with sodium and beans cooked without any salt defy blandness. To stay alive with liver failure or kidney failure or CHF – worth it. Just because the government thinks it would be a good idea- NEVER! What happened to public education and common sense?

    • Albert Fuchs

      Thanks for your informed and passionate comment. I totally agree.

  • Chiked

    This is what is wrong with medicine today. Should you really be telling your patients that we don’t know enough about the effects of salt? I mean if you agree that it can raise your blood pressure. Isn’t that enough of a reason to pass on that pickle?

    I get the sense that doctors have sold out to the pharmaceutical and food industries.

  • Independent in NY

    Salt in diet did make a difference with me, but I was later found to have Conn’s syndrome which caused elevated bp due to excess aldosterone and low serum K+….since surgery I can tolerate salt without consequence. Too many doctors know little to nothing about Primary Aldosteronism, it took me over 10 yrs of uncontrolled HTN, changing meds multiple times and reacting poorly to them, then developing low serum K dismissed as an “error” in lab tests. Then when it took 80 meq of oral potassium and a DASH diet to keep my serum K at normal levels I was accused by a provider that “you must be purging”….I walked around with a BP of 210/120 at times….It is said that about 1% of treatment resistant hypertensives might have PA but some literature says more like 15 to 20 %….would be worth looking into for anyone showing salt sensitivity

  • jere14

    As a patient who also had slightly high blood pressure, the hospital without my consent puts me on a sodium restricted diet. I am a fairly large person so the consequence was that they had to restrict my calorie intake to stay under the sodium limit. They kept me hungry for some ideal of health that is hardly even understood or proven. I think that was very bad policy on the hospitals part. This whole optimal nutrition thing has gotten out of hand.

  • Mickey7

    Diuretics are a staple of hypertension therapy which can also result in electrolyte imbalance. I have been treated for essential hypertension since I was 12 years old–early onset hypertension appears to run in our family–and consistently have a low sodium level. Further reducing it by cutting out salt never made much sense to me, as electrolyte imbalances can be far more dangerous than a chronic issue with hypertension. I think this another example of turning risk factors into diseases and creating more problems from the treatment than you would have from the condition itself.

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