Fact or Myth: Sodium Raises Blood Pressure

Scott 35
Matt asks: Why does salt raise blood pressure?

eat-less-salt2
Well, Matt, it turns out a high sodium diet might not raise blood pressure, nor have any sort of adverse effect on cardiovascular health at all.  But I’ll cover the theory on why salt raises blood pressure below- just realize it is just a theory and one not backed up by much of any hard scientific evidence (and there is more evidence that says it doesn’t than does).

The debate over eating too much salt has been around since the 1960s. Almost every major governmental health organization embraces the idea that eating too much salt is damaging to your health. Most major news outlets report on these recommendations and people tend to try and follow them. This is most likely why most of us, especially the elderly with heart problems, know to reduce the amount of salt we eat. Those of us who like the idea that any recommendation be backed up by solid evidence, have to step back on this one. As stated, currently there is no solid evidence that salt will chronically raise your blood pressure. Yes, none.

So why have most health organizations pushed the idea of low sodium diets? The theory behind their supposition is sound, and there are some studies that show a minor risk of elevated blood pressure with extremely high salt intake. Unfortunately, there are many other studies that show no increase, and still some that show reducing salt intake might actually raise your blood pressure! Let’s look at the controversy in more detail.

The idea salt will increase your blood pressure has to do with osmotic pressure. Osmosis is the movement of a solvent (in this case water) across semi-permeable membranes (like cell walls), from areas of lower solute concentration (in this case salt) to areas of higher solute concentration. This naturally equalizes the solute concentration on both sides of the membrane. (This osmotic pressure is also why salt can be used to preserves meat.)

So the theory goes that when we eat too much salt, our bloodstream has more sodium in it than the surrounding areas of our body. This causes the water in those areas to be pulled into our bloodstream. The increase in water within the arteries and veins causes an increase in the pressure within those arteries and veins. The salt itself also acts like an irritant within the arteries causing them to constrict. This too is thought to increase your blood pressure.

The theory seems, on the surface, very sound. After all, we can make the process of salt pulling water through membranes happen time and time again in the lab. The question is, does this actually happen within our bodies, and does this actually cause long term hypertension (high blood pressure)?

In 1969, Lewis Dahl testified before Sen. George McGovern’s “select committee on nutrition and human needs”. He was concerned about the high concentrations of sodium in baby foods and thought this might cause increase in people’s blood pressure long term. His reasoning was that studies done on rats showed increases in the blood pressure of the rats.

The conversation about salt and hypertension began to circulate among health organizations. The National Institutes of Health, in 1972, began introducing “High Blood Pressure Education Programs”. As their evidence, they pointed out observationally, populations who ate very little sodium had low incidents of high blood pressure. They also pointed to the rat modeling. Scientists at the time questioned this, as the rat studies had them eating 60 times what the average person does. They also pointed out the populations who ate low sodium diets, also ate low amounts of other things, like sugar (which also affects osmosis).

Despite their objections, publicly, the idea of high sodium diets causing high blood pressure was here to stay, and remains today. The Centers For Disease Control, The National Institutes of Health, The American Heart Association, and many other organizations currently promote low sodium diets.

Despite the seemingly unified front presented by these distinguished organizations, the controversy among scientists is extremely heated. In 1998, award winning author Taubes, published “The Political Science of Salt” in the Journal of Science. He stated, “The controversy over the benefits, if any, of salt reduction now constitutes one of the longest running most vitriolic and surreal disputes in all of medicine.”

One surgeon general in a report wrote, the speed with which US federal agencies embraced sodium reduction, “stood in stark contrast to how long it had taken for recommendations to emerge on the importance of reducing blood cholesterol levels”. He also noted that the difference was even more remarkable considering the absence of published research that actually tested the theory. On the flip-side, Sir Micheal Rawlings, the chair of the National Institute for Health and Clinical Excellence, who promotes salt reduction diets argued that, “Guidance (in policy making) is based on the best available evidence. The evidence may not, however, be very good and is rarely complete.” Not a very strong argument for reducing salt intake.

Let’s look at a few relatively recent studies. In 2008, Italian researchers began publishing the results from a series of clinical trials, all of which reported that, among patients with heart failure, reducing salt consumption increased the risk of death. These studies were followed by others which showed among Type 1 and 2 diabetics, healthy Europeans and patients with chronic heart failure, those that ate salt at the lower limit of the normal range were more likely to have heart disease than those who ate salt in the middle range of normal.

In 2011, two Cochrane reviews found no evidence that low salt diets either improved or worsened peoples’ health. They stated, “After more than 150 random clinical trials and 13 population studies without and obvious signal in favor of sodium reduction, another position could be to accept that such a signal may not exist.”

Even in the face of no clear scientific evidence to support it and some to the contrary, in 2010 the Centers for Disease Control and Prevention, the Institute of Medicine, and the American Society of Hypertension all continued to promote low sodium diets as a means of controlling high blood pressure.

In the end, being a medical professional and someone who needs clear evidence to make a decision about whether I get to add copious amounts of salt on my fries, I am pleased to find that so far there is very little! All the major health organizations seem to promote low sodium diets, but none have actually published consistent studies that show low sodium diets help in health, particularly not in cardiovascular health. What I find most annoying, a pet peeve of mine, is that none of these organizations tell people that the science behind their policies is controversial and they might be flat wrong. Ronald Bayer, David Merritt Johns, and Sandro Galea said it best in their article “Salt And Public Health”- “After a careful consideration of the debate over salt, we have concluded that the concealment of scientific uncertainty is a mistake that serves neither the ends of science nor good policy.”

So you should you go out and smother everything in salt now? As with most things, if science hasn’t been able to answer the question definitively one way or the other, and you want to be safe rather than sorry, just go with the age old rule of “moderation in everything”.  If you, like me, like to salt everything like the rim of a margarita glass and moderation be damned, at least now you can feel a little better about it as science seems to be leaning more and more towards low sodium diets being unnecessary and high sodium ones not being harmful at all.

If you liked this article and the Bonus Facts below, you might also like:

Bonus Facts:

  • High blood pressure is neither a disease nor an illness in and of itself. It’s merely a risk factor for other problems. For instance, if you have chronic high blood pressure, your risk of having a heart attack or stroke goes up significantly. This high pressure could be caused by excessive plaque on the inside of your artery walls, making those arteries in effect, smaller. Think plumbing. When the pipes that transport fluid get smaller, the pressure that same volume of fluid exerts goes up. What happens if your blood pressure gets too high? I’ll answer that question with another one. What happens if the water pressure in your houses pipes gets too high? Your pipes burst. Same thing here. Should your blood pressure get too high, your arteries have a greater chance of bursting. If there is too much gunk inside your pipes (plaque inside your arteries), that ball of gunk could get too big and clog off your pipes! Seems bad too me! Especially, if those arteries are in your brain, or heart. It’s not like kidneys, where you have two! You spring a leak in those organs, and your family finally gets that big paycheck from your life insurance policy! Not really the best way to get paid, well, unless you’re really a jerk and everyone in your family hates you!  Then they might not mind so much, but you certainly would.
  • Blood pressure is measured in millimeters of mercury. For reference, 1 psi (pounds per square inch) is equal to 51.7149326 millimeters of mercury. If you were bleeding and wanted to stop the blood-loss with direct pressure, and you should, you would only need to use about 3 psi to stop it. Unless they have really high blood pressure, then maybe 4 psi. Basic math saves the day again!
  • The first known experiment to measure the exact pressure of blood was performed by Stephen Hales on December 1, 1733. He took a live horse. Attached a tube to her left crural artery, then allowed her blood to rush through the tube and it rose to a height of 8’3”. He noted that “when it was at its full height, it would rise and fall at and after each pulse 2, 3,or 4 inches”. Yes the horse bled out, but don’t think Mr. Hales was too cruel, he performed the experiment on a horse that was about to be put down anyway!  To the horse, I’m sure this distinction didn’t matter much of course. :-)

*Legal Disclaimer: While I am a medical professional, this article contains general information about medical conditions and treatments. The information is not direct advice for your specific situation, and should not be treated as such. You should never delay seeking medical advice, disregard medical advice, or discontinue medical treatment because of information in this article…. There, I’ve covered myself.  ;-)

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35 Comments »

  1. Ian Wardell June 12, 2013 at 12:02 pm - Reply

    I’m getting more and more convinced that salt does significantly increase my BP. Whenever I eat crisps (chips if you live in the USA) which have a fairly large amount of salt, my BP goes up significantly the next few days.

    I tried getting saltless crisps about a week ago and added my own “lo-salt” (a salt substitute consisting of potassium chloride and sodium chloride (salt), but twice as much as the former than the latter).

    Anyway the lo-salt flavoured crisps (chips) diodn’t raise my BP at all.

    OK I know that further experiments on myself is required. But at the moment I’m strongly suspecting salt as the culprit. I’m also suspect that sugar increases my BP too. But lots of investigation required to establish that!

    Ian

    • lisa August 18, 2013 at 5:05 pm - Reply

      Maybe you have a poor potassium to sodium balance. My mum has hypertension and was on a low sodium diet but she was not getting enough potassium and her blood pressure was not stable. If you are concerned you may want to have your blood potassium level checked.

      Now that she is consuming enough potassium she her blood pressure has been normal for over a year while consuming sodium within normal ranges(more than 2500 mg)

  2. Yanike June 28, 2013 at 8:26 pm - Reply

    Salt (Sodium) DOES raise your blood pressure. I went to the doctor and my blood pressure was 130/90. She told me to control my salt (sodium 1500mg limit) and I had a check up two days later with my blood pressure 108/87. Anytime I eat lots of salty foods, I get a spike in my pressure. I am definitely salt sensitive.

    SALT (SODIUM) DOES affect your blood pressure. You have to be careful (it sneaks up on you good) and adjust your diet to limit sodium intake and watch for signs of your pressure raising. Especially when your body behavior changes.

    Work out as well! If you are lazy or not that active, take 30 minute walks 5 days a week (150 minutes total) minimum to get a decent exercise.

    • lisa August 18, 2013 at 5:27 pm - Reply

      I think the point is that recommending a lower sodium diet, that maybe affects a specific set of people, those who already have hypertension and are salt sensitive, to an entire population is ridiculous. Another point is whether high salt intake leads to chronic cardiovascular problems, which is being touted as fact to the public but has no research to back it up. I consume way more sodium than the CDC recommends and my BP has never been higher than 117/70, my highest ever, normal about 100-110/65-70. Neither of our cases prove one way or the other the effects “high” sodium intake has on the general population.

  3. Yanike June 28, 2013 at 8:37 pm - Reply

    As for Sugar, women should limit their sugar (Total Carbs is what matters and watch out for certain sugar alcohols) 20g-30g a snack and 30g-45g each meal. Men should keep their snack the same as women 20g-30g a snack and 60g – 75g a meal. The lowest numbers are the lmit for diabetics of course.

  4. whakers July 24, 2013 at 12:32 pm - Reply

    I believe that some people have a sensitivity to sodium. I’m convinced that I do. After being on 3 different BP meds at one time and still having uncontrolled hypertension, I started reading food labels and drastically reducing my sodium intake. Most processed foods are loaded with sodium. I have been able to stop 2 meds completely and reduce the third one to 1/4 the prescribed dosage. For me, reducing sodium has made a huge difference. Last night I took 10 mg of lisinopril, which is 1/4 of the prescribed daily dosage. Today my BP is too low, 105/48. I really have to consistently monitor it, as low BP isn’t much fun, either.

  5. John Verrilli August 22, 2013 at 9:41 am - Reply

    Yea, whatever. Believe what you want. I have been reading health books for years….DECADES…and I’ve have read in them EXACTLY what is printed in this article. There NEVER has been a proven link between salt and high blood pressure. Furthermore, in one of books it pointed out that salt is used to make stomach acid, and it’s ironic that as we age, the low sodium diet so often touted leads to digestive problems.

    Keep believing doctors who take 3 credits of Nutrition in college and pitch compounds that cause worse side effects than the actual disease.

    Doctors, who say Chiropractic is “not real medicine.” Read the Winsdor papers. A doctor who set out to prove Chiro was fake by doing autopsies found that 99 out of 100 organ failures were due to lack of nerve energy caused by “subluxations” which pinch the nerves and interrupt nerve energy flow. (I’m not a chiropractor).

    Go read books by Norman Walker, (especially “Fresh Fruits and Vegetables.”), TC Fry, and Herbert M. Shelton (Superior Nutrition, Fasting can save your life). I’ve read them all.

    BOTTOM LINE this is an excellent article and I’m actually surprised to see the truth so openly posted in an article like this…but you believe what you want & take chemicals pushed by the medical profession…eat what you want, drink what you want, don’t exercise and when things go wrong just take a pill….

    • Alan December 12, 2014 at 2:19 am - Reply

      I attempted to look up these “Winsdor Papers” and even Google doesn’t know what you are talking about. If you really want to win people over, you should actually post links to the information you want us to read.

  6. marco February 27, 2014 at 5:01 am - Reply

    Guys you all are missing one point: sodium is poisonous to us. Even if does not raise BP, its still poison ;/ not good at all

    • Daven Hiskey
      Daven Hiskey February 27, 2014 at 2:13 pm - Reply

      @Marco: You would die instantly without sodium in your body.

    • Marco February 27, 2014 at 3:01 pm - Reply

      I am not the same Marco as Mr. “Salt is poison”. Just to be clear

      • Daven Hiskey
        Daven Hiskey February 27, 2014 at 3:23 pm - Reply

        Ha, noted!

  7. Mike February 27, 2014 at 5:07 am - Reply

    This article is misleading. Just because salt’s negative effect on blood pressure is a “theory” doesn’t mean we should ignore it. In fact most of medicine and science is carried out on plausible theories. The truth is a low salt diet is less harmful than a high salt diet and like all things the real moral of the story is moderation. Also this author contradicts themselves by saying there is “no evidence… Yes none” to support this theory, but then goes on to cite at least one study that shows the negative corrolatuon in humans and another involving rats. That’s evidence, at least some not none. Most of medicine is black magic and many doctors will admit that. Sure sometimes we are far from knowing but in this case there’s enough science behind salts impact on BP to make it worth considering. Also remember the human consumption of high salt quantities is a fairly new thing on the evolutionary scale, so it’s impact on our bodies is fairly unnatural.

    • Daven Hiskey
      Daven Hiskey February 27, 2014 at 2:13 pm - Reply

      @Mike: “No evidence… Yes none” I think Scott is meaning “No reputable evidence” Or, rather, “No evidence that is not flawed.”
      .
      “Everything in moderation” Yep, exactly. As Scott is fond of saying, “Even water will kill you in high enough doses.” He even once told me a story of a woman he attempted to treat for this very thing- she drank massive amounts of water and ended up dying from it.
      .
      “Most of medicine is black magic and many doctors will admit that.” I don’t think any doctors would ever say that. Maybe a century or two ago. But there is an amazing amount of good science involved here these days. We are far from knowing everything, but it’s certainly not black magic or just guess work, as that would seem to imply.

    • Marco February 27, 2014 at 2:45 pm - Reply

      I suggest you read the book “Salt”. It is mostly a geopolitical historical account of salt in our civilization, but it also has a good deal of science in it. We built our civilization on salt.

  8. George Vieira February 27, 2014 at 5:58 am - Reply

    The first paragraph says ” just realize it is just a theory and one not backed up by much of any hard scientific evidence,” I believe that since this is a scientific minded website it shouldn’t use the word theory in this context, since in science, a theory is an accepted explanation of a phenomenon, proven by testing.

    • Jack April 7, 2014 at 6:33 am - Reply

      Yeah, he should have used hypothesis. I’m going to have to look up the history of theory and see if anyone knows how it ended up with two such different meanings.

  9. Mark February 27, 2014 at 7:49 am - Reply

    For a medical professional (which leads to an assumption of advanced education), you have a horrible grasp of grammar and spelling. This discredits much of what you say, in my mind. Having someone else review your work before publishing would go a long way.

    I will continue to listen to my cardiologist on this matter and limit my salt intake.

    • Daven Hiskey
      Daven Hiskey February 27, 2014 at 1:56 pm - Reply

      @Mark: Something you’ll find seemingly true about a large number of medical professionals, the stereotype of their handwriting being horrible is generally correct. (Scott’s is particularly bad.) And their technical writing can also sometimes be particularly terrible, pre-edit. (They study medicine and the human body, not writing, after all) But, in over 100+ articles Scott has written, he has never been shown to be wrong on a main point (and only a few cases of being wrong on a minor point). Typos? Awkward sentence? You will always find at least one of these in each of his articles, despite my sincerest efforts to get rid of them all. But in the end, I care about accuracy much more than grammar. Both would be good, but finding a writer of Scott’s particular expertise and ability to think critical and process vast amounts of medical knowledge is extremely difficult. These people aren’t a dime a dozen. :-)
      .
      But really, the strength of Scott’s arguments are never based on his extensive medical knowledge. That just helps him thoroughly vet the various studies on the subject where most would get lost in the terminology, let alone be able to think critically about them and their methodology. The strength of the argument is the studies themselves. In this one, you’d do well to actually read the two Cochrane reviews, and perhaps forward them to your cardiologist for his/her thoughts.
      .
      Don’t be surprised if he/she has already ready them though, and maybe even agrees with them. What doctors tell their patients doesn’t always line up with what they actually know or believe to be true. Particularly in cases like this where lawsuits may be a very real possibility if they told you to eat all the salt you wanted, then you died of a heart issue (but having nothing to do with the salt), then your family sues them and cites what various government agencies say on the subject, rather than what the medical world actually thinks. :-) Watching your sodium isn’t likely to hurt either, but covers the cardiologists’ backside. (I actually had an interesting discussion about this with Scott just last night about a doctor he was discussing this with who said something very similar as to why despite that he knows sodium isn’t going to be harmful in this way, he still tells certain of his patients to watch their sodium intake.)
      .
      In the end, as I always say, “Question everything,” but also when questioning, do the research to find the answers too, and then double check that research just to make sure. :-) And, maybe don’t make the mistake of equating grammar and writing ability with knowledge of a subject or intelligence. I’ve worked with a ton of writers. I can say, journalists (and other such people with a writing background) are great at writing… They almost all are horrid at research, which surprised me on the journalists, but maybe explains a lot about the state of media reporting on scientific studies. Funny enough, the best combo of writing ability and research seems to be lawyers. They are phenomenal at both in my experience. Scientists, or people with a science background, tend to be poor at writing, but incredible at research and critical thinking. Of course, that’s only going with a sample-size of a few dozen writers I’ve worked with, and there is one exception I’ve found in that, but it’s a trend I’ve observed.

  10. Marco February 27, 2014 at 12:20 pm - Reply

    I was wondering if I could ask the author of this article for a small favor.
    At the beginning I read this sentence in regard to salt intake:

    “But I’ll cover the theory on why salt raises blood pressure below- just realize [it is just a theory] and one not backed up by much of any hard scientific evidence…”

    Here you are using “Theory” in its popular parlance. WHich is fine and all. The problem is that this is a scientific related article and when a theory is not supported by evidence we call it a “Hypothesis”.

    Those of us that write in the scientific realm should make an effort to make this distinction, mostly because the next time I get some Young Earth Creationist telling me evolution is “just a theory” I swear I am going to start jumping up and down like a Chimpanzee and make backward sammerault. Then I’ll throw feces at him/her.

    I am sure you don’t want such a scene to become reality. Heck, you probably don’t want to think it up in your mind.

    So let’s start a campaign to call a Theory a “a coherent group of tested general propositions, commonly regarded as correct, that can be used as principles of explanation and prediction for a class of phenomena” and call anything that is meant to be pulled from one’s rear orifice an “Hypothesis”.

    BTW: I know the dictionary return both meanings. FOr the sake of Science, let’s change the meaning back since we already have a good working word for “I just pulled this out of my ass”.

    • Daven Hiskey
      Daven Hiskey February 27, 2014 at 1:32 pm - Reply

      @Marco: That’s a good point. I’ll start working that distinction in to future articles. :-)

  11. John Fischer February 27, 2014 at 12:36 pm - Reply

    Not a single legitimate conclusion can be drawn from a single blood pressure measurement. BP varies widely even from moment to moment. I have many times seen 160/100 drop to 130/75 over the course of a few minutes. As well, BP measuring equipment is highly variable and susceptible to wide variations from things like cuff size and user variations.

    Any conclusions drawn from a few measurements are nothing more than speculation and wishful thinking.

  12. Michael Stelly March 2, 2014 at 7:02 am - Reply

    First, this is not a peer-reviewed journal article. I agree, the correct use of “theory” has been obfuscated by the colloquial “just a hunch” version. But, let’s move on, ok?

    I don’t get that the article is in the least bit misleading. I do get that the author makes the point that apparently is lost on many — “As stated, currently there is no solid evidence that salt will chronically raise your blood pressure. Yes, none.”

    He also mentions to think critically. So, if you don’t believe him, a) continue with your belief, or b) find out for yourself. Do the legwork. Read the articles. Now you have a starting point. Thank him for that.

    In my opinion, focusing on the occasional grammatical error or “theory vs. hunch” debate unnecessarily diminishes the author’s intent. My takeaway is that this article helps challenge my assumptions about what I thought was already scientifically concluded. I learned something. That’s the point.

    • Marco March 3, 2014 at 2:05 pm - Reply

      @Michael Stelly I am not sure if you were referring specifically to my post in regard to the usage of “theory”, but I assure you that my comment was not intended to criticize the writer at all. At least not in the same terms as a grammatical or spelling “error”.

      My comment is not about an “error” rather it is a suggestion that those of us that read and write about science do our part to reclaim the usage of the word “theory” from the mainstream or that at least we try.

      There are those that comment on obvious spelling errors and I agree they are not important in the context of the information provided in the article (although I agree they can be distracting and I am speaking from a non native English speaker), but unless their number and character is such that they make understanding the article difficult or even impossible, you won’t find me posting about them.

      The word “theory” on the other hand is a word that is being actively used by certain factions of the science / religion discussion to discount 200 years of scientific advancement and it is being actively used to mislead children into discounting science as a whole.

      If you have watched the Nye – Ham debate, Gawker asked some creationists to write a question to evolution supporters on a piece of paper and they published these questions in the form of pictures. Invariably the “it’s just a theory” question appeared.

      It’s in that spirit that I have asked the curators of this website to try to use the word in its scientific meaning. If we in the science and technical fields don’t do that, we cannot expect those that want to distort science for their objectives to do it on their own.

      So, with all due respect, I won’t take your advice. I will certainly let slide silly spelling errors but this is important to me and it should be important to all of us that love science.

  13. Alan December 12, 2014 at 2:11 am - Reply

    One fact I would like to add:

    Thiazide and thiazide-like diuretics are another piece of evidence in this controversy. Interestingly, thiazides are called diuretics but when taken daily this diuretic effect becomes almost zero. After a period of chronic thiazide therapy, the primary benefit these medications provide is that they increase the elimination of sodium and chloride ions from the blood by way of the Na/Cl symporter in the distal convoluted tubule (along with other effects such as retention of calcium). Despite losing the diuretic effect thiazides retain their blood pressure lowering effects long-term and are one of the medications used first line for lowering blood pressure. This lowering effect is generally attributed to the elimination of sodium and seems to be in line with the idea that high sodium levels do increase blood pressure.

  14. Gino December 12, 2014 at 8:08 pm - Reply

    Believe it or not. Salt appears to lower my BP. If I eat too many chips I actually get dizzy from low BP. Can’t say I get it.

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