Home > Uncategorized > Phantom epidemic: salt intake hasn’t changed in 50 years

Phantom epidemic: salt intake hasn’t changed in 50 years

October 27th, 2010

One of the health topics I’ve been curious about recently is the question of salt intake. It seems that everyone — governments, scientists, heart institutes — agrees that we eat way too much salt, and it’s leading to an epidemic of hypertension.

But there are skeptical voices — the much-maligned Gary Taubes is one, but there are many others (like my wife!) who argue that (a) sodium levels in the body are very tightly regulated, so any excess in a healthy individual is simply excreted out in the urine, and (b) dramatic reductions in salt produce only a minor blood pressure change of a few mmHg, and not in everyone, so blanket recommendations for the whole population to cut salt make little sense.

So I was interested to see a study from Walter Willett at Harvard in the current issue of the American Journal of Clinical Nutrition (full text here). He and a colleague reviewed studies between 1957 and 2003 that measured sodium excretion in urine — a very accurate way of determining salt intake that gets around the difficulties in figuring out exactly how much salt is in your food. They found two main things: (a) sodium intake averaged about 3,700 mg per person per day, which is way higher than the upper recommended limit of 2,300; and (b) it essentially hasn’t changed in the half-century studied.

Interestingly, these results agree almost exactly with similar reviews of studies from 33 different countries: salt intake is high, and it hasn’t changed in recent memory.

Now, here’s the question that Willett dances around in his discussion: If hypertension is a rising epidemic in the U.S. (and elsewhere), and if salt intake hasn’t changed in 50 years, how can salt possibly be the culprit? He points out that hypertension has “multiple etiologic factors,” and suggests that obesity may be a more important determinant.

The article is accompanied by a fairly strident editorial by David McCarron titled “Science trumps politics: urinary sodium data challenge US dietary sodium guidelines” (full text here). McCarron is a familiar figure in the salt wars, and is often maligned because he has consulted with the Salt Institute in the past. Lots of money sloshing around in this debate. What’s so interesting about this study is the involvement of Willett, a public health titan who normally lines up on the other side. Here’s what Willett had to say in a debate about New York City’s proposed salt rules on the New York Times website earlier this year:

The evidence is solid, based on many years of research, that reducing sodium intake from the high amounts now consumed in the U.S. will reduce the risks of these conditions [hypertension, stroke, heart disease].

His own study now tells us that the amounts now consumed in the U.S. are not at all “high,” historically speaking. Will this lead him to change his views? I’m not counting on it — but it’s at least encouraging that he’s interested in looking at the data.

  1. Monisha
    October 27th, 2010 at 16:07 | #1

    This is super interesting, esp as salt makes many healthy, but less palatable (e.g., bitter or strong-tasting) foods much more palatable. I’d always thought that rising sodium intake was attributable to processed foods, but the stability of intakes over time and across different places to me definitely implies rethinking the ‘daily limit’…

  2. Phil Koop
    October 27th, 2010 at 16:47 | #2

    Aha! And what about the claimed reason for our supposed increase in sodium uptake? That attributed to increased consumption of processed food. What can we say about the cause now that the effect has been debunked? Was this “fact” merely an unproven assertion all along? Either processed food is not in fact saltier than home-cooked, or we do not eat as much of it as claimed, or else we reduce sodium intake from other sources to compensate.

    The whole thing reminds me of the fluid intake wars. Until the science on the subject gets a lot more convincing, I think I’ll continue to do what I always do: drink when I’m thirsty, eat salt when I’m hungry for salt. As matters stand I’ll bet on evolution over science.

  3. October 27th, 2010 at 17:32 | #3

    I wonder if salt intake was actually higher before the advent of modern refrigeration. To keep stuff from spoiling you had to add a lot of salt, right?

  4. alex
    October 27th, 2010 at 21:34 | #4

    Thanks for the comments, Monisha, Phil and David. All three of you raise an interesting point about the supposed evils of salt in processed food. In his editorial, McCarron writes the following:

    “To the extent that caloric intake has been stable over populations and decades, so too has sodium. Thus, a potential benefit of reducing food sodium content would be a concurrent reduction of sodium. Working against that theoretical outcome, however, is the reality that over the millennia, before the introduction of processed foods, sodium was added to foods at the time of preservation, cooking, or consumption. An individual in our society has the identical options today as the food industry moves to offering more products whose ratio of calories to sodium is increased (ie, lower sodium content per serving). This individual choice could abrogate any effect on average sodium intake in society as these data indicate has happened.”

    In other words, he’s saying that yes, processed food now has more salt than it used to, BUT that doesn’t necessarily mean we’re eating more salt. Maybe 50 years ago, you ate baked potatoes — with a nice pat of salty butter. Now you eat salty french fries or potato chips, but you don’t add any extra salt. Ultimately, your taste buds make the calculation to ensure that you end up with roughly the right amount of salt to regulate “extracellular fluid volume.”

    I should add, of course, that I’m not advocating the carefree consumption of processed foods! But the bigger issue with those foods may be what they’re missing (nutrients, etc.) and other additives like preservatives, rather than the salt.

  5. Johnny
    October 28th, 2010 at 07:26 | #5

    I read an article about salt intake in the National Post earlier this year, luckily the NP has lowered their pay-wall: See

    “…none[salt intake studies] has ever shown, for example, that salt consumption increases overall death rates, or death rates from cardiovascular diseases, or from heart attack or from any other cause.

    On the other hand, studies do point to increased risk of heart attack and higher death rates among some individuals on low-salt diets…”

  6. Johnny
    October 28th, 2010 at 07:27 | #6

    Hmm – blog ate the URL – it’s network.nationalpost.com/NP/blogs/fullcomment/archive/2010/04/23/lawrence-solomon-savour-the-salt.aspx

  7. alex
    October 28th, 2010 at 11:01 | #7

    Thanks for the link, Johnny. Interesting stuff — and a good reminder that these doubts about conventional wisdom on salt aren’t new. In fact, Gary Taubes wrote about this stuff in Science over a decade ago.

    (I added the live link to your original comment, BTW.)

  8. October 28th, 2010 at 11:36 | #8

    What has changed in the last 50 years is the use of of drugs. Steroids, oestrogen/hormonal, anti-depressants etc.
    Is there a link with salt sensitivity/interaction?
    Read Maragaret Wilde’s website and blog.
    http://www.wildeaboutsteroids.co.uk/
    http://wildeaboutobesity.blogspot.com/
    She has some compelling arguments and many examples and facts.

  9. October 28th, 2010 at 12:44 | #9

    What has definitely increased enormously over the last 50 or 60 years is the volume of prescription drugs prescribed and taken. Many, perhaps even most, of these drugs cause relaxation of the muscles of the blood vessel walls, with sodium retention as a side-effect. This in turn leads to water retention because extra sodium/salt attracts water to itself. If the drugs are taken for long enough, the extra fluid in the body (salt water/fluid retention in the veins = extra blood volume) results both in higher blood pressure (because of the extra pressure on the walls of the blood vessels) and in weight gain. The blood vessel walls have become weakened and the kidney function impaired by the extra blood volume to have to deal with. A general term for this sort of problem (not always caused by prescription drugs) is salt sensitivity.

    I hope it is clear from what I have written that salt sensitivity is on the increase. The straightforward way for people who are sensitive to salt to reduce high blood pressure is to cut down drastically on intake of salt and salty food. This will also reduce some of the excess weight, because some of the excess salt water from the blood stream will be excreted in the urine.

    Unfortunately very few physicians explain to their patients, or even know properly themselves, that when prescribing these drugs that cause weight gain, e.g. most steroids, most anti-depressants, anti-psychotics, anti-epileptics, etc, patients should be warned not to eat salt or food containing salt while they are on the medication. If they were given this information and kept to it, the problems would not arise in the first place.

    If you click on the Obesity and the Salt Connection link on my website, you will be able to read my Mensa article on the subject.

  10. October 29th, 2010 at 14:20 | #10

    Interesting paper Alex. It’s especially interesting that the official conclusion of the paper (“Sodium intake in the US adult population appears to be well above current guidelines and does not appear to have decreased with time”) is quite different from the one you took, although they seem equally valid based on the the results.

    I’m not willing to throw out the sodium with the bathwater just yet, since systematic reviews (e.g. http://www.ncbi.nlm.nih.gov/pubmed/15266549) suggest that reducing sodium intake has a clinically significant impact on blood pressure in hypertensive individuals. Whether the biggest etiological factor in hypertension is sodium intake or something else like obesity seems like something that’s up for debate, but if you have high blood pressure, reducing salt intake still seems like one reasonable course of action.

    @ Margaret,

    How does relaxation of smooth muscle in the vasculature result in increased sodium retention? And also, if your blood vessel walls are more relaxed, won’t that *lower* blood pressure?

    Travis

  11. October 29th, 2010 at 17:30 | #11

    @ Travis

    The relaxed state of the blood vessel walls and the impaired kidney function permit a greater blood volume, i.e. it allows the incursion of more salt and its accompanying water. Possibly ‘relaxed’ is not the most appropriate word for me to use. – What I mean when I use that word is that the blood vessel walls are relaxed in the sense that they do not have their normal strength to resist the incursion of an extra volume of fluid. I saw the problem described as ‘relaxation’ once years ago and have continued to use that word as it seemed to fit with my own experience, but I no longer have a note of where I saw the word used in that way. (I’ve never understood or agreed with the usual claim that relaxation of the blood vessels lowers blood pressure. Maybe this is with people who are not sensitive to salt. – I don’t know.)

    Extract from http://www.mayoclinic.com/health/sodium/NU00284

    “Your kidneys naturally balance the amount of sodium stored in your body for optimal health. When your sodium levels are low, your kidneys essentially hold on to the sodium. When sodium levels are high, your kidneys excrete the excess in urine.

    But if for some reason your kidneys can’t eliminate enough sodium, the sodium starts to accumulate in your blood. Because sodium attracts and holds water, your blood volume increases. Increased blood volume makes your heart work harder to move more blood through your blood vessels, which increases pressure in your arteries. Such diseases as congestive heart failure, cirrhosis and chronic kidney disease can make it hard for your kidneys to keep sodium levels balanced.

    Some people’s bodies are more sensitive to the effects of sodium than are others. If you’re sodium sensitive, you retain sodium more easily, leading to fluid retention and increased blood pressure. The extra sodium can even lead to high blood pressure, which can lead to heart disease, stroke, kidney disease and congestive heart failure.”

    Although the Mayo Clinic mentions arteries rather than veins, people who are extremely sensitive to salt are far more aware of swollen veins and the problems and pain they cause, since the changes are very obvious and visible, rather than problems with arteries, even if these may be more dangerous than the vein problems.

    Margaret

  12. June 7th, 2012 at 21:26 | #12

    I recall hearing something recently about different people reacting differently to salt intake, and it having something to do with their ancestry–i.e. people from hot climates where they would have been sweating more have evolved a body chemistry that conserves salt more than people from colder climates, and, according to this line of research, hypertension caused by salt intake is mostly an issue for people from hot climates whose bodies conserve salt.

  1. May 6th, 2011 at 15:54 | #1
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