Cut Back on Salt?

Low-salt salt!

Medical lore, for at least half a century, has decreed that a reduced-salt diet is heart-healthy. This piece of medical mythology seems about to be reversed, as was the fate of dietary cholesterol. A recent article in the prestigious medical journal Lancet seems to show that the medical profession has got this reduced salt business exactly backwards.

For most people, there is no need to reduce salt (sodium) intake. In fact, substantial reduction of salt intake can be very harmful, more harmful than excessive salt intake. This will be presently explained. Dr. Mike’s dietary rule on salt for the last 25 years has been, “Don’t worry about it, just don’t gorge on the stuff.” Why such a blasé attitude? Dr. Mike looks at physiology, medical research, and medical lore (that which is taught in all the medical schools). The first two get most of the weight, and that was the conclusion he reached.

The physiology

How does the body manage salt? “Very tightly” is the short answer. Here is mine for the last 20 years. No matter what I was or wasn’t doing, that sodium level never changed very much.

The sodium is regulated quite tightly, to within ±2%. This is “lock” for the human body. Many of our blood test numbers are all over the place, but not this one. So how does the body do this? We don’t have organs that store salt. We do have this ability for some other minerals, but not salt.

Our available salt is that which is circulating in our blood stream. What happens is fairly simple. The salt gets into the blood via the food we eat and drink. We can’t synthesize it. If there is too much, the kidney can selectively dump salt to maintain the proper proportion. If too little salt, the kidney can dump water. This is how kidneys works. They regulate and clean by selectively dumping stuff. More on how the kidneys work here. This regulation system has its limits, and the kidneys will not be able to do their job if there is way too much salt, or way too little.

The Medical Research

How much salt is too much? How much is too little?

Here is where it gets interesting. Per the medical lore, one would readily believe that the lower the better. The American average salt consumption is 3400 mg/day. The standard recommendation is < 2300 mg/day. (This is a painfully bland diet.) But isn’t there a danger? We can’t make salt. If we don’t get enough, it might get too low, which is quite dangerous. However, with the average being 3400, maybe low salt is not very common. We will be coming back to these numbers, so bear them in mind.

There are never any warnings given for too much sodium reduction. We suppose the doctors are trying to second guess their patients and compensate for any likely misbehavior. The doctoral presumption is that the patient won’t cut salt very much, and certainly not to the 2300 mg per day guideline.

So where did the low salt=heart healthy come from?

As research goes, there are papers dating back to the 40s that indicates excess salt raises the blood pressure—slightly. (Like 3 mmHg out of 120, a very small amount.) Why might this be? Well, if you eat a lot of salt you will get thirsty and drink a lot of water. Where does that water end up? In the bloodstream diluting all that salt. More stuff in the bloodstream, more blood pressure. Of course, it is way more complicated than that, and, amazingly, here in 2018, blood pressure regulation remains quite poorly understood.

Lets get back to cutting salt. Is a 3 mmHg decrease in blood pressure worth it? Why not. High blood pressure is a risk factor, so why not go after it? However, that’s not the right question. What we really want to know is: does the increase in blood pressure due to excess sodium cause more heart attacks? Well, a recent research paper (free version found here) in the Lancet, the top British medical journal, found some very very unexpected results:

First of all, they did find that indeed, more salt raises blood pressure, per standard lore. So far so good, But what about cardiac events (heart attacks and strokes)?

The study divided the various people, some 100,000, into three groups based on salt consumption. Consumption was higher than one would expect in all three groups. We love salt, it seems.

The top group, predominantly Chinese communities, consumed an average of 5750 mg of salt per day, far higher that Americans and well over double the recommended intake. This group showed a non-significant increase in cardiac event (heart attacks), and a strong association with strokes. (Strong: in a given year, one additional person out of 2500 will get a stroke. This is about a 10% increase.)

For the middle group, consuming on average 4700 mg per day, no increase in cardiac events was seen. This seems puzzling, does it not? 4700 mg per day is twice the WHO recommendation! But that’s what they found.

Well, OK, fine. Maybe the low salt cohort was better off still. And this is the most amazing part of the finding. The lowest third, still consuming an average of 4000 mg per day, saw an significant increase in cardiac events. How much? Around one more per thousand per year. Currently about 2.5 people per thousand will have a heart attack in a year, so this is a 40% increase! What are we saying here: specifically, a low salt diet is associated with a 40% increase in cardiac events. As they sheepishly put it: The association between mean sodium intake and major cardiovascular events showed significant deviations from linearity (p=0·043) due to a significant inverse association in the lowest tertile of sodium intake (lowest tertile <4·43 g/day, mean intake 4·04 g/day, range 3·42–4·43; change –1·00 events per 1000 years.”

Who ordered this? it seems, up to a fairly high point, more salt is good for you. Because salt caused a slight increase in blood pressure, it was demonized, and if this report is credible, it was demonized to our detriment. And for fifty years has been simply taken on faith, and no one bothered to see if that tiny blood pressure increase actually meant more heart problems.

Is the report credible?

The report seems credible. They weren’t looking for the result they got, and (go read the abstract) they down play it.

It is an epidemiological study. These are subject to mischief, but mainly so if the researchers are looking for confirmation. Why this? An epidemiological study involves a lot of statistical manipulation, data selection, and so on. Ethical researchers will unconsciously put a finger on the scale. They will remember data that was supportive, lose data that wasn’t, all without malice. Been there, done that. So when researchers report something contrary to what they expected, it’s usually worthwhile paying attention.

So, enjoy your salt. At a level less than the Chinese, but not much.

  1 comment for “Cut Back on Salt?

  1. Jim
    September 24, 2018 at 1:17 pm

    Hey docs,

    What’s your opinion of the salt substitutes that have potassium added?

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