Comment by glastra | Hacker News Reader

Comment by glastra | Hacker News Reader

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Certainly. The first sentence already instilled a sense of "they're full of it" in me. I know that's biased.

I checked one of the papers they refer to [0] and... well, they fed mice (not humans) a diet with an 8- to 16-fold increase in salt.

As with all nutrients, there is an optimal intake range, and anything below or above that is by definition sub-optimal. In humans, the optimum for sodium intake per day seems to be well above dietary recommendations, but also well below 16 times the amounts described in those recommendations.

Also, it is worth noting that the first sentence in the linked paper is again repeating the same unreasoned "we all know salt is bad" dogma. Diets high in salt in the western world are also high in many, many other things that are bad for you. Epidemiology is useless to derive new information, it only works to establish future work or to deny previous hypotheses.

[0]: http://sci-hub.tw/https://www.nature.com/articles/s41593-017...

Across populations the average salt intake is around 3.7 grams of sodium per day.

Sodium intake is actually regulated by the body, just like protein. Your body demands more salt when it needs it. Which means that around 3.7 grams might actually be the optimal amount of sodium intake.

There are many studies showing that the standard recommendation for reducing the salt intake is bullshit. Not only that, but reduced salt intake is linked to obesity and sugar cravings.

Also before refrigerators, like in the 19th century, people consumed a lot more sodium because salt was the primary way to preserve food, especially meat. All modern chronic diseases were rare back then ... and yes, heart disease was harder to diagnose, but improvements in technology can't explain it fully, plus we are also talking of diabetes and cancer.

For skeptics, I recommend reading "The Salt Fix" which provides a good overview of the history and of various studies: http://thesaltfix.com/

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I'm not saying that healthcare professionals are idiots.

The problem is that healthcare is reductionist. Studies that properly use the scientific method don't lie, but the problem is that people often reach the wrong conclusions.

It's like in that fable in which a group of blind people are told to feel and describe an elephant, only in real life some of the blind people have more political clout than others.

I have been wondering about this. Does anybody know what the original "salt leads to hypertension" paper was?

Maybe someone thought about it mechanistically in the sense that more sodium in our blood also means more water (to keep both electrolyte balance and dilution in acceptable ranges to sustain life). More water means more blood volume or pressure if volume is limited.

Someone then probably tried to prove this by checking whether dietary salt intake leads to hypertension. However, medical and nutritional science are very limited in the ways they can conduct research. So they probably did an epidemiological study and saw that populations with hypertension also had a high dietary salt intake. Proof! Except... well, no.

Our kidneys are perfectly capable of balancing this out as long as we don't ask too much of them. More salt in your food than you need? More sodium in your pee. Less salt in your food than you need? Well, you're screwed.

Edit: Sorry for being unable to provide a direct answer to your question, but I felt compelled to reply.

Edit 2: After a search in Google Scholar, the earliest study I could find is from 1950 [0]. They studied the link between salt and hypertension in rats by replacing their drinking water with 2% salt solutions and measuring their blood pressure. It seems to me that all non-epidemiological studies are useless extremes... With no "clean" water (all water intake was hypertonic) the kidneys can't really dispose of much.

[0]: http://sci-hub.tw/https://journals.sagepub.com/doi/abs/10.31...

Edit 3: The actual paper recognises in the discussion (with citations) that it is impossible to cause hypertension in rats without artificially controlling all their water intake. Wow. Even if all water is salted, as long as it's iso- or hypotonic there is no hypertension.

I read long ago that a famous american cardiologist simply asserted that high salt intake leads to high blood pressure, and that it has been known as a fact since then.

Regrettably I can't find the source.

There have been studies showing that, but they've been inconclusive according to the meta reviews.

It's like with cholesterol, i.e. the claim that eating saturated fat can increase LDL particles in your bloodstream (it can), but to jump from there to claiming that increased LDL causes heart disease is a stretch, because LDL is just a transport mechanism and naturally, it depends on what it transports.

People are inclined to search for easy solutions. But unfortunately nothing is easy about our metabolism.

There have also been studies showing no meaningful long term association between salt intake and high blood pressure as well.

The stories that get retold, aren't the ones that are true, but often the ones that are simplest to tell.

Just an anecdote, from my experience of water-only intermittent fasting for 5 days. First time I did it, from around day 3, I will start feeling dizzy, if I suddenly standup from either lying down or sitting in a relaxed posture. Later I read that it was caused because of low blood pressure due to no salt intake. The next time I did intermittent fasting, I took some salt with my water, and the dizziness problem was not there.

>I checked one of the papers they refer to [0] and... well, they fed mice (not humans) a diet with an 8- to 16-fold increase in salt. As with all nutrients, there is an optimal intake range, and anything below or above that is by definition sub-optimal. In humans, the optimum for sodium intake per day seems to be well above dietary recommendations, but also well below 16 times the amounts described in those recommendations.

Is there some underlying assumption that those researches are idiots and didn't know all that?

The logical interpretation is that they gave 8- to 16-fold increase in salt purposefully, because they cared to see whether there are any specific effects mediated through salt. In over words, they want to put the effects on full blast to magnify responses and be able to see some novel connection, not to see how a mouse cops with mild over-consumption of salt.

Specifically, the article says that they found it resulted "in increased vulnerability of the brain to autoimmunity", which one wouldn't expect from sub-optimal salt intake alone. This is not some rehash of "very high salt = blood pressure, duh!".

Oh, not at all. They are not idiots. That paper was written with a purpose which was properly met (mainly getting to publish and, to a lesser extent, to confirm a previous notion or bias).

The issue is reporting of results to the public. Someone feeds mice a ridiculous amount of salt and notices they have some health issues. Let's assume for an instant that this is somehow useful for some reason (I mean, salt poisoining has been known for millenia and people actually commit suicide by drinking saturated salt solutions). Even in that case, journalists are still distilling the whole thing into "more salt is bad", which is what the average person will understand. The general public doesn't read scientific literature with a critical thinking mindset, if at all.

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