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Salt is sometimes known as "white death" due to the belief that an excess intake of salt can cause substantial damage to health.

What evidence exists to support or contradict the idea that excess salt intake can cause substantial health damage? Is it better to avoid salt altogether?

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    and no, just because some dose is lethal doesn't mean you should not consume/ingest something at all. Oxygen is lethal, so is water. Yet without it you'd die quickly. The human body needs cyanide, yet more than a few micrograms will kill you. And it's the same with salt as well. That said, an average human being gets enough salt for his daily dietary requirements through his normal food intake (especially processed foods, breads, etc.) and doesn't need to add salt to his diet explicitly by salting his food extra.
    – jwenting
    Commented Mar 8, 2011 at 8:04
  • jwenting: "the human body needs cyanide" - any source on that? I'd be very surprised if it is the case.
    – johanvdw
    Commented Sep 26, 2011 at 11:03
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    Scientific American has an interesting article - scientificamerican.com/…
    – DanBeale
    Commented Sep 26, 2011 at 15:37
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    the biggest problem these days, is that there where so many health rules and ideas put into place in the 50s-80s things like butter will kill you, eat margarine, that have slowly been drilled into people, that when the release articles like butter is better then margarine, (in moderation of course) it throws everyone off. all of sudden some fats are good, some are bad, and its the inverse of the last 30 years, dietairy guidelines are the biggest ever revolving science around.
    – Himarm
    Commented Jan 23, 2015 at 19:57
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    As with most controversial health questions, I believe this is too complex to adequately address here. A number of nutritionists and doctors claim that salt (or certain forms of more "natural" salt) don't cause problems with blood pressure as previously thought. They may or may not be right, but by the standards of our site, we can easily "prove" there are studies that show a causal correlation. We may also be able to "prove" no correlation. This is because there is (apparently) evidence on both sides. So I doubt an answer will be found which can satisfy a true skeptic on this type of issue.
    – Flimzy
    Commented Jan 27, 2015 at 3:45

5 Answers 5

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Toxicity of a substance must be investigated in different ways:

  1. Acute toxicity

    This corresponds to taking a large dose all at once. In the case of sodium chloride, toxic effects are encountered at 500-1000 mg/kg body weight. The effects include vomiting, ulceration of the gastrointestinal tract, muscle weakness and renal damage, leading to dehydration, metabolic acidosis and severe peripheral and central neural effects.
    The estimated fatal dose of sodium chloride is approximately 750 to 3000 mg/kg.
    Also see (1, 2) for many more sources.

  2. Chronic toxicity

    This includes non-carcinogenic effects on health. There seems to be a link between salt intake and some hypertrophy of the heart - which is a risk factor for heart disease. The generally known medical advice to use less salt is actually due to a different factor: reducing salt reduces blood pressure in hypertonic subjects. In other words, if you have high pressure, then reducing salt is beneficial. The effect of reducing salt in individuals with normal pressure instead is disputed.

    Reduction of dietary sodium is generally recommended as a nonpharmacological treatment for patients with essential hypertension. In normotensive adults a significant reduction in sodium intake is needed to achieve a modest reduction in blood pressure.

  3. Carcinogenic effects

    Salt has no known carcinogenic effects and no carcinogenic effects are expected to be found (1, 2).

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    Further data regarding salt toxicity
    – Casebash
    Commented Mar 8, 2011 at 12:04
  • there might also be potentially non-toxic yet health-detrimental effects from Sodium/Potassium imbalance (it's been a long while since I read on the topic so don't remember any details)
    – user5341
    Commented Jun 21, 2011 at 17:22
  • The conclusion of this 2011 study was that people with the lowest levels of sodium intake at the start of the study had a 56 percent higher risk of dying from cardiovascular disease than people with the highest levels. Moreover, among those participants who had normal blood pressure at the start of the study, urinary sodium appeared to have no effect on the development of high blood pressure over six and a half years.
    – elbatrofmoc
    Commented Sep 19, 2012 at 9:10
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In addition to the other answers:

Does this mean that it is best not to use any salt at all?

Certainly not. Salt is necessary. If you don't eat enough salt you may end up with hyponatremia.

From wikipedia:

Hyponatremia is the most common electrolyte disorder. Its frequency is higher in females, the elderly, and in patients who are hospitalized. The incidence of hyponatremia depends largely on the patient population. A hospital incidence of 15–20% is common, while only 3–5% of patients who are hospitalized have a serum sodium level of less than 130 mEq/L. Hyponatremia has been reported in up to 30% of elderly patients in nursing homes and is also present in approximately 30% of depressed patients on selective serotonin reuptake inhibitors.[2]

Apart from them it is a condition which is quite common in people who are running a marathon and loose a lot of salt through sweating, while drinking too much water See eg: http://www.nejm.org/doi/full/10.1056/nejmoa043901

This is also true for less intensive sports:

Sodium depletion is a recurrent theme in heat cramping, and is reported to be one of the factors contributing to cause, treatment, and prevention of exercise-associated muscle cramps . Stone, M.B., J.E. Edwards, C.L. Stemmans, C.D. Ingersoll, R.M. Palmieri, and B.A. Krause. Certified athletic trainersʼ perceptions of exercise-associated muscle cramps. J. Sports Rehab. 12:333-342, 2003. cited in http://www.csun.edu/~lisagor/2009%20Fall/608-09Fall/608-1.Sweat%20and%20Sodium%20Losses%20in%20NCAA%20Football%20Players.pdf

In that paper you will also notice that some people lose a lot of salt through sweating, and for those people salt intake has to be higher.

Finally since this site is about skepticism: some groups are clearly vulnerable to hyponatremia. For those people it is perhaps a bad advice to limit salt intake. The major reason why salt is seen as 'bad' is the fact that it causes high blood pressure. But it only influences high blood pressure in a relatively small group of people. See eg:

Dietary sodium restriction for older hypertensive individuals might be considered, but the evidence in the normotensive population does not support current recommendations for universal dietary sodium restriction. "

http://jama.ama-assn.org/cgi/content/abstract/275/20/1590

One segment of the public health community—funded by the the Na- tional Heart Lung and Blood Institute and endorsed by many journals in the field—has decided that salt is a public health menace. Therefore, salt consumption must be drastically curtailed. The force with which this conclusion is presented to the public is not in any reasonable balance with the strength of the evidence.

http://www.stat.berkeley.edu/~census/573.pdf

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  • whoever downvoted: please explain why. There is a reference, and I think this answer (although short) is a useful addition to the other answers because it focuses on a part of the question that was not covered in the other answers.
    – johanvdw
    Commented Sep 26, 2011 at 12:41
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    Since salt is actually contained in almost all that we eat, not adding any salt would not necessarily lead to hyponatraemia... your reference supports that salt is necessary, not that not using salt at all is a bad thing (which is your main claim).
    – Sklivvz
    Commented Sep 26, 2011 at 13:08
  • Sklivvz: the question is literaly: "Does this mean that it is best not to use any salt at all?". That would exclude things that you eat that contain salt. I've expanded my answer, because I do think we should be more skeptical on the salt recommendations. I know for sure that I have to take care that I eat enough salt. But I'm not eating a lot of processed food that contains sugar and saturated fats (that lead to high blood pressure), and I do exercise a lot (which leads to a lower blood pressure).
    – johanvdw
    Commented Sep 26, 2011 at 14:07
  • When I exercise, especially long distance running, I need to east a small handful of salt afterwards otherwise I get painful cramps, as I get very little salt in my diet- avoiding processed foods reduces your salt intake dramatically
    – Rory Alsop
    Commented Sep 26, 2011 at 16:59
  • @Sklivvz: the British salt tax in India, which prevented poor people from using very much salt at all, is believed to have led over a million deaths. Many of these were due to heat exhaustion. So it's not enough just to eat plain rice and vegetables; you really do need added salt. Of course today, salt is added to so many products that you probably don't need any additional salt over the amount that manufacturers have added. But this depends on exactly what you eat.
    – Peter Shor
    Commented Nov 5, 2017 at 18:29
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Signs don't look so good. See this article http://www.cspinet.org/nah/articles/salt.html, which refers to a number of recent (and not so recent) studies. (There are references to the actual studies in the PDF version; oddly in the html article the superscript numbers are there but the notes are missing.) Some highlights:

  • A 2009 meta-analysis of 13 studies found that cutting salt reduces blood pressure and also lowers risk of heart attacks and strokes
  • long-term exposure to excess sodium means eventual high blood pressure for 90% of Americans
  • even moderately-elevated blood pressure is associated with increased risk
  • there's some suggestion that elevated blood pressure may be associated with dementia
  • there's suggestion that salt is harmful to the cardiovascular system directly, regardless of pressure

Note that many of the studies are newer than the 2003 paper referenced in Sklivvz's answer.

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Yes, The relationship between sodium intake and hypertension is extremely well studied.

Does sodium intake affect hypertension?
Double-blind study of three sodium intakes and long-term effects of sodium restriction in essential hypertension.
http://www.ncbi.nlm.nih.gov/pubmed/2573761

Abstract
20 patients with mild hypertension (average supine blood pressure without treatment, 164/101 mm Hg) reduced their salt intake to 50 mmol (3 g) per day for a month. They then entered a 3 month double-blind randomised crossover study of three levels of sodium intake: 200, 100, and 50 mmol per day. Blood pressure was significantly reduced on the middle and lowest sodium intakes. The average fall in blood pressure from the highest to the lowest sodium intake was 16/9 mm Hg. Patients continued to restrict their sodium intake for a further year. In 16 of the 20 patients blood pressure remained well controlled with salt restriction alone. Supine blood pressure at 1 year was 142/87 (SE 3/2) mm Hg with a 24 h urinary sodium excretion of 54 (7) mmol. These results show a progressive blood pressure fall as salt intake is reduced and that, in many patients with mild essential hypertension, blood pressure can be controlled without the need for drug therapy.

More recent examples confirming the correlation:
(these are the first four results I got on scholar.google.com key words: [sodium intake hypertension] 2011 or more recent. The fifth result was specific to Chinese adults so I stopped there.)

(2012)

Over time, higher sodium intake is associated with increases in SUA and UAE. Among individuals with higher SUA and urine UAE, a higher sodium intake is an independent risk factor for developing hypertension.

(2014)(correspondence, specifically deals with some of the recent "confusion" that the question refers to. I don't feel that I am qualified enough to interpret any further but I recommend looking at it.)

After the IOM report was released, the TOHP data showed a direct, progressive relationship between lower sodium intake (down to intake below 1500 mg per day) and lower cardiovascular risk and there was no indication of a J-shaped curve

(2012)

Sodium intake is positively associated with SBP and risk for pre-HBP/HPB among US children and adolescents, and this association may be stronger among those who are overweight/obese.

(2013) (Meta-Analysis)

High quality evidence in non-acutely ill adults shows that reduced sodium intake reduces blood pressure and has no adverse effect on blood lipids, catecholamine levels, or renal function, and moderate quality evidence in children shows that a reduction in sodium intake reduces blood pressure. Lower sodium intake is also associated with a reduced risk of stroke and fatal coronary heart disease in adults. The totality of evidence suggests that most people will likely benefit from reducing sodium intake.

So, is this just for hypertensive individuals or everyone?
In another study "Effects on blood pressure of reduced dietary sodium and the Dietary Approaches to Stop Hypertension (DASH) diet"
http://www.nejm.org/doi/pdf/10.1056/NEJM200101043440101

participants ate foods with high, intermediate, and low levels of sodium for 30 consecutive days each, in random order. ... The effects of sodium were observed in participants with and in those without hypertension, blacks and those of other races, and women and men. ... As compared with the control diet with a high sodium level, the DASH diet with a low sodium level led to a mean systolic blood pressure that was 7.1 mm Hg lower in participants without hypertension, and 11.5 mm Hg lower in participants with hypertension.

Finally, what's the association of heart disease with blood pressure? Blood pressure, stroke, and coronary heart disease. Part 1, Prolonged differences in blood pressure: prospective observational studies corrected for the regression dilution bias. http://www.ncbi.nlm.nih.gov/pubmed/1969518

Within the range of DBP studied (about 70-110 mm Hg), there was no evidence of any "threshold" below which lower levels of DBP were not associated with lower risks of stroke and of CHD. ... prolonged differences in usual DBP of 5,7.5, and 10 mm Hg were respectively associated with at least 34%, 46%, and 56% less stroke and at least 21%. 29%, and 37% less CHD. ... The DBP results suggest that for the large majority of individuals, whether conventionally "hypertensive" or "normotensive", a lower blood pressure should eventually confer a lower risk of vascular disease.

This study was particularly focused on diastolic, so here are a couple that are concerned with systolic as well. http://circ.ahajournals.org/content/100/4/354.short
http://hyper.ahajournals.org/content/13/5_Suppl/I2.short

In conclusion, hypertensive and normotensive (all) people who cut back on their sodium(salt) intake should experience a lower (and thereby safer) blood pressure.

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  • I'm still learning this site, if there isn't enough information or anything I can change to improve this answer, please let me know.
    – Adam Phelps
    Commented Jan 23, 2015 at 1:54
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    @bharal: You are comparing the wrong numbers. The risk of 142/87 vs. normal is irrelevant. The absolute risk level of 164/101 vs 142/87 is the relevant number to compare with the lifestyle cost of a drastic diet.
    – Oddthinking ♦
    Commented Jan 23, 2015 at 2:51
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    @Adam: My ignorant understanding is that, in patients with hypertension, sodium intake is important. In healthy patients, sodium intake is relatively unimportant. Your answer only looks at hypertensive patients, so it may still be the case that salt is being wrongly blamed for making healthy people unhealthy.
    – Oddthinking ♦
    Commented Jan 23, 2015 at 3:00
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    @bharal: Imagine this scenario: The doctor says "Without surgery, you have 10% chance of surviving 5 years. With surgery, you have a 70% chance of surviving 5 years." Your friend says "Only 70% chance? After drastic surgery? That's really low. No point." In that case, you would hopefully ignore your friend. It is low, but it is much higher than 10%. That seems to be the same situation being described here.
    – Oddthinking ♦
    Commented Jan 23, 2015 at 3:04
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    @Oddthinking Thanks for pointing this out, I hope I have improved my answer. I actually thought the same as you did, that for healthy individuals a little more or less salt wouldn't matter. This doesn't actually seem to be the case.
    – Adam Phelps
    Commented Jan 23, 2015 at 5:42
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It is possible to consume a lethal dose of salt, especially for small children. There has been at least one case where an adult died of a salt overdose. In this case 45-60 grams were consumed, but the lethal dose is estimated to be lower. The lethal dose is also far smaller for children.

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    It is also possible to die of a water or oxygen overdose :)
    – the JinX
    Commented Mar 10, 2011 at 14:44

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