Difference between revisions of "Salt"

Latest revision as of 18:20, 21 August 2020

Salt is the most common food seasoning and food preservative used in the world. Studies and different recommendations from authorities about salt have caused people to wonder whether salt is actually healthy or not, resulting in very diverging opinions. Salt is not just simply sodium, but a mineral composed primarily of sodium and chloride. The average amount of sodium in salt is 40%.

Excessive salt intake has been linked to the worsening of multiple organs and diseases. [1] But sodium is also absolutely necessary for your body to function. This section will talk about whether salt is healthy or not, and in which amounts.

High blood pressure, arterial stiffness, stroke, cardiac arrest and kidney disease

It's scientific consensus that excessive amounts of sodium lead to high blood pressure. [2] This is understood to happen because salt provokes water retention to prevent a hypertonic environment in bodily fluids, therefore leading to a situation of higher blood flow volume which puts more stress on blood vessels. [3]

This is considerably important for people suffering from high blood pressure/hypertension.

Most current recommended intakes of sodium are below 2.3g daily for young people, and around 1.5g for people of African origins, people older than 51, and people with hypertension, diabetes and kidney disease [4] --however, the population averages around 3.4g of sodium daily. Considering that sodium makes roughly 40% of salt, you'd only have to eat 5g of salt to take 2g of sodium, which would be around a teaspoon of salt.

Most of the sodium in the average person's diet comes from processed foods, which are made very salty to appeal to the palate, as well as preserved with sodium based preservatives which may increase the sodium level without the benefit of significantly increasing the saltiness. That said, the palate can easily adjust to lower than excessive levels of salt, so by eliminating processed salted foods and replacing them with cooked-at-home foods, it'd be pretty easy to adjust the palate to be just as pleased with a safer amount of sodium intake. Salt added after cooking can also be a good practice to increase the perception of saltiness while increasing the sodium level of food significantly less.

High blood pressure and hypertension have a domino effect in the well-being of your body. Long-term high blood pressure leads to eventual damage to the heart and blood vessels, increasing the risk for kidney damage, heart attack and stroke. [5] [6] Excessive amounts of salt have also been shown to increase arterial stiffness. [7] Both the kidneys--because of the dense network of blood vessels in them--and the areas more vulnerable for strokes are very sensitive to high blood pressure.

With this information in mind, it'd then be important to understand what an 'excessive' amount of salt actually is -- and that is the matter of controversy.

For cardiovascular health, intakes of sodium higher than 5g daily were found to be worse for people with hypertension in this study. [8]

However, when looking at major studies that have been conducted recently, there's evidence that an average sodium intake (3-5g/d) could be more protective against cardiovascular disease than a low sodium intake (<3g/d), suggesting that the upper safe limit of 2.3g set in 2004 may need to be revised. [9] In this study, 17'000 people were put to the test, and a sodium intake of <3g/d was found to significantly increase the risk for cardiovascular disease. [10]

On the contrary of what recommendations say, recent studies and analyses have shown the threshold of what's considered excessive amounts of salt may be considerably higher. In this study of 133'000 people [11] [12], a higher dose than 7g/d of sodium in people with hypertension was found to increase the risk of cardiac events 1.23 times more than consuming 4-5g/d of sodium, but for people without hypertension, there was found no risk consuming 7g/d compared to 4-5g/d.

On top of that, when people with hypertension were taking <3g/d of sodium compared to 4-5g/d, the risk for cardiac events actually increased with a factor of 1.34 times higher. That means that there would be a higher risk for people with hypertension to consume not enough sodium (less than 3 grams daily, 1.34 times more risk), than the risk they'd have consuming too much sodium (more than 7 grams daily, 1.26 times more risk). These results held true even when researchers excluded people with known previous cardiovascular disease.

The study also found that people without hypertension consuming <3 g/d had higher risk, with a factor of 1.26 times higher. Considering the amount of people involved in the analysis, this is strong evidence that the amount of recommended salt intake could actually be too low in practice. It's unclear why this is because there are many confounding variables, but one possibility may be that those consuming less salt opt instead for processed sweets to satisfy tastes and sugar may ultimately be more harmful than salt.

The field is definitely polarized when it comes to optimal amounts of salt, and more clinical trials need to be conducted that exercise better controls to determine the reason for these correlations. However, current evidence suggests that at least as far as recommendations go in practice:

• decreasing amounts of salt intake in people without high blood pressure doesn't make much of a difference
• a sodium intake amount of 4-5g correlates best with good health (roughly 2 teaspoons of salt)
• 7g/d (roughly 3 teaspoons of salt) may be a safe limit for people without hypertension, and probably a little lower than 7g/d should be the limit for people with hypertension

It's also important to note that <3g/d of sodium (roughly 1 teaspoon of salt) may be too little for either group in practice. Does this still hold if a person abstains from sweets as a replacement for salt? This is unclear, but as far as the current epidemiological (correlation) evidence goes and until we have better information, there's not a very compelling reason to avoid normal amounts of sodium unless suffering from hypertension and restricting under the advisement of your doctor.

Osteoporosis

Excessive amounts of salt have been thought to cause osteoporosis. [13] Chemically it makes sense because solutes mutually reduce each other's solubility, so a high sodium diet would mean conversely lower calcium solubility. However, in practice it's not clear if this is an issue for living organisms that have complex systems of upregulating absorption, and where total calcium availability may be less important than other factors like vitamin D.

This study found that post menopausal women consuming more than 2g of sodium daily had a higher risk of osteoporosis with high sodium intake. [14] This is not exactly clear though, suggesting a 'potential' risk.

In fact, the salt correlation with bone density loss is actually not clear at all, and no association between salt intake and bone density loss/fractures has been determined. This study looks at around 70'000 post menopausal women with a follow-up of more than 11 years: [15]

"there was no significant association between calibrated sodium intake and changes in BMD at the lumbar spine, hip or total body, or incident fractures including all, other, and clinical spine sites. Higher levels of sodium intake and intakes above the WHI population median were associated with significantly fewer hip fractures."

This study has the same finding, not showing any correlation between high sodium intake and bone density loss. [16]

Research shows that there is no clear evidence supporting salt intake's correlation with osteoporosis.

"the evidence is based primarily on acute salt-loading studies, and there are insufficient data on the effects of high salt intake on net Ca retention to predict long-term effects on bone health" [17]

This issue remains controversial [18], and more clinical trials are needed. It may be that there are just too many confounding variables, but as it stands a more appropriate treatment for osteoporosis is probably supplementation under the supervision of a doctor rather than dietary sodium restriction.

Stomach cancer

There's evidence suggesting that salt may be linked to stomach cancer, however, this causality is not very clear. And it's also not entirely understood how much salt would be required to increase the chance of gastric cancer.

One factor that is proven to increase gastric cancer is the infection of H. Pylori, which causes significant inflammation and damage. H. Pylori is a bacterial pathogen, colonizing roughly half of the world's population. However, an infection of H. Pylori also tends to manifest itself with abdominal pain and burning sensations from ulcers, nausea and other symptoms.

Salt intake worsens the pathogenicity of H. Pylori, meaning that it'd make the infection have significantly worse consequences. [19]

However, as the study says, it's unclear whether salt intake by itself would increase the risk of gastric cancer, and how much salt would be required to do so.

"The overall results from cohort studies are not totally consistent, but are suggestive of a moderate direct association. Since salt intake has been correlated with Helicobacter pylori (H pylori) infection, it is possible that these two factors may synergize to promote the development of stomach cancer. Additionally, salt may also cause stomach cancer through directly damaging gastric mucus, improving temporary epithelial proliferation and the incidence of endogenous mutations, and inducing hypergastrinemia that leads to eventual parietal cell loss and progression to gastric cancer."

"Several mechanisms by which salt intake may increase stomach cancer risk have been postulated, although to date there has been no consistent conclusion."

"Ideally, dietary modification of salt intake, as well as eradication of H pylori infection, is a promising strategy for gastric cancer prevention throughout the world, especially in developing counties. However, the former strategy is more practical than the latter according to previous epidemiological studies. Future studies that address the association with salt and other dietary factors and the interactions between these factors in different aspects, e.g. molecular level, may help to shed light on the etiology of stomach cancer."

That said, while globally it may be implausible to control H. Pylori, in cases of infection in the developed world it may be preferable to directly treat the infection and address the root cause, rather than simply controlling amounts of salt to avoid aggravating the pathogen. This is particularly important given the potential cardiovascular risks of a low sodium diet in practice.

Another study suggests that there would be more factors with salt besides H. Pylori interaction that would cause cancer, albeit still unclear. [20]

"The risk of gastric carcinoma is influenced not only by H. pylori strain characteristics and host genetic determinants but also by environmental elements. One factor that has uniformly been associated with an increased risk of gastric cancer is high dietary salt intake."

"The mechanisms by which salt increases the risk of gastric cancer in humans are incompletely understood. One possibility is that salt may have direct effects on the gastric epithelium that lower the threshold for malignant transformation. Another possibility is that salt damages the gastric mucosa, thereby allowing entry of carcinogens into gastric tissue. Upregulated production of cytokines in response to a high-salt diet may also be contributory. Finally, an intriguing possibility raised by recent observations is that high salt concentrations could potentially modulate gene expression in H. pylori."

While this research may seem concerning, the science is still not clear if and how, and in what quantities, salt would actually increase the risk of gastric cancer without H. Pylori.

There are, however, ways to mitigate all of these mechanistic processes without total reduction in dietary sodium, and most of them come down to drinking plenty of water with salty food. All of the relevant damage is caused by the hypertonic concentration of salt exposed to cells (too much salt and too little water) -- be they pathogenic cells of H. Pylori bacterium of the cells lining the stomach. Mixing a salty dish with plenty of water in the stomach dilutes the salt beyond any plausible concern. It is the cases of failure to consume liquid with salty food, or even consuming only salty liquids (e.g. soupy meals without beverages as in many Asian countries where stomach cancer is prevalent) that would in theory cause the mechanistic damage from salt. Changing this pattern would at least in theory (according to the mechanisms that have been proposed) essentially eliminate the risk without necessarily lowering dietary sodium.

Potassium chloride and miso paste alternatives

Miso paste

Miso paste--fermented soy beans--is a common salt replacer in Asian countries. It has a umami flavor, and can be added to a lot of recipes without modifying the taste too much.

Miso paste also has a good amount of probiotics, as do all fermented food. However, heat kills the beneficial bacteria, with just a threshold of bacterial resistance of around 46°C--meaning that miso should be added after cooking to the food to maintain it's probiotic properties. So, cooking a traditional miso soup would mean that all the probiotics would be killed in the process, and only the beneficial effects of the soy would be left from adding miso paste.

Miso paste intake has been shown to correlate with improved health. [21] This study is based on rats, so it should be taken with a grain of salt. Contrary to what popular believes would say, there was no evidence for improved blood pressure from using miso paste instead of salt.

"Significant changes in blood pressure were not observed in the experiment."

When it comes to stomach cancer, the study also showed that miso paste actually had a reduction in risk, even though miso paste contains sodium. This is likely due to the protective effects of soy.

In this study, miso was shown to have a protective effect against stroke, despite it's salt content. [22]

"Our results suggest that miso may have protective effects against stroke despite its high salt content."

This would further suggest that sodium intake wouldn't increase high blood pressure and stroke by itself, but rather it'd be the type of foods themselves containing the salt.

Overall, miso paste is a good salt replacer, but considering that it doesn't actually make a significant difference from just using salt--if not for increased soy and probiotics intake--and that miso paste is often unavailable/expensive, it'd be more practical to just use miso paste for the recipes that need it for the taste, and use salt for the rest.

Potassium chloride

Potassium chloride is a salt of potassium (K) + chloride (Cl), instead of normal table salt being sodium (Na) + chloride (Cl). It is frequently sold as salt alternatives, usually as a 50%-50% mix of sodium and potassium salt, and is increasingly being used in processed foods as as replacement for Sodium salt to reduce the sodium content without affecting taste.

Substantial evidence suggests that it's not the total amount of sodium, but the sodium to potassium ratio that correlates to mortality.

This may be because vegetables and many healthier foods are higher in potassium, or it could be because excessive sodium and low potassium pose serious chemical challenges to equilibrium in the body where sodium and potassium processes drive nerve signals and other essential cellular functions -- cells have chemical pumps that drive sodium out and bring potassium in[23], which face greater challenges with a higher sodium to potassium ratio in bodily fluids.

Potassium Chloride has also been shown not to increase the virulence of H. Pylori, and while there's no epidemiological or experimental confirmation yet in people, this at least in theory suggests it would pose less risk, or perhaps mitigate risk, of stomach cancer.

KCl is a useful tool to decrease sodium intake, when desired, and increase potassium intake, without sacrificing the taste too much. [24]

Potassium intake is also vital for keeping blood pressure in check [25] [26], as potassium helps regulate sodium and lowers the tension in blood vessel walls.

Conclusions

Taking everything into account, it seems that the big fuss about salt is mostly unsubstantiated.

The recommendations are grossly outdated considering recent strong evidence, and would need a revision--especially when considering that the recommendations to reduce high blood pressure with low sodium intake, to then prevent heart failure, is based on weak evidence (e.g. nine studies, less than 100 people per study with a total of 479 people, and no data to show that salt restrictions reduced mortality).

It's more likely that the correlation between high sodium and increased risk of mortality would actually be because of the type of foods usually containing high amounts of salt, namely highly processed fast foods and meat, rather than the salt itself.

The most likely safe bet for salt is to keep the sodium amount between 4-5g (1.5 to 2 teaspoons of salt) daily, as more than 7g and less than 3g would increase risk of mortality. It's also important to make sure you're reaching the recommended intake of potassium and maintain a good ratio of potassium/sodium, as potassium regulates sodium and helps blood pressure directly. Considering this, it'd be more practical to adjust to a sodium intake level of about 4-5g daily and to maintain a good level of potassium intake, rather than having a low-sodium diet.

Quite a lot of people still eat too much salt in the modern world, basing their diets mainly on salt-rich fast foods. This can be easily mitigated by reducing (or preferably eliminating) fast foods--which are unhealthy for other health risks unrelated to excessive salt consumption as well--and by replacing them with home-cooked-foods.

When struggling with hypertension, the most effective things you can do to lower your blood pressure are to be careful of what you eat and to maintain a healthy weight, to avoid smoking, to avoid drinking alcohol, to exercise regularly, and to make sure you're getting enough potassium.

If you're having trouble to adjust the palate to a lower amount of salt, make use of potassium chloride to substitute some of the salt with a similar tasting compound, without increasing sodium intake, and increasing potassium intake, that some people seem to not reach recommended amounts of.