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Dr. Peter Brukner OAM3 min read

Show me the evidence: The salt myth

The belief that sodium, which makes up 40% of table salt, is bad for our health is not supported by research.

Many people still beleive that too much salt is bad for us, but in fact, we have evidence that consuming too little is likely much more harmful to our health than consuming too much.

Salt and lifespan

Hong Kong females consume more than 8 grams of salt per day and have the longest life expectancy in the world. Low sodium diets are also associated with increased risk of dying. One study of more than 100,000 people found that a daily intake of sodium equivalent to 1-2 teaspoons of salt was associated with the longest lifespans. Sodium intakes lower than this level were actually associated with an increased chance of dying.

Fortunately, the Australian dietary guidelines now recognize that previous recommendations to limit sodium intake were not evidence based, and a restricted intake is now no longer recommended for individuals.

Why was salt restricted in the first place?

The myth that sodium is bad for us likely arose from a basic understanding of blood pressure. Sodium is necessary to hold fluid within our blood vessels, acting to increase our blood pressure. The effect of restricting our salt intake on blood pressure however, is actually quite small. One meta-analysis found that sodium restriction, led to a less than one point fall in blood pressure on average after 6 months. It is therefore questionable as to whether sodium restriction can lead to any meaningful reduction to blood pressure in the real world.

In fact, high blood pressure has been shown to be more related to high insulin levels caused by insulin resistance than it has to do with sodium intake. Healthy kidneys are usually able to excrete large amounts of sodium if needed without consequence. When insulin is high however, as it is in insulin resistance, the handling of sodium by the kidneys is dysregulated, causing much more retention of sodium within the body.

Eating sugar and vegetable oil, both common in processed foods can cause this insulin resistance. Processed foods also tend to be low in potassium, which is needed for the kidneys to excrete excess sodium. And so the combination of high sugar and vegetable oil levels, and low potassium levels, in processed foods drive sodium retention within the body, and ultimately contribute to high blood pressure.

Why salt is so important

One underappreciated role of sodium is the health of both our muscles and bones. Diets deficient in sodium have been implicated in increased risk of osteoporosis and fracture, with experimental studies proving that sodium is an essential part of both bone and muscle.

Interestingly, diets deficient in sodium can lead to an increase in fat rather the building of bone and muscle. It’s also worth mentioning that other electrolytes, including magnesium and potassium, are also important in bone and muscle health, and should be considered essential nutrients. Potassium can often be obtained from ‘salt alternatives’, and with the permission of your doctor, you may consider supplementing with magnesium.

Sodium also appears to be important for the functioning of the immune system. It is very likely that sodium, along with other electrolytes, has an anti-microbial role in our bodily secretions and could be an important line of defence against infections.

In summary

Salt plays an important role in regulating many bodily functions. In fact, not getting enough salt can be extremely detrimental to our health. Given that any excess salt in our diet is naturally (and safely) excreted by our body, the old advice of restricting sodium should be taken with a (very) large pinch of salt.

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