For more than 40 years, we've been told eating too much salt is killing us. Doctors say it's as bad for our health as smoking or not exercising, and government guidelines limit us to just under a teaspoon a day.

We're told not to cook with it and not to sprinkle it on our meals. The white stuff is not just addictive, goes the message - it's deadly. Too much of it causes high blood pressure, which in turn damages our hearts. We must learn to live - joylessly, flavourlessly but healthily - without it, reports the Daily Mail.

Well, I'm here to tell you that all of that is wrong. As a leading cardiovascular research scientist - based at Saint Luke's Mid-America Heart Institute, Missouri - I've contributed extensively to health policy and medical literature.

I am associate editor of the British Medical Journal's Open Heart, published in partnership with the British Cardiovascular Society, and I sit on the editorial advisory board of several other medical journals.

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In my work, I've examined data from more than 500 medical papers and studies about salt. And this is what I've learned: there was never any sound scientific evidence to support this low salt idea.

What's more, as I explain in my new book, eating too little of it can cause insulin resistance, increased fat storage and may even increase the risk of diabetes - not to mention decreasing our sex drive.

Current daily guidelines limit you to 2.4g of sodium, which translates to 6g of salt (or sodium chloride) or slightly less than a teaspoonful.

If you have high blood pressure, or belong to a group considered to be at greater risk of developing it - such as being over 60 or Afro-Caribbean - doctors even advise you to cut your intake to two-thirds of a teaspoon of salt per day.

Yet salt is an essential nutrient that our bodies depend on to live. And those limits go against all our natural instincts.

When people are allowed as much salt as they fancy, they tend to settle at about a teaspoon-and-a-half a day. This is true all over the world, across all cultures, climates and social backgrounds.

If you've been struggling to cut your intake, it may come as a relief to learn your salt cravings are normal, a biological need akin to our thirst for water.

We are essentially salty people. We cry salt, we sweat salt and the cells in our bodies are bathed in salty fluids. Without salt we'd not be able to live. And it's not only our bodies that work this way.

A yen for salt drives the elephants of Kenya to walk into the pitch-black caves of Mount Elgon to lick sodium sulphate salt crystals off the walls.

Gorillas have been known to follow elephants to eat the salt-rich droppings, while monkeys that groom one another don't do so to eat fleas, but to enjoy their salty skin secretions.

Salt is so fundamental to life that a deficiency of it acts as a natural contraceptive in all sorts of animals, including us.

A diet low in salt reduces the sex-drive, inhibits the chances of getting pregnant and affects the birth weight of infants. Clinical studies show that low-salt diets can increase the risk of erectile dysfunction, fatigue and the age at which females become fertile.

Salt helps the body withstand accidents and other traumas. Besides excessive bleeding, we experience a loss of other fluids in states of shock - for example, from burns. As the injured areas soak up fluids to speed healing, the body needs its salt reserves to keep the blood circulating and fend off vascular collapse.

So why do almost all doctors tell us that salt is bad for us?

The orthodox medical view on salt is based on a straightforward hypothesis, which says eating higher levels of salt leads to higher levels of blood pressure - end of story.

But as with so many simplistic health theories, this is based on a fundamental misunderstanding, compounded by faulty science.

The faulty hypothesis goes like this: when we eat salt, we get thirsty, so we drink more water.

The excess salt causes the body to hold on to that water to dilute the saltiness of the blood.

That water retention increases blood volume, which leads to higher blood pressure, and thus to heart disease, strokes and other serious conditions.

Although this makes sense in theory, there's a problem: the facts don't back it up.

Evidence in medical literature suggests approximately 80 per cent of people with normal blood pressure (that is, a reading of below 120 over 80) do not suffer any signs of raised blood pressure - none at all - when they increase their salt intake.

Among those with prehypertension, or higher blood pressure, three quarters are not sensitive to salt. And even among those with full-blown high blood pressure, more than half - about 55 per cent - are totally immune to salt's effects.

The dangerous myth that salt raises blood pressure began more than 100 years ago, with French scientists Ambard and Beauchard. They based their findings on studies of just six patients.

Successive researchers misinterpreted and misused their data, building on a theory that earned media attention without any solid foundation in fact.

In the early Fifties, at Brookhaven National Laboratory in New York, Dr Lewis Dahl was determined to make science fit his own preconceptions.

A man of 'strong convictions', he was a proponent of racial theories that claimed Japanese people had high levels of hypertension while Inuit tribes did not - and that this was due to the amount of salt in their diets.

He proposed to prove this with experiments on rodents.

However, as even Dr Dahl was obliged to concede, normal rats are not sensitive to salt. It does nothing to their blood pressure.

So he decided to selectively modify them through in-breeding over several generations to create what are now known as "Dahl salt-sensitive rats".

That's right: Dahl created salt-sensitive rats in a lab and then used them to prove his hypothesis that salt affected blood pressure.

Dahl popularised the notion that salt is nothing but a flavouring we add to food. He cited medical studies that, he claimed, were proof humans could survive on a quarter of the recommended levels.

But a closer look at the papers he promoted is alarming: one 1945 experiment into a low-salt diet may have killed people.

One patient placed on a restricted salt regime died soon afterwards, and another sustained circulatory collapse, due to inadequate supplies of oxygen and nutrients to the tissues - a classic symptom of salt deprivation.

One of Dahl's most dramatic experiments involved giving human baby food with high salt content to his special salt-sensitive rats. It killed them, which Dahl proclaimed as proof that baby food could be lethal for human infants, too.

Of course, human babies are much larger than rats, and the salt-sensitive rats had been genetically engineered to suffer from hypertension.

But based partly on this research, the Committee on Nutrition at the American Academy of Paediatrics concluded that infants were consuming too much sodium, and manufacturers began to lower the salt content in all kinds of food.

The link between high blood pressure and salt was established in the public mind, on the most spurious of pretexts.

But this misinformation did not take hold worldwide. The average Korean, for instance, eats over 4g of sodium a day. They feast on tteokguk, a broth-based soup full of salt, and bulgogi, grilled meat marinated in a sea of sodium-packed soy sauce. They eat kimchi - cabbage preserved in salt - with every meal.

Yet Koreans have some of the world's lowest rates for hypertension, coronary heart disease and death due to cardiovascular disease. This is known as the "Korean Paradox".

South Korea also has one of the lowest death rates from coronaries in the world, along with Japan and France.

What do people from these three countries have in common? They all eat a very high-salt diet.

Research suggests the optimal range for healthy adults is between 3g and 6g of sodium a day - about one-and-a-third to two-and-two-thirds of a teaspoon of salt. Photo / 123RF
Research suggests the optimal range for healthy adults is between 3g and 6g of sodium a day - about one-and-a-third to two-and-two-thirds of a teaspoon of salt. Photo / 123RF

The Mediterranean diet, too, widely recommended as heart-healthy, is not exactly low in salt - think of all those anchovies and sardines. Even where blood pressure does increase, the benefits of a higher salt intake - a lower heart rate, reduced insulin levels, more balanced adrenal hormones and better kidney function - are likely to outweigh any risks.

Low salt intake has several side-effects that magnify our risk of heart disease, such as increased heart rate, compromised kidney function, underactive thyroid glands, heightened insulin levels - a risk factor for diabetes - as well as heightened cholesterol.

All through lack of salt. This white crystal that has been unfairly demonised for many decades is diverting blame from the real culprit of these illnesses.

High blood pressure, cardiovascular disease and chronic kidney disease can all be caused by the real health hazard, excessive consumption of sugar.

We all need salt to live. But you could go the rest of your life, and probably extend its span, if you never ingested another gram of added sugar.

It is extraordinary that no food advertisement or leaflet in your GP's surgery ever tells you that a low-salt diet doesn't just increase your risk of an elevated heart rate, it practically guarantees it. This harmful effect occurs in nearly everyone who restricts salt intake.

The damage done by an average increase of four heartbeats a minute is compounded by other salt-related stresses inflicted on our bodies by modern life.

We lose salt by following fashionable diets such as low-carb regimes. Some medications cause salt loss. Intestinal problems including Crohn's disease, ulcerative colitis, irritable bowel syndrome and leaky gut also decrease salt absorption.

And kidney damage from refined carbs and sugar will reduce those organs' capacity to retain salt.

We may discover that low-salt guidelines have created more heart disease than they ever prevented.

They may even have been a contributing factor in the greatest public health challenge of our time: the rising epidemic of diabetes, caused in part by an increasingly common, yet little-known, phenomenon called "internal starvation".

To understand this, we need to begin by looking at the obesity epidemic.

The conventional explanation for this is an imbalance between the consumption of calories and our expenditure of energy - in other words, we eat more than we burn off.

We're told to eat less and move more, though it's obvious this strategy isn't working for everyone.

Consuming too little salt can set into motion an unfortunate cascade of changes that result in insulin resistance, an increase in sugar cravings, an out-of-control appetite and ultimately internal starvation, sometimes known as hidden cellular semi-starvation, which promotes weight gain.

Someone who appears massively overweight on the outside may be literally starving on the inside.

When you start restricting your salt intake, your body will do anything to try to hold on to it.

Unfortunately, one of its main defence mechanisms is to increase insulin levels, which it does by becoming more resistant to insulin itself. The body is then less able to shuttle glucose into cells.

That means more and more insulin is secreted to control blood glucose. This keeps the body's stored fat and protein reserves locked away. The fat cannot be converted into energy.

To make matters worse, salt restriction also stimulates hormones such as renin, angiotensin and aldosterone. They help retain the ebbing salt levels, but they also increase the absorption of fat.

So a low-salt diet doesn't just force the body to pile on fat, but prevents it from being burned off. No wonder 'Eat Less Move More' can make no difference for some.

It gets worse. If you slash salt intake dramatically, you could also develop an iodine deficiency, since salt is our best source of iodine. We need iodine for proper thyroid function, without which the metabolic rate may slow down.

A slower metabolic rate results in the body storing more fat, particularly in the organs, which in turn promotes insulin resistance. Once again, weight gain results.

Plus, low-salt diets increase the risk of overall dehydration. That's a problem because well-hydrated cells consume less energy.

Dehydrated cells leave you feeling exhausted, which encourages you to consume more calories - which are immediately translated into weight gain.

Exercise now seems unappealing. Your body cannot access its stored energy and so the brain switches into conservation mode, trying to hang on to every calorie.

Even though weight is piling on, every function in the body is behaving as though it's fighting to survive a full-scale famine.

So how much salt should you be eating? Many healthy people needn't worry about overloading. The body takes care of any excess.

Research suggests the optimal range for healthy adults is between 3g and 6g of sodium a day - about one-and-a-third to two-and-two-thirds of a teaspoon of salt.

Listen to your body. It has a built-in "salt thermostat", an interconnected set of brain sensors that monitor sodium supplies in an effort to avoid activating those starvation hormones.

And your brain would much prefer that you simply eat salt rather than having to scavenge it from vulnerable parts of the body.

So next time you feel a craving for salt, do yourself a favour and give in to it. Your body says these things for a reason.

Drop the guilt - not the salt.