The truth about low salt and high blood pressure

For decades, we’ve been told to reduce the amount of salt in our diet. As every medical student is taught, salt raises blood pressure, and high blood pressure (hypertension) causes heart disease, stroke and heart attacks.

Salt – or table salt (sodium chloride) – is the main source of sodium in our diet, and it’s needed to regulate fluids in our body. Too much salt and we start retaining fluid, which increases the pressure exerted by blood on blood-vessel walls – and that’s hypertension, or so the theory has it.

Ideally, we should be consuming no more than 6 g, or a teaspoon, of salt per day. The World Health Organization says it should be 5 g/day and health agencies in Finland want to see that brought down further to just 3 g/day, while a measly 2.3 g/day has been proposed by Canadian authorities. Most of us are averaging around 8 g a day, with much of that coming from the salt that’s added to processed foods.

If we could all reduce our intake to recommended levels, there would be 14 percent fewer deaths from stroke and 9 percent fewer deaths from coronary heart disease in hypertensives, say researchers, and reductions of 6 percent and 4 percent, respectively, in people with normal blood pressure levels. Worldwide, that would translate to 2.6 million fewer deaths from heart disease every year.1

The lobby group World Action on Salt and Health (WASH) believes that the amount of salt we consume is the single biggest factor in controlling blood pressure, more important than either exercise or changing to a diet of fruit and vegetables.

The UK’s Public Health England is equally as categorical. In its latest report on the salt in our diets, it states that “there is an established relationship between salt intake and risk of high blood pressure [and] high blood pressure is a risk factor for cardiovascular disease.”

Low salt, high deaths

But over the past 20 years, researchers have come up with findings that contradict the theory. The latest come from researchers at McMaster University, in Canada, who looked at the health and diets of 133,118 adults (median age 55 years), 63,559 of whom had high blood pressure while the rest had normal readings. They discovered that those with the lowest levels of urinary sodium excretion – less than 3 g/day – suffered more fatal and non-fatal heart attacks and strokes than those excreting larger amounts.2

The pattern was the same whether individuals already had high blood pressure or not, although the researchers suggested that the low-salt guidance may be most relevant to hypertensive patients who are habitually consuming large amounts of salt.

Yet driving down the levels of salt we consume could be causing unexpected health problems, say the researchers. As lead researcher Andrew Mente said: “Low sodium intake reduces blood pressure modestly, compared to average intake, but low sodium intake also has other effects, including adverse elevations of certain hormones which may outweigh any benefits. The key question is not whether blood pressure is lower with very low salt intake; instead, it is whether it improves health.”

This supposed anomaly was observed years earlier with the first US National Health and Nutrition Examination Survey (NHANES) in 1984. At the time, researchers noticed that people who had too-low levels of minerals, especially calcium, potassium and magnesium – which are found in salt – were far more likely to suffer hypertension.

Puzzled by this, researchers from the University of California at Davis took a look at more recent NHANES data – from 10,033 participants in NHANES III and 2,311 in NHANES IV – and found the exact same thing. Those with low levels of minerals in their diet had higher blood pressure, especially high systolic pressure (the first number in a blood pressure reading, taken when blood is being pumped).3

Other researchers over the years have also uncovered this same phenomenon. A team from the Albert Einstein College of Medicine in New York, who monitored the health of nearly 3,000 people with mild or moderate hypertension, found that those with the lowest levels of sodium – and mainly men – were more than four times more likely to suffer a heart attack than those with the highest levels.4

More harm than good

Researchers from the University of Leuven in Belgium have gone further: they question the health guidelines for lowering salt intake and argue that it causes more harm than good. They tracked the health of more than 3,600 adults for nearly eight years; at the start, none had heart disease, and more than 2,000 had normal blood pressure. During the trial, 50 participants with low levels of urinary sodium died, compared with 24 in the medium-sodium group and 10 in the high-sodium group (death rates of 4 percent, 2 percent and 0.8 percent, respectively).

Indeed, the rate of heart-disease deaths was considerably higher in those with the lowest sodium levels – and there was no link between high levels of sodium from salt and high blood pressure.

“Our findings refute the estimates of computer models of lives saved and healthcare costs reduced with lower salt intake,” said lead researcher Katarzyna Stolarz-Skrzypek.5

As the Belgian researchers make clear, the estimate of lives saved by reducing salt intake is just that – an estimate, not hard fact. There are several biological reasons why eating very low levels of salt may have counterproductive effects and perhaps be dangerous to our health:

1) When we eat too little salt – which is packed with minerals essential for the healthy functioning of our bones, muscles and immune system – the body releases renin, an enzyme, and aldosterone, a hormone, which increase blood pressure. This would explain the supposed anomaly of high blood pressure in those consuming the lowest amounts of salt.

2) The kidneys moderate the release of sodium according to the amount being ingested, so there is no straight-line correlation between the salt you consume and the amount of sodium in your body. Such regulation explains the individualized responses to lower salt intake, with some seeing their blood pressure skyrocket while others
drop dramatically.

3) Eating less salt increases insulin resistance, a precursor of type 2 diabetes and heart disease. A study of nearly 400 hypertensives discovered that those who had restricted their salt intakes had higher levels of blood glucose and insulin – released by the pancreas to break down sugars in foods – than those eating high levels of salt.6

Some researchers from the Albert Einstein College of Medicine believe the truth will be known for sure only when there’s been a major controlled clinical trial to see how people on a low-salt diet fare over many years. But that will be too expensive to carry out. Instead, says Hillel Cohen, one of the researchers, all we’re left with are promises of health benefits supported by “shaky science” and “wild extrapolations.”7

Can salt save lives?

Lowering salt intake may do more harm than good, according to researchers from the University of Leuven in Belgium, who tracked the health of more than 3,600 adults for nearly eight years.

During the trial, 50 participants with low levels of urinary sodium died, compared with 24 deaths in the medium-sodium group and 10 in the high-sodium group (death rates of 4 percent, 2 percent and 0.8 percent, respectively).

Not refined

It’s not about the amount of salt – it’s the type of salt that matters, argues Dr David Brownstein, author of Salt Your Way to Health (Medical Alternative Press, 2006) and director of the Ce
nter for Holistic Medicine in Michigan.

Most of us consume refined salt, which is stripped of most of its health-giving minerals. Food-grade salt contains mostly sodium and chloride, and a little iodine to prevent goiter (a swollen neck due to an enlarged thyroid gland).

By comparison, unrefined salt contains around 80 trace minerals, which help to balance adrenal gland function, enable the body to naturally detox, raise pH levels (making our body more alkaline than acid), improve lipids, lower blood pressure, lower insulin levels, and help prevent muscle aches and cramps, says Brownstein.

So, what is unrefined salt? It’s not the sea salt we see in stores, says Brownstein. Many refined salts carry that label, but it’s misleading as all salt came from the sea at some point.

Unrefined salt contains all its 80 or so minerals, which should be listed on the product label. The minerals also give the salt a slightly different color from the pure white of refined salt. Some may be grayish and others red, depending on mineral levels. Unrefined salt is not fine, and you shouldn’t be able to sprinkle it on your food from a standard salt shaker.

He recommends two products: Celtic Sea Salt (available from the Grain & Salt Society, www.celticseasalt.com) and Redmond’s Real Salt sea salt (www.realsalt.com).

Pass the salt: A theory is born

The idea that salt is related to blood pressure was first put forward in 1904 – and refuted just three years later. The findings then flip-flopped over the next 40 years until Duke University researcher Wallace Kempner treated some hypertensive patients with a low-salt diet.

But it was Lewis Dahl, a physician at Brookhaven National Laboratory in New York, who put the salt theory center-stage. He carried out research in various populations and noted that hypertension was commonly seen with higher levels of salt intake, while the problem was rare in populations that consumed very little salt.

As it was only an observation, Dahl tested his theory in countless experiments with rats. Over the years, he was able to breed salt-sensitive and salt-resistant rats for trials. He was also able to show that blood pressure could be reduced in salt-sensitive rats by adding potassium – a therapy still routinely used in hypertensive people today.

Pressure points

High blood pressure, or hypertension, is as much about fashion as medicine. Over the years, the threshold has steadily been dropping, and what was once considered normal is now dangerous.

Today, high blood pressure is any reading above 140/90 mmHg (millimeters of mercury), where the first number refers to systolic pressure, when the heart is pumping, and the second to diastolic pressure, when the heart is resting between beats.

The blood pressure values (in mmHg) below are general rule-of-thumb guides, as age, race, weight, gender and lifestyle also play a part in determining overall health.

• Normal: below 120/80

• Prehypertension: 120/139

• Stage 1 hypertension: 140–159/90–99

• Stage 2 hypertension: 160+/100+

• Hypertensive crisis (emergency): 180+/110+

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