Experts who say you can DOUBLE your daily SALT limit
SHOULD a pinch of salt be back on the table? A study published recently in the Lancet suggests it should, with researchers advising that consuming up to two-and-a-half teaspoons (12.5g) of table salt a day is not only safe, it’s positively good for you.
As the official advice is to have no more than 6g of salt a day, this may sound like heresy. In fact, this controversial study represents the latest sally in a heated debate over salt that has divided medical researchers for decades.
The study, from McMaster University in Ontario, Canada, was based on the sodium levels of around 95,000 people in 21 countries, along with data on whether they suffered heart attacks or strokes over the following five to nine years. (Sodium makes up 40% of salt; the rest is chloride.)
A very high salt consumption (more than 12.5g) is ‘most certainly associated with increased risk of stroke and heart disease, at least in people with high blood pressure,’ says the lead researcher, Professor Andrew Mente, an epidemiologist at the Population Health Research Institute at McMaster University.
However, eating ‘too little salt’ (less than one-and-a-half teaspoons, 7.5g) daily may be equally dangerous.
‘The vast majority of people globally have an average sodium intake of between 3g and 5g a day [between 7.5g and 12g salt] — that’s the amount of salt most people seem to like in their diets,’ Professor Mente tells Good Health.
‘Our study adds to growing evidence which suggests that, while this moderate level of sodium does increase blood pressure somewhat, it’s actually good for heart health.’
The researchers say this is in line with a previous review of studies published in the journal Frontiers in Physiology in 2016, which suggested that those at lowest risk of cardiovascular events consume one-and-a-half to two-and-a-half teaspoons of salt a day.
In other words, the official daily maximum salt intake of 6g could, according to this research, actually raise your risk of premature death because it’s too low.
OUR bodies definitely need sodium — it plays a key role in enabling muscles to contract, transmitting nerve impulses and maintaining hydration. Where scientists disagree is on the amount of sodium that’s healthy. The advice of the world’s health organisations and government bodies is to limit salt to around 5g, or a teaspoonful a day.
This stems from a series of studies carried out from the Eighties onwards known as Intersalt (an international study of electrolyte excretion and blood pressure).
The research, conducted by US and British epidemiologists, measured salt intake in 10,079 people in 52 countries and showed that the more sodium there was in the bloodstream, the higher the blood pressure.
An influential paper published in the BMJ in 2007, based on data collected from three-quarters of the original participants, showed that after 15 years, the risk of a heart attack or stroke was more than 25% lower in people who had cut their salt intake for at least 18 months.
Salt draws water out of the body’s cells. So the more salt you eat, the more water is taken into the bloodstream, swelling the volume and increasing your blood pressure, explains Graham MacGregor, professor of cardiovascular medicine and chair of the pressure group Action on Salt.
‘Think of salt as you think of tobacco — except that salt is a bigger killer,’ Professor MacGregor tells Good Health. ‘Smoking kills seven million people globally every year, but high blood pressure kills 30 million. And taking salt out of your diet is one of the easiest ways to reduce blood pressure.
‘Over the past decade or so, we have seen a steady reduction in salt content in ready meals and processed food. That has been reflected in a reduction in cardiovascular disease and mortality. We cannot risk that progress now.’
The research published in the Lancet, known as the PURE (Prospective Urban Rural Epidemiology) study, is an even larger series of trials than Intersalt, based on the sodium consumption of 95,767 people in 18 countries (it tracked their health for up to nine years). ‘There’s no disagreement at all as to whether it’s safe to add more than two-anda-half teaspoons of salt to your food every day,’ Professor Mente tells Good Health. ‘We know it’s associated with increased risk of stroke and heart disease in people with high blood pressure.
‘We also showed that while very low sodium intake will reduce blood pressure even further, it actually ceases to be beneficial.
‘Consuming less than 2g of sodium a day [5g, or one teaspoon, of salt] appears to have other effects, including raising levels of hormones that are associated with an increased risk of death and cardiovascular disease.’
Excessively low levels of sodium can also cause nausea, headaches, dizziness and fatigue — and, more seriously in the long-term, kidney or heart failure.
The PURE team argue that, rather than lecturing people on cutting out salt, health authorities should focus on a further major finding: that the more potassium people eat, the greater the reduction in rates of stroke, heart disease and overall mortality.
Potassium, found in fresh fruit, vegetables and dairy foods, helps to lower blood pressure by blunting the effect of too much sodium: the more potassium we eat, the more sodium we pass out of the body in urine. ‘Our findings support recommendations for an all-round healthy diet with an emphasis on fruit, vegetables, dairy foods, potatoes, nuts and beans,’ says co-author Professor Martin O’Donnell of the Department of Medicine at McMaster University.
COMMENTING approvingly on the PURE research in a Lancet editorial, Franz Messerli, professor of medicine at the University of Bern in Switzerland, suggests the harmful effects of even very high levels of sodium consumption may be cancelled out as long as salt lovers eat healthily.
It is worth noting, he says, that women in Hong Kong top life expectancy worldwide, with an average lifespan of 87.3 years, despite consuming on average 8g to 9g salt a day.
‘We don’t have the proof as yet,’ he tells Good Health. ‘But there is a suggestion that where, as in Hong Kong, the cuisine is made of healthy, potassium-rich fresh food, then salt and its main ingredient, sodium, is not a problem.’ But critics of the PURE research say it is unscientific and must be ignored. Professor Francesco Cappuccio, chair of cardiovascular medicine and epidemiology at the University of Warwick, accused the Lancet of publishing ‘flawed’ data.
The study, he claimed, ‘is not fit to address any of the issues regarding salt consumption’.
At the heart of this dispute is the problematic business of measuring salt intake. The only reliable method is to test urine but the experts are at odds about collection methods.
The ‘gold standard’ and most popular method is to test urine collected over a 24-hour period.
Yet a simpler approach that makes large global trials affordable, adopted by PURE, is now claimed to be good enough science —collecting a single midstream sample from each participant and subjecting it to a complex mathematical formula that, it is claimed, can produce reliable information about sodium intake.
The debate continues.