Is a low-salt diet harming your heart?
Since 1969, we’ve been advised to consume less salt.
Since then, nutritional science has progressed significantly and guidelines – including recommendations around fat and artificial foods like margarine or sugar substitutes – have done back-flips.
An extensive new study, involving more than 130,000 people from 49 countries, has raised questions about whether the recommendations around salt intake also need to change.
The study, published in respected journal, The Lancet, found that cardiovascular disease and premature death were increased with low salt intake for those with both normal and high blood pressure.
On the flip side, the risk of cardiovascular disease and premature death only increased when individuals with high blood pressure consumed more than 7 grams of salt per day. There was no increased risk for those without high blood pressure.
“While our data highlights the importance of reducing high salt intake in people with hypertension, it does not support reducing salt intake to low levels,” said McMaster University’s Andrew Mente, lead author of the study.
“Our findings are important because they show that lowering sodium is best targeted at those with hypertension who also consume high sodium diets.”
To put this in perspective, according to the World Health Organisation, a ‘high’ salt intake is more than 5 grams (one teaspoon is about 6 grams) of salt per day.
The current Australian guidelines are 1.15–2.3 grams of salt per day, however most Australian adults have a daily salt intake of about 10 grams.
“This study adds to our understanding of the relationship between salt intake and health, and questions the appropriateness of current guidelines that recommend low sodium intake in the entire population,” said study co-author Dr. Martin O’Donnell.
Salt issue settled. Except it’s not.
“It’s a huge study so one has to give some credibility to it… a tour de force,” admits Professor Robert Graham, executive director of the Victor Chang Cardiac Research Institute.
“But it’s still an observational study and there are always limitations on observational studies.”
In an editorial response to the study Eoin O’Brien, from University College Dublin, agreed.
“Although large prospective observational studies give supportive evidence, they do not prove causality,” he wrote.
Graham further explained that there may be other explanations for the increase in cardiac problems in the low salt group.
“Nutritional studies are notoriously difficult. Unless you stand over [participants] and measure everything they eat,” Graham said, “some days we eat more salt than others.”
Graham notes previous research on the Yanomamo Indians, whose native diet is very low in salt and whose blood pressure does not rise with age nor do they develop vascular disease.
However, according to a paper analysing the link between salt and blood pressure, when the the Yanomamo migrate and adopt a western lifestyle, they become overweight and develop diabetes and premature vascular disease.
“There are other similar examples which clearly indicate that cardiovascular disease (strokes, heart attacks and heart failure) could be entirely prevented if we changed our diet and lifestyle,” the paper concludes.
How much it is possible to separate salt from other ‘western lifestyle’ factors?
“More processed food tends to be high in salt as opposed to adding it to fresh food yourself when you know exactly how much you’re adding,” Graham says.
He adds of the new latest study:
“It’s a difficult issue but an important one. The jury is still out. If you’ve got high blood pressure, limiting salt is good. But the question is whether limiting it in people with normal blood pressure is good.”
What is high blood pressure?
According to the High Blood Pressure Research Council of Australia (HBPRCA), there are various definitions of high blood pressure, which is also known as hypertension, but most doctors consider blood pressures of more than 140/90 to be high. About 20 per cent of Australians have high blood pressure, which affects the risk of heart attack and stroke.
Changes to lifestyle such as weight loss, reduced salt intake, reduced alcohol consumption or exercise are often the first line of treatment, the HBPRCA explains. If these approaches don’t return blood pressure to acceptable levels then drug treatment is usually required.
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