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Are low-salt diets bad for your heart? This Canadian study is stirring up controversy

Are you eating too much salt? How about too little?.
Are you eating too much salt? How about too little?. THE CANADIAN PRESS/AP-Larry Crowe

Health officials have worked tirelessly to get the public to cut back on their salt intake. But a new Canadian study is warning that, contrary to popular thought, a low-salt diet may not be benefiting your health – it might even increase the risk of heart disease in some people.

Scientists out of McMaster University in Hamilton, Ont., suggest that a low-salt diet is linked to more heart attacks, strokes and heart disease-related deaths compared to a diet that includes average sodium intake.

Their findings are controversial but they’re based on a global study that looked at more than 130,000 people from 49 countries.

“[Our study] shows that low-salt diets may not be beneficial to anyone and high-sodium diets are harmful only to people with high blood pressure,” lead researcher, Dr. Andrew Mente, told Global News.
“The people who have normal blood pressures tend to be more salt resistant, and they have very little change in blood pressure. [Cutting back on salt] is only for people who are salt sensitive. It’s not one size fits all,” he explained.

READ MORE: Hold that salt! Top 5 foods packed with sodium

Mente is an assistant professor in clinical epidemiology at McMaster.

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He said that in recent years, health officials have been on a crusade to cut back on salt in consumers’ diets and within the food industry. But there’s another side to the story, too: a low-sodium diet isn’t for everyone and previous studies have pointed to health harms from it.

Canadians eat about 3,400 milligrams of sodium daily – that’s more than double the amount that we need. We need sodium to help us keep the right balance of fluids in our bodies; it aids in transmitting nerve impulses and with our use of muscles.

But too much salt has been tied to high blood pressure, a major risk factor for stroke, heart disease and kidney disease.

The study is based on pooled data from four different studies. Of the 130,000 people, only about 10 per cent of the population had both hypertension and a high-salt diet that was greater than six grams – or 6,000 milligrams – per day.

READ MORE: Top 10: Some of the worst foods for your heart’s health

But people who were on a low sodium diet – eating less than three grams per day – saw a risk of heart disease even if they weren’t dealing with hypertension.

Mente suggests that a too-salty diet is only a danger for people who are already dealing with high blood pressure or are predisposed to it.

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Those who have a normal blood pressure and aren’t “salt-sensitive” can consume above the recommended limits without the same risks, he said.

With that in mind, he suggests that low-sodium diets need to be targeted to those living with hypertension or at a greater risk of it.

READ MORE: 5 lifestyle changes to improve your heart’s health

“Based on the data, if you’ve got a normal blood pressure, even higher amounts of sodium are not related to harm. It’s just generally good to know that an all-around healthy diet would be optimal and you don’t need to worry about sodium,”  Mente told Global News.

The study was published in the prestigious medical journal, The Lancet, last Friday.

According to the Independent in the United Kingdom, critics are slamming the journal for publishing “such bad science.”

Dr. Francesco Cappuccio, head of the World Health Organization’s Collaborating Centre for Nutrition, told the UK outlet that he didn’t agree with the study’s methodology and bottom line.

The study measured salt intake by a single urine sample test given in the morning. The study participants were also “almost exclusively from clinical trials of sick people that have a very high risk of dying and are taking several medications,” Cappuccio said.

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He said these are “glaring” errors the Lancet should have picked out.

“The evidence supporting global actions for a moderate reduction in salt consumption to prevent cardiovascular disease is strong and such studies should not overturn the concerted public health action to reduce salt intake globally,” he told the Independent.

READ MORE: Salt levels in fast food ‘substantially’ higher in Canada, according to a new report

(For its part, the Lancet published commentary to accompany the study. In it, an expert said that a single urine test should suffice for a “valid measure” of average salt intake.

“It should come as no surprise that a low-salt-for-all policy would benefit some and disadvantage others,” the commentary said.)

Dr. Frans Leenen, is director of the Hypertension Clinic at the University of Ottawa Heart Institute, where he’s also a professor of medicine and pharmacology.

For years, he’s studied different levels of salt intake and their effects on blood pressure.

He suggests that those who are salt-tolerant now may not be down the road. Keeping your salt intake in moderation – as in, not too much and not too little, regardless of age – will pay off.

“Many people have normal blood pressures to start with and when you’re 50 or 60 you will develop hypertension. If your blood pressure happens to be salt sensitive down the road, you could delay the development of salt intake but you may not be able to prevent it,” Leenen explained.

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READ MORE: Will the Paleo diet make you fat? Why this controversial study is angering diehard supporters

The findings “confirm” the relationship between salt intake and blood pressure varies based on your blood pressure to start with, he suggests.

“What they’re showing is if you have a high blood pressure and salt intake is well above average, you have an increased risk of cardiovascular disease. The people within normal blood pressure see a fairly modest, if any, effect,” he said.

Most Canadians don’t need to worry, Mente said. If you’re eating a healthy diet without too much fast food or processed fare, it’s very likely you’re not overloading or underdoing on salt.

The study was funded by more than 50 different organizations, including the Heart and Stroke Foundation of Canada and the Canadian Institutes of Health Research.

Read the full study.

carmen.chai@globalnews.ca