To Salt Or Not To Salt: That Is The Question

"We thought, 'That's peculiar'. Then we sat on that data for two years. We did everything we could to make it go away and we couldn't make it go away no matter how you analyze the data."

"The bottom line is, if low sodium is not helpful and may even increase the risk, it's better to focus on the overall quality of the diet."

"Reduce processed foods and focus on eating more fruits and vegetables and more potassium-containing foods -- an all-around wellness diet."

Professor Andrew Mente, epidemiology professor, McMaster University, Hamilton

Crystals of table, kosher, and pickling salt   (AP / Nati Harnik)

 

In reflection of conventional wisdom respecting the place of salt in a diet therapy meant for people with high blood pressure, the World Health Organization recommends consumption of less than two grams of sodium (five grams of salt) daily. The Mayo Clinic and Health Canada along with other health bodies suggest no more than 2.3 grams (about a teaspoon of salt) daily. In Canada, a report issued in 2017 by Health Canada assessed the average intake per person of salt in the country to be 2.8 grams.

Studies like the Harvard University-led TOHP trial in the United States in late 1980s and early 1990s underpin such recommendations from within the international health community. In that study some 4,500 people were divided into groups receiving either general healthy lifestyle advice or alternately weekly group and individual counselling in reducing sodium intake. Leading to the conclusion that those who received salt-reduction assistance were 25 percent less likely to suffer strokes, heart attacks and other cardiovascular events in years to follow.

Other controlled studies reached like conclusions; that as people absorb less sodium, a reduction in hypertension resulted, according to a recent paper. And then in 2009 Dr.Salim Yusuf of the Population Health Research Institute (PHRI) of McMaster University and Hamilton Health Sciences published research and commentaries that suggested heart health did not improve with sharp salt reduction intake. To state that consternation, condemnation and confusion and controversy resulted is to understate the impact of this reversal of popular medical wisdom.

Dr.Yusuf and his team of researchers made the decision to study the issue relating to two studies they ran focused on testing blood pressure drugs. A sidebar sodium study enrolled about 28,000 people from 40 countries. The participants, all at risk of cardiovascular disease, had their intake of sodium measured through interpreting secretions of the mineral in urine samples. What this study revealed shocked the scientists when they found that as sodium levels fell the rate of heart-and-stroke-related illness did initially fall, then rose again, with sodium intake amounts lower than three grams daily.

 

High blood pressure leads to heart attacks, strokes and death. Hypertension is considered the world's leading cause of mortality, and sodium considered the culprit in up to 30 percent of cases. The greater the sodium intake, the greater the retention of water in the body, to wash it away. This increases the pressure of blood being pushed through arteries and veins. Not only did cutting sodium below a certain point not lead to improved cardiovascular health, lower levels it turned out, might in fact increase risk of disease.

After the results were published in some of the world's foremost medical journals, and the McMaster University research team led by Dr.Yusuf, a highly respected researcher, were castigated for their unacceptable findings, they followed up with a parallel study of 102,000 subjects from 17 countries in another McMaster-led international research project called PURE. Published in the high profile New England Journal of Medicine, the results for the second study were similar to the earlier ones.

Their conclusion led them to argue the earlier evidence, like the TOHP trials, did not indicate that the standard sodium diet-reduction to the recommended level had any effect on improving health outcomes. Their critics focused on what they found to be a flaw in the methodology of the study where the gold-standard method is to collect all urine someone produces in a 24-hour period to test for secreted sodium and repeat it on non-consecutive days, whereas the McMaster-led trial performed a single fasting (spot sample) of urine early morning.

"It's tough and it's tedious so people try to cut a lot of corners (24-hour sampling). With a single-spot sample] stuies are much easier to do, much less complex -- and give you the wrong answers", pointed out Dr.Norman Campbell of University of Calgary. "They're making inaccurate and false statements and misleading statements and misinterpretations and they're not correcting things that are obviously flawed. this is a global aggravation for people who are trying to improve the health of their populations."

 

Dr.Mente, on the other hand, speaks of the advice to maintain sodium intake no higher than four or five grams daily, and not to be concerned about cutting it much below three grams. He also pointed out that their sodium studies were subjected to intense peer review pre-publication, where prominent journals assign vetting to half a dozen scientist-reviewers and two statisticians to vouch for accuracy. 

 

Dr.Yusuf comments that the science is in flux and the research he and his team conducted has aided in altering the sodium-hypertension paradigm; that their critics are unwilling to consider that health and research understandings have undergone an alteration. He and his colleagues' study results have come under scrutiny with charges of bias resulting from study funders such as health charities and drug companies.

"[Campbell's] enthusiasm for this as a crusader, you have to admire it."

"But at the same time, all scientific debate has to be based on respect, it has to be based on openness."

"It has to be based on entertaining different viewpoints."

Dr.Martin O'Donnell, professor of medicine, National University of Ireland, Galway, McMaster group collaborator

Relying on the conventional scientific wisdom, the World Health Organization recommends consuming less than two grams of sodium — five grams of salt — a day. Health Canada, the Mayo Clinic and other health bodies suggest no more each day than 2.3 grams, about a teaspoon of salt. Photo by Getty

 

"A new controversial study claims that in most cases, consuming salt will not increase health risks. The study published on August 9 in The Lancet, a scientific journal, followed 94 000 people between the ages of 35 and 70 across 18 countries to determine whether salt intake truly does increase the risk of cardiovascular disease and stroke (1), an accepted belief. Monitoring subjects over an average span of eight years,  interestingly, it was found that the risk only increases if the average sodium intake is greater than 5 g per day ― the equivalents of 2.5 teaspoons of salt."

"The research was led by Prof Salim Yusuf of the Population Health Research Institute (PHRI) of McMaster University and Hamilton Health Sciences in collaboration with colleagues from 21 different countries, including Canada, Argentina, Bangladesh, Brazil, Chile, China, Columbia, India, Iran, Malaysia, occupied Palestinian territory, Pakistan, Philippines, Poland, Saudi Arabia, South Africa, Sweden, Tanzania, Turkey, United Arab Emirates, and Zimbabwe."

"Salt-reduction enthusiasts argue that campaigns in the UK, Japan, and elsewhere over the past several years have led to a reduction in salt intake and consequently, a reduction in overall average blood pressure of the population. However, our bodies require essential nutrients like sodium to function, therefore, completely removing salt from our diets may be just as damaging as too much. But the question remains, how much is too much?"

European Scientist