May 24 2016 Posted: 09:18 IST

NUI Galway Academic is co-author of global study which finds salt is essential to a person’s health and reduction matters most in people with high blood pressure who consume high salt diets

A large worldwide study involving 49 countries has found that, contrary to popular thought, low-salt diets may not be beneficial and may actually increase the risk of cardiovascular disease (CVD) and death (compared to average salt consumption). The results from the study were published in The Lancet.

The study, involving more than 130,000 people from 49 countries, was led by investigators of the Population Health Research Institute (PHRI) of McMaster University and Hamilton Health Sciences.

Professor Martin O’Donnell, a co-author on the study and an associate professor at NUI Galway, said: “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. Our findings highlight the need for a definitive clinical trial that determines the safety and effectiveness of sustained low sodium intake on incidence of heart attacks and stroke.  Until definitive trials are completed, an approach that recommends salt in moderation, particularly focused on those with hypertension, appears more in-line with current evidence.”

The researchers looked specifically at whether the relationship between sodium (salt) intake and death, heart disease and stroke is different in people with high blood pressure compared to those with normal blood pressure. The results showed that regardless of whether people have high blood pressure, low-sodium intake is related to more heart attacks, strokes, and deaths compared to average intake.

“These are extremely important findings for those who are suffering from 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. Our findings are important because they show that lowering sodium is best targeted at those with hypertension who also consume high sodium diets,” said Dr Andrew Mente, lead author of the study, a principal investigator of PHRI and an associate professor of clinical epidemiology and biostatistics at McMaster University’s Michael G. DeGroote School of Medicine.

Current intake of sodium in Canada is typically between 3.5 and 4 grams per day and some guidelines have recommended that the entire population lower its sodium intake to below 2.3 grams per day, a level that fewer than five per cent of Canadians and people around the world consume.

Previous studies have shown that low-sodium, compared to average sodium intake, is related to increased cardiovascular risk and mortality, even though low sodium intake is associated with lower blood pressure. This new study shows that the risks associated with low-sodium intake – less than three grams per day was consistent regardless of a patient’s hypertension status.

The findings show that while there is a limit below which sodium intake may be unsafe, the harm associated with high sodium consumption appears to be confined to those with hypertension. Only about 10 per cent of the population in the study had both hypertension and high sodium consumption (greater than 6 grams per day).

Dr Mente said that this indicates that the majority of individuals in Canada and most countries are consuming the right amount of salt and suggests that targeted salt reduction in those who are most susceptible (those with hypertension and high salt consumption) may be preferable to a population-wide approach to reducing sodium intake in most countries except those where the average sodium intake is very high, such as parts of central Asia or China.

He added that what is now generally recommended as a healthy daily ceiling for sodium consumption appears to be set too low, regardless of a person’s blood pressure level.

Dr Mente continued: “Low sodium intake does reduce blood pressure modestly, compared to moderate (or average) intake, but low sodium intake also has other effects, including adverse elevations of certain hormones associated with an increase in risk of death and cardiovascular diseases. The key question is whether these competing physiologic effects result in net clinical benefit or not.”

The study was funded from more than 50 sources, including the PHRI, the Heart and Stroke Foundation of Canada and the Canadian Institutes of Health Research.

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