A recent study published in medical journal The Lancet on May 20, 2016, has found that people who consume low salt levels have an increased risk of heart attacks, strokes and death, no matter if they are hypertensive or not. People who have high salt levels also share the same risk but only if they have high blood pressure issues.
The study was funded by multiple sources with the most prominent being the Heart and Stroke Foundation of Canada, Canadian Institutes of Health Research, and the Population Health Research Institute (PHRI).
Researchers at PHRI, McMaster University and Hamilton Health Sciences Canada, analyzed the data of 133,118 individuals from 49 countries, of which 63,559 had hypertension. The data was extracted from four large prospective studies and originally calculated from the morning fasting urine samples obtained from the participants.
The data showed that the lowest risk of adverse heart events was in people who consumed moderate amounts of salt (4g or 5g), as compared to those who consumed low salt levels (3g a day) or high levels of salt (7g or more). People with low salt levels were diagnosed with hypertension had an 11% chance of death or of a serious cardiovascular mishap.
Andrew Mente, an associate professor of clinical epidemiology and biostatistics at McMaster’s Michael G DeGroote School of Medicine and the lead author of the study, explained that these findings are highly significant for people with hypertension. The findings suggest promoting low salt levels in people with hypertension but do not support reducing salt intake levels in people without hypertension. He suggested that low salt levels are best advised for people with hypertension, who also have high salt intake levels.
The study found that out of the total participants, 10% had both high salt intake levels and diagnosed hypertension.
Martin O’Donnell, coauthor and associate clinical professor at McMaster University and National University of Ireland, Galway, also backed the findings and said that the study provides new understanding into the subject and ‘questions the appropriateness’ of current guidelines of recommending low salt intake levels for the whole population.
Dr Mente suggested that compared to the current approach adopted by almost all of the countries, which suggests lowering salt consumption level in all of the population, a better approach would be to target people with high blood pressure.
The Scientific Community Comments
The study has garnered much critique since its publication. Professor Francesco Cappuccio, from the World Health Organization Collaborating Centre for Nutrition and University of Warwick, termed the research as ‘bad science’, openly showing his disbelief and criticizing the highly acclaimed journal for publishing this research.
Dr Cappuccio pointed out that the study used mathematical models which were not adequate enough to give an accurate reading. The patients in the study were quite sickly, on multiple medications and already at risk of death. The study, according to him, was also not unique and based on previous similar studies. According to him, the large size of the participants in the current study just increased the chances of more compound errors.
He further added that the evidence for the blanket ‘low salt levels for all’ policy is strong and studies like these should not overturn the already implemented action plan for ‘reducing salt intake globally’.
Chairman World Action on Salt and a professor at Queen Mary University, Dr Graham MacGregor agreed with the assessment of Dr Cappuccio and said that this study ‘does not in any way overturn public health messages to reduced salt intake, both in UK and worldwide’.
American Heart Association came out with an opinionated comment piece on the study where two presidents of the association gave their opinion on the subject.
Director Heart and Vascular Center at Dartmouth-Hitchcock Medical Center, Dartmouth College and President of American Heart Association, Mark Creager, found it ‘worrisome’ that the study may reverse the progress made in modifying sodium intake and reducing the risk of hypertension. He stressed that people should understand that the current guidelines are based on well-founded research.
The former president of the association, Dr Elliot Antman, currently working at Harvard Medical School and as a physician in Cardiovascular Division of Brigham and Women’s Hospital in Boston, said that AHA continues to ‘maintain that no more than 1,500 milligrams of sodium a day is best for ideal heart health’.
CDC recommends that the citizens of United States should consume 2,300 milligrams of salt a day. NHS advises the use to be less than 6,000 milligrams per day. On the other hand, in Canada where the typical intake is between 3,500 to 4,000 milligrams per day, some recommendation guidelines suggest keeping the intake below 2,300 milligrams per day.
WHO notes that the current salt intake levels are at 9,000 to 12,000 milligrams per day in the world which is twice the maximum level of intake advised. The health agency advises to keep the level below 5,000 milligram and has brought on board all its member states to reduce the global salt intake level by a relative 30%, by the year 2025.