LONDON Reducing salt in the diets of the general population may not have an overall positive health impact, according to a review of more than 160 scientific studies published Wednesday.
In an analysis that fuels a row over the health effects of salt, researchers writing in the American Journal of Hypertension and the Cochrane Library journal said the systematic review added to growing evidence suggesting officials should re-evaluate policies advising everyone to eat less salt.
The review -- which collated and analyzed the findings of 167 previous studies -- found that while cutting down on salt reduced blood pressure in people who have normal or high blood pressure, it also caused increases in some hormones and other compounds that can adversely affect people's heart health.
"I can't really see, if you look at the total evidence, that there is any reason to believe there is a net benefit of decreasing sodium intake in the general population," said Niels Graudal of Copenhagen University Hospital in Denmark, who led the review and spoke to Reuters in a telephone interview.
Lowering salt intake is known to reduce blood pressure, but research has yet to show whether that translates into better overall heart health in the wider population.
Despite that, many countries have government-sanctioned guidelines calling on people to cut their salt or sodium intake for the sake of their longer-term health.
High blood pressure, or hypertension, is one of the leading causes of strokes, heart attacks and other cardiovascular diseases, which together are the biggest killers worldwide and claim more than 17 million lives a year.
"The question is not 'should' we reduce salt intake, but 'how'," said Graham MacGregor, a professor of cardiovascular medicine and chairman of the World Action on Salt campaign group, who said he strongly disagreed with Graudal's findings.
The World Health Organization (WHO) lists reducing salt intake among its top 10 "best buys" for reducing rates of chronic disease.
Franceso Cappuccio, Head of the WHO Collaborating Center for Nutrition at the University of Warwick, agreed with MacGregor and said Wednesday's study "should not distract our attention for implementing salt reduction policies at population level globally, as directed by national governments, the World Health Organization and the United Nations."
But a series of studies looking at dietary salt have recently suggested the evidence base for population-wide salt-reduction policies may not be as strong as first thought.
A separate Cochrane Library review conducted by British researchers and published in July found no evidence that small reductions in salt intake lowered the risk of developing heart disease or dying prematurely.
And another study by Belgian scientists published in May found that people who ate lots of salt were no more likely to get high blood pressure, and were statistically less likely to die of heart disease, than those with low salt intake.
Graudal said his results showed that when salt intake is reduced, there are increases in some hormones and in fats known as lipids "which could be harmful if persistent over time."
He added that because none of the studies in the review were able to measure long-term health effects, his team was not able to say "if low salt diets improve or worsen health outcomes."
Graudal said the growing number of studies questioning the net benefit of salt reduction meant public health officials should look again at their guidelines.
Current government advice in Britain calls for an acceleration of the reduction in salt intake by adults from a maximum of 6 grams (g) a day by 2015 to 3g by 2025.
U.S. dietary guidelines recommend Americans consume less than 2.3g of sodium daily, or 1.5g for certain people who are more at risk of high blood pressure or heart disease. A teaspoon of salt, or roughly 5g, holds around 2.3g of sodium.
MacGregor disputed Graudal's conclusion about the lack of a net benefit and said the review "clearly shows once again that decreasing salt intake lowers blood pressure."
"This study, contrary to the authors' claims, supports the wealth of evidence that reducing our salt intake will be immensely beneficial in preventing strokes, heart attacks and heart failure," he said in a statement emailed to Reuters.
(Editing by Elizabeth Piper and Andrew Heavens)