Monday August 18, 2014
BY GENE EMERY
High salt is bad, but is less good? Researchers are divided. - Filepic
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While most scientists agree that high sodium intake is bad, new studies spark debate on further decreasing salt intake.
In one study that looked at death and heart disease, researchers found that extremely low-salt diets may not be as beneficial as many experts believe, and might even pose a hazard.
Another study, focusing on blood pressure effects, found that people with a moderate salt intake didn't benefit from reducing their consumption as much as people in the high-salt group.
“Previously it was believed that the lower you go the better. What these studies show collectively is that there is an optimal level, and lower is not necessarily better,” says Dr Andrew Mente of McMaster University in Hamilton, Ontario, chief author of the blood pressure study.
Salt is everywhere, in condiments such as your favourite kicap. It makes sense to know where your sodium is coming from. – Filepic
On the other hand, a third international study supports the conventional wisdom that there’s a direct link between less salt and better health. This study found no evidence that extremely low levels of sodium are dangerous.
One thing the three studies agree on is that too much salt is bad for you. High amounts contribute to high blood pressure, stroke, heart attack, kidney problems and heart failure.
That third study concluded that high salt intake was responsible for 1.65 million heart disease deaths worldwide in 2010.
“These are staggering numbers when you actually think about it,” says Dr Elliott Antman, president of the American Heart Association.
Worldwide, daily consumption is usually 3-6g of sodium, which translates to 7.5-15g of salt. That’s well above the limit of 1.5-2.4g of sodium each day recommend by the World Health Organization and other organisations.
“Even at 4g per day, we found half a million deaths per year,” says chief author Dr Dariush Mozaffarian, dean of the Friedman School of Nutrition Science and Policy at Tufts University. Mozaffarian says his analysis uncovered no danger at low levels or below, and he argued that even Mente’s blood pressure study showed no risk there.
However, Mente says the relationship seems to be more complicated than previously thought, and the health benefits of lowering salt intake don’t fall at the same place for everyone.
Experts are divided on how low salt intake should go and if that has an impact of health. – Filepic
“If people are eating a very high level of sodium and they reduce their intake, you get a large reduction in blood pressure,” he says. “But if you’re eating a moderate level of sodium and you reduce it to a lower level, you’re not really getting much in return as far as blood pressure reduction is concerned.”
The most dramatic evidence was the study that looked at the link between sodium intake and death, heart attacks and strokes using urine samples to estimate sodium consumption.
Led by Mente’s colleague at McMaster, Dr Martin O’Donnell, it found that consuming less than 3g of sodium per day increased the risk of death or major cardiovascular events by 27% compared to people who consumed 4-6g daily. The optimum sodium level was 3-6g per day. “Both higher and lower levels of estimated sodium excretion were associated with increased risk,” the O’Donnell team concluded.
That study shows “there are unintended consequences of going lower” adds Mente.
Currently only about 1% of people worldwide “were consuming less than 2g per day,” he says. “What we’re recommending right now is what almost nobody around the world eats, apart from maybe a few hunter-gatherer societies. We’re making recommendations where the human experience is extremely sparse. These findings strongly question our current recommendation.”
A sprinkle here, a dash there, scientists do agree that the current sodium intake is too high. – Filepic
Mozaffarian disagrees. Both the O’Donnell and Mente studies derived their results from the same research project, known as the PURE study.
“When you have a single study like the PURE study, that’s one study in the context of many,” says Dr Mozaffarian. Some have suggested a risk for very-low salt intake while others have not.
Not only does the weight of the evidence suggest that there is no risk in aggressive salt reduction, Mozaffarian says, “You don’t have any plausible biology to explain why you’d get a small increase in risk with low sodium intake.”
There’s another reason for scepticism. The PURE study assessed sodium consumption based on a single urine sample collected each morning. Antman called that a “very unreliable method” for measuring salt intake.
“The gold standard is 24-hour urine collection, and they didn't use it. And even then your sodium intake may vary a lot from day to day,” he says.
“The bottom line is, the American Heart Association’s position has not changed in response to the PURE paper,” says Antman, a cardiovascular expert at Brigham and Women’s Hospital in Boston. The association recommends less that 1.5 grams of sodium daily.
Nonetheless, Dr Suzanne Oparil of the University of Alabama at Birmingham contends in a journal editorial that, “Both high and low levels of sodium excretion may be associated with an increased risk of death and cardiovascular-disease outcomes and (the tests suggest) that increasing the urinary potassium excretion counterbalances the adverse effect of high sodium excretion.”
That idea should be confirmed in a large study, she said, but “in the absence of such a trial, the results argue against reduction of dietary sodium as an isolated public health recommendation.”
“The big picture is that high sodium is bad and should be reversed, and there’s just some controversy over how low you should go,” said Mozaffarian.
“Whether it should be 2g or 1.5g or 2.5g per day, that’s all theory,” he says. “Right now it’s close to 4g per day. Let’s get it down below 3, and then we can argue how low it should go. But right now it’s clearly way too high.” – Reuters
At the end of the day, the point to remember is that excess salt is not good for health.
