Take recent sodium studies with a grain of salt

The war on salt is, well, under assault.

Headlines in recent weeks have declared lower salt consumption may not be beneficial to our health. The federal government disbanded a task force that was supposed to oversee a national sodium-reduction strategy earlier this year. And last week, the incoming CEO of the Campbell Soup Company, which has been at the forefront of corporate efforts to cut sodium in food products, announced she had found a possible solution for flagging sales: adding salt back into the company's soups.

At first glance, it seems they have a good case for casting doubt on the long-held notion that too much sodium is a health hazard.

A widely publicized study that appeared in the May edition of the respected Journal of the American Medical Association suggested low-salt diets actually increase a person's risk of dying from heart disease. That was followed by a study published earlier this month in the American Journal of Hypertension; it found efforts to lower sodium have little effect on cardiovascular disease risk.

Countless blogs, social-media users and media reports have begun to question the crusade in many countries to persuade companies to cut the high amounts of sodium added to many food products. Scientific American summed up the backlash with an article this month titled "It's Time to End the War on Salt."

Providing fuel for the pro-sodium side is the Salt Institute, a Virginia-based advocacy group that has for years been touting the benefits of higher sodium consumption while warning recent efforts to cut salt could be hazardous for the population's health.

"There's no evidence that says we have to reduce, population-wide, our salt consumption," said Morton Satin, vice-president of science and research for the institute.

But look a little closer, and it appears that the notion of cutting sodium consumption may not be beneficial, or perhaps even cause health problems, is based on shaky evidence.

Take the May study in the Journal of the American Medical Association. It published the startling findings that people who eat lower amounts of sodium are more likely to die from cardiovascular disease and that, among those with normal blood pressure, sodium intake didn't lead to high blood pressure.

The findings received significant attention. But the fact the study had so many problems and flaws it prompted researchers from Harvard to respond by saying the conclusions "are most certainly wrong," received little notice.

The majority of study participants were in their early 40s when the research began and were only followed for about eight years – meaning the population was too young to accurately determine how sodium intake could affect their long-term health.

Meanwhile, the American Journal of Hypertension study was preceded by an attention-grabbing press release titled "Cutting down on salt doesn't reduce your chance of dying."

Researchers reviewed a series of previously conducted studies and found people who moderately reduced their sodium consumption didn't reduce their risk of dying or developing cardiovascular disease.

The findings "undermine the appealing (sic) assumption that the modest blood pressure fall caused by curtailing sodium intake will necessarily translate into cardiovascular protection," wrote Michael Alderman, editor-in-chief of the journal, in an editorial.

But medical experts highlight several criticisms, chiefly that one of the studies involved patients with heart failure, meaning the results aren't relevant to the general population. In addition, the studies only included about 6,200 participants, far too few to make sweeping conclusions about the health effects of sodium. People in the study also only reduced sodium intake by moderate amounts and were followed for relatively short periods, not enough to see a significant difference in a person's long-term health, experts said.

"It's been completely misinterpreted, unfortunately," said Kevin Willis, director of partnerships at the Canadian Stroke Network.

The study even warns the results could be misconstrued "depending on people's perspectives and circumstances."

Lead author Rod Taylor of the University of Exeter in Britain said the results actually demonstrate why wide-scale sodium-reduction efforts are needed.

"Indeed it is likely that participants in these studies initially followed advice to reduce salt, but were not able to maintain this in the long term which contributed to the lack of health benefit," Dr. Taylor said in a press statement.

So why did the study generate controversy for seeming to suggest less salt was a bad thing? Some experts look to the journal's editor-in-chief, Dr. Alderman, a long-time critic of sodium reduction, who wrote an editorial accompanying Dr. Taylor's study. Despite the fact he has worked as a consultant to the Salt Institute, Dr. Alderman did not declare the association as a potential conflict of interest in the editorial. He did not respond to a request for comment.

"From my perspective, this is about as sleazy as it gets," said Norm Campbell, one of the country's top sodium experts and Canada Chair in Hypertension Prevention and Control.

One thing people on both sides of the issue can agree on: The field could benefit from a large trial that compares people who follow low-salt diets and those who don't over a long period of time to see the results. But it's a tall order with huge obstacles standing in the way – namely, ensuring a large group of people adheres to a low-salt diet for decades.

"Those trials can't be done for practical considerations," Dr. Willis said.

Instead, he and other experts say there is enough clear, unbiased evidence demonstrating the potential health benefits of reducing salt, and the consequences of consuming excessive amounts for many years, which most Canadians do, to justify plans to cut sodium across the entire population.

"The overwhelming evidence is compelling," Dr. Willis said. "It favours sodium reduction."