A deadly ingredient in our food
It makes everything taste delicious.
It has also been called "the single most harmful substance in the food supply".
A new paper by Harvard attributes excess salt consumption to 1.65 million deaths annually worldwide.
The study, published in the New England Journal of Medicine (NEJM), looked into cardiovascular deaths occurring in 2010 and attributed nearly one in 10 to sodium intake above 2 grams a day.
In what was termed a 'herculaen effort' to collate data from 66 countries, the study does have its limitations. Authors acknowledged it cannot prove that sodium restriction reduces cardiovascular mortality and noted that 'precise targets' for sodium reduction remain controversial.
In New Zealand, the recommended daily intake of sodium is between 1 to 2.3 grams. That means a teaspoon of salt is the upper limit. But what we're actually having is one-and-a-half times that amount.
While we need salt for survival, and for our body cells to function, there is a Goldilocks principle with salt.
Too little or too much and we are in trouble.
And exactly how much is just right is arguable.
"In the most general terms, getting less sodium [the problematic component of salt] in the diet lowers blood pressure," says the Harvard Medical School. "But how sodium reduction affects an individual depends on his or her genes, age, and medical conditions."
New studies, including the Harvard one, have attempted to detangle the complex salt-health relationship.
A second study, also published in NEJM, found those who consumed about half to one teaspoon of salt a day had "a lower risk of death and cardiovascular events than was either a higher or lower estimated level of intake".
Interestingly, a diet rich in potassium (found in beans, bananas, dark leafy greens and even potatoes) seemed to counter the harmful effects of salt.
A third study, which did not find a clear link between salt intake and blood pressure, found similar effects with potassium.
The authors suggested that instead of an aggressive campaign for the public to reduce salt intake, recommending a potassium-rich diet might have greater health benefits.
"Taken together, these three articles highlight the need to collect high-quality evidence on both the risks and benefits of low-sodium diets," wrote University of Alabama vascular specialist Dr Suzanne Oparil in an op-ed in the NEJM.
So while the experts work on the high-quality evidence, where does that leave the rest of us?
Kiwis like their salt
National nutrition advisor for the Heart Foundation, Delvina Gorton, says although we need small amounts of sodium in our diet, the amount is "really small compared to what we do eat".
The Heart Foundation wants us to take a lighter hand to the salt shaker, or ditch it altogether, because there's already a lot of salt in the food we're eating - without us adding to it.
"We know that most people's salt intake comes from processed foods. About three-quarters of the salt we eat is salt that's already added into food when we buy it," says Gorton.
One of the worst offenders is bread.
"Because we eat a lot of bread, it is actually one of the major contributors to our salt intake, whereas there are a lot of other foods that are higher in salt but we don't eat as much of them."
Gorton says there's a lot of work going on behind the scenes with food manufacturers, to cut the amount of salt we eat. The food industry is where we need to make the 'first and biggest' change.
"We know manufacturers can gradually reduce the amount of salt in food, and people's tastebuds won't really pick it up," she says.
"Some companies are taking it on board and have made some good reductions. But we have such a difference between where we are and where we need to be, that this needs to be accelerated right across the food supply."
She says to get our salt intake down, everyone needs to make a commitment - people need to make changes to food choices.
"To actually get to the target, it means cutting down on foods high in salt, eating less processed food and increasing our intake of fruit and vegetables."
Hypothetical modelling work done in New Zealand suggests that reducing sodium levels in manufactured foods by 25% would reduce the risk of heart disease by 21%.
"We do have a big reduction to make but it's an important one," says Gorton. "And if we do get wide-scale support from industry, we can definitely get there."
- Sydney Morning Herald & Stuff.co.nz