These are the surprising symptoms linked to eating too much salt as research suggests high levels can cause a string of serious conditions
For more than 20 years, we’ve been bombarded with public health messages to reduce our salt intake in order to slash the UK death toll from heart disease.
The Government’s Scientific Advisory Committee on Nutrition first issued the advice in 2003, when the evidence that excess salt consumption could lead to dangerously high blood pressure became overwhelming.
The goal, experts declared, should be for everyone to eat no more than 6g of salt a day – little more than a teaspoonful – both from foods that already contain it and from salt added at the table.
But according to the British Heart Foundation, it’s a target most of us repeatedly miss. It estimates that most adults in the UK still eat around 8.4g of salt daily – 40 per cent above the maximum target.
The NHS website says this is mainly because three quarters of the salt we consume comes from packaged and processed everyday foods – such as bread, cereals and fast foods. In other words, it’s extremely difficult to avoid.
B ut now there may be added impetus to the salt-reduction drive following the publication of a series of studies linking high intake with depression, hearing loss and even dementia.
‘There has been a spate of studies linking excess salt intake with poor mental health,’ says Professor Matthew Bailey, head of the Centre for Cardiovascular Science at the University of Edinburgh, who has carried out animal research showing that salty diets trigger a surge in levels of stress hormones that can affect mood – a finding he believes could also apply to humans.
‘These studies show high salt intake over long periods of time is not just raising the risk of cardiovascular disease, but possibly also mental health problems and even dementia.’
When we eat too much salt, the kidneys detect that there are high levels in our bloodstream
Professor Matthew Bailey, head of the Centre for Cardiovascular Science at the University of Edinburgh
A certain amount of salt – or, more specifically, sodium chloride – is vital for the body’s essential functions, such as maintaining nerve signals and helping muscles contract. But we need to consume just 1-2g a day to fulfil the body’s needs.
Part of the problem is humans often crave it because, as Professor Bailey explains, our ancestors constantly had to seek out natural deposits – which were usually spread far and wide – in order to survive. That evolutionary desire remains, even though salt is now in plentiful supply.
And when we eat too much, the kidneys detect that there are high levels of salt circulating in the blood. In turn, they pull water out of other tissues and organs to pump into the bloodstream to keep salt levels balanced.
The extra volume puts pressure on artery walls – making them stiffer and narrower – while also making the heart work harder to push it round the body, pushing up blood pressure.
Over time, this increases the risk of heart attacks, strokes and heart failure – where heart muscle effectively wears out from all the hard work.
But while the link with heart disease is well established, salt’s potential influence on mental health and the brain is only now being unravelled.
In July, an analysis of data from more than 270,000 people on the UK Biobank – a huge database of health information – showed those who ‘sometimes’ added salt to their food were 20 per cent more likely to have a diagnosis of depression than those who never sprinkled it on their meals. Those who admitted ‘always’ adding salt were 45 per cent more likely to be depressed, reported the Journal of Affective Disorders.
The results are not a one-off. Earlier this year, research by Huazhong University of Science and Technology in China, which tracked 439,000 people over 12 years, found that those who always added salt were 37 per cent more at risk of depression – and 27 per cent more likely to have anxiety.
But why would this household condiment have such a dramatic impact on mood?
O ne theory is that it drives up production of IL-17A, an inflammatory protein that’s already known to play a part in pushing up blood pressure. In the brain, excess IL-17A activates inflammatory pathways and disrupts the normal balance of signalling chemicals that control mood.
Earlier this year, research on mice showed levels of IL-17A in the spleen, blood and brain jumped when they were fed a salty diet – as did signs of stress and low mood, such as being less interested in exploring new spaces, reported the Journal of Immunology.
Yet when salt was fed to mice genetically bred to not produce IL-17A, there was no increase in depression-like symptoms.
Scientists believe it’s this interaction between salty diets and the mood-changing IL-17A that might explain why eating too much may harm mental health. They now hope to carry out human studies to see if reducing salt intake also prevents this increase in protein levels and the onset of depression.
Other evidence suggests salt may be doing other, even more severe, harm to our health.
Two recent studies have found people who add it to food are more at risk of dementia, for instance.
In research published in the Journal of Affective Disorders in October, it was found to increase the chance of developing the condition by 19 per cent. A separate study, reported in the journal Brain and Behaviour last year, put it as high as 73 per cent.
Exactly how is not yet clear, but high blood pressure is one of the main contributors to vascular dementia – which affects around 180,000 people a year in the UK.
Another potential risk is hearing loss, with a study in October, by researchers in South Korea, showing that adding salt to meals heightens the risk of this by 23 per cent – possibly by disrupting the normal balance of fluid in the inner ear, which is vital for good hearing, reported the Journal of Nutrition, Health and Ageing.
But cutting back on salt intake is no easy task, says Professor Bailey: ‘I never add it to my food and yet urine tests suggest I’m still averaging about 8g a day – that shows just how difficult it is to stay within the guidelines.’
The British Heart Foundation says some of the saltiest foods are processed meats (e.g. bacon, sausages, ham), bread, pizza, sauces, baked beans and biscuits.
It recommends cutting down on ready meals or pre-made sauces and opting for low-salt versions of foods such as baked beans.
