Scientists have found that salt causes changes in the immune system in the gut – which in turn reduces blood flow to the brain.
In a new study, experiments on mice suggested that salty foods harm neurons in the brain – triggering behavioural and mental problems.
However, importantly, this damage can be reversed by returning to a normal diet, providing evidence that a change in lifestyle can help to protect against dementia.
Professor Costantino Iadecola, of Weill Cornell medical college in New York, led the study. He said: “Normal cognition function requires an adequate, well-regulated delivery of blood flow.”
The study found that mice fed a high-salt diet struggled to identify new objects in recognition tests – showing their non-spatial memory was worse.
But the effects of the salty diet were reversed after the mice were returned to a normal diet.
After four weeks brain scans showed blood flow and neuron function were healthy again.
The results suggested a high-salt diet may damage brain health in humans in addition to being bad for the heart.
This meant that a change in lifestyle or new prescription drugs could help to reverse or prevent these effects, he added.
There is no known cure for Alzheimer’s, which causes nerve-cell death and tissue loss throughout the brain leading to dementia.
During the course of the disease, the brain shrinks dramatically, affecting nearly all its functions.
British adults eat on average 8.1 grams of salt a day, compared with the recommended consumption of six grams.
Dr Doug Brown, director of research and development at the Alzheimer’s Society, said: “We often hear what is good for the heart is good for the head.
“Interestingly, this study provides a detailed insight into how what happens in the gut could also affect brain health.”
In the UK, about 850,000 people suffer from dementia. The new study is published in the journal Nature Neuroscience.