According to new research, cutting down on salt could help prevent Alzheimer’s disease. The seasoning fuels the development of ‘tau tangles’ clumps of protein that collect in the brain and cause the memory-robbing illness. People with salt-rich diets are known to be at higher risk of dementia, however, the reason remained a mystery. Now scientists say they’ve discovered how gorging on processed foods and ready meals could lead to dementia. Corresponding author, Professor Costantino Iadecola, one of the world’s leading neurologists, said: “The results identify a previously unknown pathway linking dietary habits and cognitive function.” When mice were fed food laced with salt it triggered a “cascade” of chemical reactions that culminated in increased levels of tau
They became less competent at recognising new objects and struggled with a maze test.
Professor Iadecola said: “Starting after 12 weeks of high salt diet, mice exhibited difficulties in recognising novel objects and developed a deficit in spatial memory for the maze.”
Lack of spatial awareness is one of the major symptoms in the early stages of dementia.
Too much salt reduced production of nitric oxide (NO) which helps keep grey matter healthy by boosting blood flow in the brain, said the US team.
This activated an enzyme called CDK5 that is critical for making tau. When the gas was restored in the lab rodents cognitive impairment was reversed.
The researchers did this by feeding them Arginine in their water – an amino acid found in all forms of life.
Levels of NO are known to be low in the brains of people who have Alzheimer’s disease.
The findings published in Nature could lead to treating patients with nitric oxide drugs. Prof Iadecola, of Weill Cornell Medicine, New York, said: “Here we report dietary salt induces hyper-production of tau followed by cognitive dysfunction in mice.
“These effects are prevented by restoring nitric oxide.
The deficiency results in enzyme activation, which, in turn, leads to tau. These findings identify a causal link between dietary salt and tau pathology.”
Avoiding excessive salt intake and maintaining vascular health may help stave off dementia in the elderly, he said.
The groundbreaking study is the first to identify a causal link. Prof Iadecola pointed out the mice were given eight to 16 times their normal amount of salt.
This is more than the highest reported levels of consumption in humans – 3 to 5 times the recommended six teaspoons, or four to five grams, per day.
But the experiments uncovered how an extremely high-salt diet can lead to the accumulation of tau.
Prof Iadecola said: “Vascular risk factors, including excessive salt consumption, have long been associated with cerebrovascular diseases and cognitive impairment.
“A diet rich in salt is an independent risk factor for stroke and dementia and has been linked to the cerebral small vessel disease that underlies vascular cognitive impairment, a condition that is associated with reduced cerebral blood flow.
“Our data provide a previously unrecognised link between dietary habits, vascular dysfunction and tau pathology.
Such relationships may play a role in the frequent coexistence of vascular and neuro-degenerative pathologies in conditions that cause dementia, such as Alzheimer’s disease and fronto-temporal dementia.
Dementia effects an estimated 850,000 people in the UK – a figure set to rise to two million by 2050 because of the ageing population.
With no cure in sight there is increasing focus on lifestyle changes that can protect against the disease – such as eating healthier foods and doing more exercise.
The Alzheimer’s Society says a good diet is an important factor in reducing the risk of dementia.
It advises people to look out for hidden salt in foods – and consume plenty of fruit, vegetables and oily fish and less saturated fat.
Prof Iadecola said further research is needed to explore whether the results may be translated to humans.
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