The ‘poison’ we all eat

Heart failure, stroke, kidney problems, osteoporosis. oedema – all are conditions linked to high salt intake. According to a new study, you should now add an increased risk of dementia to that list.

Researchers from Weill Cornell Medicine in New York have found that a high salt diet can lead to a drop in nitric oxide, which is vital for brain health.

When nitric oxide levels are too low, chemical changes to the protein tau occur in the brain, contributing to dementia, the researchers reported in an article published in Nature this week.

In the study, the investigators sought to understand the series of events that occur between salt consumption and poor cognition in mice and concluded that lowering salt intake and maintaining healthy blood vessels in the brain may “stave off” dementia.

Accumulation of tau deposits has been implicated in the development of Alzheimer’s disease in humans.

“Our study proposes a new mechanism by which salt mediates cognitive impairment and also provides further evidence of a link between dietary habits and cognitive function,” said lead study author Dr Giuseppe Faraco, an assistant professor of research in neuroscience in the Feil Family Brain and Mind Research Institute at Weill Cornell Medicine.

The new study builds on research published last year in Nature Neuroscience by Dr Faraco and senior author Dr Costantino Iadecola.

The 2018 study found that a high-salt diet caused dementia in mice. The rodents became unable to complete daily living tasks such as building their nests and had problems passing memory tests. The research team determined that the high-salt diet was causing cells in the small intestine to release the molecule interleukin-17 (IL-17), which promotes inflammation as part of the body’s immune response.

IL-17 then entered the bloodstream and prevented the cells in the walls of blood vessels feeding the brain from producing nitric oxide. This compound works by relaxing and widening the blood vessels, allowing blood to flow. Conversely, a shortage of nitric oxide can restrict blood flow.

In their new Nature study, the investigators found that decreased nitric oxide production in blood vessels affected the stability of tau proteins in neurons. Tau provides structure for the scaffolding of neurons. This scaffolding helps to transport materials and nutrients across neurons to support their function and health.

The current mouse study was a reminder for people to regulate salt consumption, Dr Iadecola said. “And the stuff that is bad for us doesn’t come from a salt shaker, it comes from processed food and restaurant food. We’ve got to keep salt in check. It can alter the blood vessels of the brain and do so in a vicious way.”

The Heart Foundation says the average Australian should aim to consume fewer than five grams of salt a day, which is less than one teaspoon. It says most of us are exceeding this with the average Australian consuming about nine grams daily.

Are you mindful of your salt consumption? Did you know the recommended daily limits?

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Written by Janelle Ward

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