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Does a High Salt Diet Harm the Brain?

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Does a High Salt Diet Harm the Brain? about undefined
Last year scientists thought they'd discovered why excessive salt intake causes memory loss. It's because salt restricts blood flow to the brain. But it turned out they were wrong. True, it does restrict blood flow, they were right about that, but this isn't the main reason behind the damaging effects of massive salt intake. So they dug deeper and carried out more research. This resulted in a completely new finding -- a finding that should cause concern to those who consume really excessive amounts of salt. . . In a 2018 study, world leading neurologist Costantino Iadecola and his colleague Giuseppe Faraco at Weill Cornell Medicine, New York, found that a diet high in salt causes dementia in mice. This occurs because salt provokes the release of an inflammatory molecule called interleukin-17 from the small intestine. When this molecule enters the bloodstream, the production of nitric oxide is held back. Nitric oxide relaxes and dilates blood vessels, allowing blood to flow to the brain. The scientists assumed dementia in the mice was caused by this restriction of blood. But they came to realize that while this is certainly harmful in itself, it wasn't severe enough to cause the brain damage they observed. The problem had to come from something else. So they designed a new mouse study which was published in Nature in October. . .

Tangles and Tau

This time they looked closely at the events that take place when nitric oxide is restricted. They discovered that a nitric oxide deficit puts the brake on a series of enzyme reactions that lead to tau proteins in brain cells becoming destabilized and breaking away from the cytoskeleton (“cell skeleton” or scaffolding) of neurons. Tau provides structure for the cytoskeleton and is not supposed to be free in the cell. When it becomes untethered, accumulation in the brain follows. This causes harmful changes that lead to cognitive decline and memory loss. Commenting on their findings, Dr. Faraco said, "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." His colleague Dr. Iadecola added, "[T]he stuff that is bad for us doesn't come from a saltshaker, 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 message is clear, but it's important to get things in perspective.

No Need to Panic

For the study the mice were given more than eight times their normal daily salt intake. This would be the equivalent of humans ingesting 7.5 grams of sodium - more than double the average American consumption of 3.4 grams of sodium a day – which itself is quite high. An individual would have to be living on processed foods and restaurant meals to get anywhere near the equivalent of what the mice were forced to endure. Dr. Evangeline Mantzioris, program director of nutrition and food sciences at the University of South Australia, praised the research, but cautioned the salt intake of the mice was incredibly high and "we cannot with certainty say the same effect would happen in humans." Her fellow Australian, Professor John Funder, a leading neuroscientist at the University of Melbourne, went much further, saying, "Any extrapolation from mice on a salt intake of eight percent to the human grossly irresponsible in terms of science." The study is important, being the first to demonstrate a link between what the researchers called "excessive salt intake" and tau pathology, but it does no more than point to the possible impact of salt in humans.

My Take

So, as often happens, more study is needed. I’m most concerned about salt’s potential impact on nitric oxide to the brain. I’d be interested to learn more, including some studies involving humans. But a mouse study with a mega-intake of salt doesn’t tell me much. I’ve always been a skeptic of the medical profession’s scary warnings about salt. For years, people with high blood pressure were told to give up salt. This was not an effective approach. I looked into this years ago, and only about ten percent of hypertension patients had a salt problem. For the other nine out of ten, giving up salt was useless (and very hard to do.) There are also one or two famous anticancer diets that demand a no-salt regimen, but this was not backed by studies. The diets came from respectable alternative doctors, but after fifteen years of writing about alternative cancer treatments, I’ve learned that opinions and theories far outnumber provable facts. Now we have a weakly supported claim that salt – really massive amounts of it – might contribute to dementia. At this point, I’m not going to change my habits, which are pretty moderate anyway. And as for salt-heavy processed, packaged and fast foods – it’s always good advice not to eat them. I don’t.

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