Does Salt Raise the Risk of Dementia?

I'm sure you've received the message loud and clear by now that too much salt is bad for you. Medical authorities tell us it pushes up blood pressure, thereby contributing to heart attacks and strokes. I’ve been hearing about this for years. Already when I was a child, back in the 1960s, I remember the old folks being told by their doctors they couldn’t eat salt. It turns out this is almost entirely myth. A small number of high blood pressure cases, maybe one out of ten, are the result of salt sensitivity. But now comes a new salt scare – we’re told it contributes to dementia. And not merely in one way, but two: too much salt OR too little poses a danger. Is there anything to this new attack on salt? Researchers in a new study did find a link between high salt intake and dementia, but it was different from what they expected. They found that the salt-dementia link had nothing whatever to do with high blood pressure. It came from a newly discovered mechanism. More surprising, they found that people on low salt diets are not out of the woods either, because too little salt also increases the risk of dementia.

Reduces Blood Flow by a Quarter

Scientists from Weill Cornell Medical College in New York fed mice a diet containing either 8 or 16 times their normal intake. The upper figure equated to the top end of human consumption. At the end of two months, brain scans showed 25% and 28% reductions in resting blood flow in the hippocampus and cortex respectively. Both areas are key for learning and memory. The endothelial cells which line the blood vessels were also found to produce less nitric oxide (NO). This chemical relaxes blood vessels and increases blood flow (a fact that has made NO-boosting supplements extremely popular). The NO-dampening effect of salt was reversed when the mice returned to eating a normal amount. After three months, the high salt mice developed dementia and performed worse on three tests of mental functioning. This happened even in mice whose blood pressure wasn't raised. The scientists were surprised by this finding, because the negative effects of salt on cognition have always been put down to hypertension. In further experiments they found that a high salt intake prompted an immune response in the small intestine to boost circulating levels of an inflammatory protein called interleukin-17. It was this that caused the reduction in nitric oxide, which in turn lowered blood flow and brought on the negative consequences for cognitive ability. In the opinion of the study’s authors, "The findings reveal a new gut-brain axis linking dietary habits to cognitive impairment through a gut-initiated adaptive immune response compromising brain function via circulating IL-17." Now a key point here is that these results must be seen in humans before they’re confirmed. And my research team found at least one study that suggests they will be. . .

Low Sodium Reduces Cognition by 30%

The study suggests that even those resistant to salt's negative cardiovascular effects (which is most of us) can't be complacent because salt might still be damaging the brain. But going to the other extreme by keeping salt intake to a minimum might not be such a good idea either. A team of researchers from Stanford, the University of California San Diego, and the University of Colorado examined data from 5,435 symptom-free elderly men (all were over the age of 65). The participants were monitored for 4½ years. It was found that a very small number -- 100 -- had low blood levels of sodium, a condition called hyponatremia. Compared to those with normal levels, the men with hyponatremia had a 30% greater likelihood of cognitive impairment at the start of the study, and were 37% more likely to suffer cognitive decline over time. Those with high levels of sodium in the blood also experienced a greater risk of cognitive decline. Lead researcher Kristen Nowak, MD, said, “To our knowledge, our findings are the first to demonstrate an independent association between lower serum sodium and cognitive decline in generally healthy community-dwelling older men.” It seems "everything in moderation" is a phrase which we should all take to heart when it comes to the intake of salt. Do take note that low sodium is an extremely rare condition among humans, American division. I don’t think most of us have to worry about finding ourselves on that end of the salt-intake spectrum.

Nutrition

Does Salt Raise the Risk of Dementia?

Reduces Blood Flow by a Quarter

Low Sodium Reduces Cognition by 30%

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