How much sodium should people get every day? The answer has gone up and down over the past few years.
Studies have shown that overindulging in salt can lead to higher risk of developing diabetes, heart failure, and even multiple sclerosis. But other studies have found that low-salt diets may not help everyone, and might not even contribute to lower blood pressure.
In the study, researchers fed mice a diet containing either 4% or 8% salt—that's 8-16 times more then a regular mouse diet, but the higher amount is equivalent to what a human would consume at the upper limits of recommended salt consumption. (The recommended daily amount is 2,300mg, but the majority of American adults take in about 3,400mg a day, says the CDC.)
The scientists found that after eight weeks the mice showed large reductions in blood flow into the brain—28% less to the cortex (at which higher brain functions happen), and 25% less to the hippocampus (at which most memory is located). The researchers also discovered that cells lining blood vessels lowered their production of nitric oxide, which is needed to keep the vessels relaxed and open for optimal blood flow. The mice also developed dementia and did considerably worse on cognitive tests.
"We discovered that mice fed a high-salt diet developed dementia even when blood pressure did not rise," said senior author Costantino Iadecola, M.D., director of the Feil Family Brain and Mind Research Institute and the Anne Parrish Titzell Professor of Neurology at Weill Cornell Medicine. "This was surprising since, in humans, the deleterious effects of salt on cognition were attributed to hypertension."