Study Finds a High-Salt Diet May Cause Dementia
Scientists conducting a study at Weill Cornell Medicine found a high-salt diet decreased resting blood flow to the brain and produced dementia in mice. The discovery was the first to show a link between excess salt consumption and neurovascular and cognitive impairments. It has implications for the 90 percent of Americans whose diet contains more than the recommended limit of 2,300 mg of salt per day.
“We discovered that mice fed a high-salt diet developed dementia even when blood pressure did not rise,” said senior author Dr. Costantino Iadecola, director of the Feil Family Brain and Mind Research Institute (BMRI) 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.”
High-Salt Diet Reduced Blood Flow to Memory and Learning Brain Regions
In the study published in Nature Neuroscience, mice were fed a diet containing 4 to 8 percent salt, which is an 8- to 16-fold increase in the salt contained in a normal mouse diet. The 8-percent salt diet is equivalent to what people would ingest who are at the high end of salt intake. At the end of eight weeks, magnetic resonance imaging revealed marked decreases in resting blood flow in two regions of the brain involved in memory and learning: 25 percent in the hippocampus and 28 percent in the cortex.
Iadecola and his colleagues also noted a reduced ability of the endothelium, a term for the cells lining the blood vessels, to produce nitric oxide, a gas that relaxes blood vessels and boosts blood flow. To determine if these harmful effects of a high-salt intake could be reversed, the researchers switched some of the mice back to a regular diet for four weeks. They found normal endothelial function and cerebral blood flow were restored.
Only the mice that ate the high-salt diet developed dementia, performing worse on a maze test, an object recognition test and nest building, which is a typical activity of daily living for mice.
Underlying Mechanism of the High-Salt Diet Link to Dementia Discovered
In the next stage of the study, the scientists conducted experiments to determine the underlying mechanisms that tie a high-salt diet to dementia. They observed higher activity of a variety of white blood cells that increase the manufacture of a protein called interleukin 17 (IL-17), which causes the endothelial cells to make less nitric oxide.
The findings give the public another reason to avoid dietary elements that contain large amounts of salt, including processed food, cold cuts, cured meats, soups, pizzas, burgers, fries and snacks such as chips, crackers and pretzels. While a high-salt diet causes health problems, severely restricting salt in the diet is also not beneficial, as a certain amount is essential for good health. Cooking wholesome, nutritious meals at home permits control of the amount of salt ingested.
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