A new study from Drs. Iadecola and Faraco published in Nature offers new insights into why and how skipping the salt-shaker might protect your cognitive health. The National Institute of Health has long advised that high-salt diets are associated with high blood pressure and can raise the risk for heart disease, stroke, kidney failure, and can cause immune-related changes in the gut. This most recent study suggests that high salt intake can also impact cognitive function by causing a deficiency in a compound – nitric oxide – that is crucial for maintaining vascular health in the brain and that new findings tie to tau, one of the hallmark Alzheimer’s proteins.
A study in 2018 from the same team found that a high-salt diet contributed to cognitive deficits in mice. The mice in this study had memory impairment and were unable to complete the tasks of daily living such as building their nests. The conclusion from this earlier study was that the high-salt diet caused cells in the small intestine to release a molecule known as interleukin-17 (IL-17) which promotes inflammation as part of the body’s immune response. IL-17 enters the bloodstream where it prevented cells in the walls of the blood vessels from providing the brain with nitric oxide. Nitric oxide is crucial for relaxing and widening the blood vessels to allow blood to flow; a shortage of nitric oxide can restrict blood flow.
Following up on these initial findings, the study recently published in Nature takes the research a step farther by investigating how a change in nitric oxide production in the blood vessels affects the stability of tau proteins in neurons.
In an interview about the research, Dr. Iadecola said: “tau becomes unstable by coming off the cytoskeleton. Tau is not supposed to be free in the cell. Once tau detaches from the cytoskeleton, the protein can accumulate in the brain, causing cognitive problems.” The research provides evidence for nitric oxide playing a role in keeping tau in check.
In a crucial experiment, the researchers gave mice eating a high-salt diet an antibody to promote tau stability. Despite restricted blood flow in these mice, the researchers observed that they had normal cognition. This experiment demonstrated that the cognitive deficits in the mice on the high-salt diet were due to the effect of tau rather than restricted blood flow alone.
This research paves the way to conduct research on how salt intake affects cognition in humans – specifically Alzheimer’s patients. CureAlz is actively supporting research investigating the links among dietary salt, cardiovascular function, tau deposition, and cognitive decline.