While a considerable number of studies have linked high salt intake to blood pressure and heart disease risks, researchers said less attention had been paid to potential cognitive effects.
In this study, mice were fed a high-salt diet, comparable to the excessive proportion of salt found in some human diets.
Writing in the journal Nature Neuroscience, researchers stated: "We investigated the mechanisms of the harmful effects of dietary salt on the brain. It has long been known that a high-salt diet leads to alterations in endothelial function of cerebral and systemic vessels resulting from a reduction in endothelial nitric oxide (NO).
"However, most studies focused on salt-induced hypertension, and it has remained unclear how long-term dietary salt intake altered cerebrovascular regulation and brain function independently of blood pressure."
Within a few weeks, the high-saltdiet led to endothelial dysfunction, a reduction in cerebral blood flow, and cognitive impairments in several behavioural tests, but no changes in blood pressure.
The diet also increased the numbers of TH17 white blood cells in the gut and increased the levels of a pro-inflammatory molecule these cells release, called IL-17.
The authors then found that it was this increase in IL-17 in the bloodstream that caused the high-salt diet's negative effects on cerebrovascular function and behaviour.
"We have demonstrated that a high-salt diet induces a TH17 response in the gut that leads to increases in circulating IL-17, which, in turn, act on cerebral endothelial cells to suppress endothelial NO production, leading to reductions in cerebral perfusion and cognitive dysfunction," they wrote.
Although these results were obtained in mice, the researchers also showed that IL-17 similarly affects human cerebral endothelial cells, suggesting that a high-salt diet might also negatively impact brain health in humans, regardless of its effect on blood pressure.
However, the effects of the high-salt diet were found to be reversible after the mice were returned to a normal diet, or by pharmacological intervention, suggesting that a change in lifestyle or new prescription drugs could help reverse or prevent these effects.
The researchers concluded: "While these findings highlight the key role of cerebral endothelial function in brain health, they also unveil a previously undescribed gut–brain axis, whereby dietary habits compromise the brain microvasculature, leading to altered brain function and cognitive impairment."
Source: Nature Neuroscience
"Dietary salt promotes neurovascular and cognitive dysfunction through a gut-initiated TH17 response"
Authors: Giuseppe Faraco, et al.