A high-salt diet in mice can lead to changes in the immune system in the gut that can then cause deficits in cognitive function, reports a study published in Nature Neuroscience this week.

In humans, a salt-rich diet is known to cause high blood pressure and increase the risk of developing cardiovascular diseases. At a cellular level, excessive salt consumption leads to the dysfunction of endothelial cells, the cells that line blood vessels and modulate vascular tone, but the long-term impact of such dysfunction on various organs is unknown.

Costantino Iadecola and colleagues fed mice a high-salt diet, comparable to the excessive proportion of salt found in some human diets. Within a few weeks, the salty diet led to endothelial dysfunction, a reduction in cerebral blood flow, and cognitive impairments in several behavioral tests, but no changes in blood pressure. The salty 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 salty diet’s negative effects on cerebrovascular function and behavior.

Although these results were obtained in mice, the study also shows 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. Importantly, the effects of the salty diet were 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.