A high-salt diet can activate a pathway in the brain and cause cognitive impairment, according to the unanticipated results of a new animal study. 

The effect is not due to reduced blood flow, as expected, but to clumps of a protein called tau, reported study lead Costantino Iadecola, M.D., of Weill Cornell Medicine, New York City.

When mice consumed the high-salt diet in the study, their brains showed evidence of tau protein clumps that coincided with reduced cognitive abilities. These tau protein aggregates interfere with the proper function of brain cells, which are known to lead to cognitive impairment and eventually dementia, wrote Iadecola and colleagues.

“This result was completely unexpected,” said Iadecola. “We knew that a high-salt diet produced dementia-like symptoms in mice, and we went in thinking the culprit would be reduced blood flow to the brain. It turned out that wasn’t the case at all.”

While the mice ate much more salt than a normal human would in a day, the findings reveal important links between diet, the brain’s blood vessels, and cognition, Iadecola said. 

“Our results highlight the importance of thinking beyond blood flow when treating disorders affecting the brain’s blood vessels,” he concluded.

The study was published in the journal Nature.