Excess Salt May Hurt Your Brain, Too

Jan. 29, 2018 — Salt has for years been cited as a cause of high blood pressure. Now new research suggests high-salt diets may harm your brain, too.

The latest study to show a link between a high-salt diet and memory and thinking problems was done in mice. But earlier research on humans suggests a link between high-salt diets and brain health as well.

In the newest study, researchers fed mice either 8 or 16 times the normal amount of salt in their diet. Within 8 to 12 weeks, the mice showed signs of memory and thinking problems. They had trouble telling new and familiar objects apart. It got harder for them to get through mazes. And they couldn’t build a nest as well. These behaviors are all central to a mouse’s interaction with the world.

Potential Game-changer

The study could change the conversation about diet with her patients, says Pinky Agarwal, MD, a neurologist who specializes in movement disorders like Parkinson’s disease at EvergreenHealth in Kirkland, WA, and a fellow of the American Academy of Neurology.

When doctors think about salt and patient health, they focus mostly on high blood pressure, or hypertension, cardiovascular disease, and stroke, she says.

““If a patient does not have hypertension, we don’t talk about salt at all,” says Agarwal, who was not involved in the study. “This study provides a good reason for us to ask everyone about salt intake.”

What Salt Does

The effects that Iadecola found follow an indirect path. When the mice ate their doctored food, the excess salt triggered a response in their small intestine. It started to produce large amounts of Th17, a type of white blood cell involved with the immune system. This led to a rise in levels of another component of the immune system, a protein called IL-17.

High Salt = Higher Rates of Disease

Hafler’s own research supports the significance of this new study. In 2013, he and his colleagues published the first study demonstrating that excess salt boosts levels of Th17 and influences the development of multiple sclerosis. That discovery may help explain the rise in MS and other autoimmune diseases, like psoriasis, inflammatory bowel disease, and rheumatoid arthritis.

“The effect of salt is just absolutely dramatic,” says Hafler.

More Than Just Hypertension

Agarwal says there’s probably a need for tests and questionnaires that will let doctors find out how much salt their patients eat. Most dietary salt, after all, does not come from the saltshaker on your kitchen table. It’s in processed foods and restaurant meals, and that makes it hard to calculate.

Effects May Be Reversible

If you love salty food, there could be some good news. Once the mice returned to their normal diet, their brain function returned to normal as well. That suggests that problems caused by eating too much salt may be reversed once you cut back. And, of course, these problems may be prevented by avoiding a high-salt diet in the first place, says Agarwal: “It’s something that can be controlled.”

The mice in the study remained on their high-salt diet for only 3 months. Is there a point at which the brain will begin to suffer permanent damage?

“We don’t know what will happen if you do this for 10 years,” says Iadecola. “My suggestion is that because the blood flow is reduced in the brain and because then the blood vessels in the brain don’t work correctly, something major is going to happen if you keep this up. … Watching salt intake may be an important step to preventing dementia.”

Sources

Pinky Agarwal, MD, neurologist, EvergreenHealth, Kirkland, WA.

Costantino Iadecola, MD, professor of neurology and neuroscience, Weill Cornell Medical College, New York.

David Hafler, MD, professor and chairman of neurology and professor of immunobiology, Yale School of Medicine, New Haven, CT.

Afsar, B. High Blood Pressure & Cardiovascular Prevention, March 26, 2013.

American Heart Association: “How Much Sodium Should I Eat Per Day?”

Fiocco, A. Neurobiology of Aging, August 19, 2011.

Reuters: “Too much salt may trigger autoimmune diseases: studies.”

Rush, T. The Journal of Nutrition, Health and Aging, March 2017.

News release, Yale University, March 6, 2013.

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