Too much salt may lead to cognitive disorders, high blood pressure

Researchers estimate the majority of people around the world consume between 9 to 12 grams of added salt each day. This is much higher than the daily recommended maximum intake of sodium.

A high-salt diet is a known risk factor for high blood pressure. Previous research has also linked an increased table salt intake to cognitive decline and a higher risk for dementia.

Additionally, people with high blood pressure are at an increased risk of developing dementia.

Now, researchers from Fujita Health University have taken our knowledge of the link between hypertension and dementia even further by identifying the specific body systems involved in high salt-caused hypertension and cognitive impairment via a mouse model.

Additionally, researchers found the addition of excessive phosphates to the tau protein is primarily responsible for emotional and cognitive issues.

Tau is a key protein associated with the development of a type of dementia called Alzheimer's disease.

This study was recently published in the British Journal of Pharmacology.

According to researchers, although high salt consumption is considered a risk factor for high blood pressure, cognitive dysfunction, and dementia, studies focusing on the interaction between the peripheral and central nervous systems have not sufficiently investigated this association.

In this study, scientists used a mouse model to investigate this association further. The researchers gave the mice high-salt drinking water for 12 weeks and monitored their blood pressure.

The research team also monitored the effects of the high salt intake on their emotional and cognitive function and tau phosphorylation in the brain's prefrontal cortex and hippocampus areas.

The researchers studied the roles of two systems — the hormone angiotensin II (Ang II) and its receptor AT1, and the lipid molecule prostaglandin E2 (PGE2) and its EP1 receptor — play in the development of high salt-induced hypertension and neuronal impairment.

Ang II-AT1 plays an important role in regulating the body's blood pressure and fluids. PGE2-EP1 also has a direct impact on blood pressure.

After the study, the research team observed several biochemical alterations in the brains of the mice. In addition to the excessive tau protein phosphates, scientists also found a decrease in the phosphate groups linked to the CaMKI enzyme. The CaMKI enzyme is involved in brain signaling.

Additionally, researchers found changes in the levels of the protein PSD95 in the brains of the mice, which plays an important role in how the connections between brain cells — or brain synapses — function.

The researchers reported that these biochemical changes were reversed when the mice were treated with the high blood pressure medication losartan or when the EP1 gene was knocked out.

Scientists believe these findings may pave the way for new therapeutics for hypertension-induced dementia by targeting the AGII-AT1 and E2-EP1 systems.

Dr. Sandra Narayanan, a board certified vascular neurologist and neuro interventional surgeon at Pacific Stroke & Neurovascular Center at Pacific Neuroscience Institute in Santa Monica, California, told Medical News Today that multiple aspects of this research were interesting to her.

"In this animal model, it was interesting to note how adverse biochemical changes from a high sodium intake (and) hyperphosphorylation of the protein tau that is associated with cognitive impairment and neuronal loss and Alzheimer's and other dementias was associated with shortened length of brain cells, or dendritic length, particularly in brain regions that are involved in memory, such as the hippocampi," she explained.

"And also how there's a very complex interaction between the different components of the hormones that are associated with activation of vascular disorders and development of hypertension," she added.

Dr. Narayanan also commented on how in a very short period of six to 12 weeks, the adverse changes that can occur from a high sodium diet were evident in the mouse model.

She said once the adverse impacts of a high sodium diet are known, therapeutic interventions can be designed to potentially reverse the changes.

"One doesn't think of dementia as being reversible with blood pressure medications, but if there's biochemical evidence that the early steps of these diseases can be slowed down or reversed with aggressive blood pressure lowering by some of these biochemical mechanisms and by (the) pharmacological mechanisms underlined in the paper, that's quite exciting," Dr. Narayanan added.

Salt is a mineral made mostly of sodium chloride.

It is also an essential nutrient for the body and its organs. Sodium in the body aids with:

The body only requires a very small amount of salt. Currently, the recommended daily intake of sodium for an adult is less than 2,300 milligrams or 2.3 grams per day.

A salt intake of 5% or less of that daily recommendation is considered a low-salt diet. And consuming 20% or more of the daily recommended amount is regarded as a high-salt diet.

When most people think of "added salt," they think of the table salt they may shake onto their food. However, most added salt comes from processed and prepared foods.

In addition to high blood pressure, a high-salt diet has also been linked to an increased risk for:

For those who may want to decrease their salt intake to help lower their risks for both high blood pressure and dementia, Dr. Narayanan said it's all about minimizing eating out or eating processed foods, and eating smaller portions.

"You can ask for your dish to be made with less salt, but recognize that there's not as much control when you are not preparing your own foods, or you’re not seeing the ingredients, condiments, and flavorings that are going into it," she added.

Dr. Narayanan advised using spices, fresh and dried herbs, and fresh vegetables to add flavor and minimize using salty condiments such as soy sauce, mustard, pickles, ketchup, olives, and cheeses when cooking at home.

For additional low-salt lifestyle and cooking tips, Dr. Narayanan suggested visiting the American Heart Association's website.