We all know that salt is bad for health, but it remains a tempting seasoning and it is in almost everything. Still, we’d better really try to minimize our consumption: new research suggests it’s also bad for our memory and can cause dementia.
Since there is still no cure for dementia, we can only try to prevent it. One of the ways now seems to be to eat less salt. In a Japanese study cognitive decline is linked to the consumption of too much salt.
Recommended daily amount
It has long been known that eating too much salt leads to high blood pressure and can therefore cause cardiovascular disease. That is why the World Health Organization (WHO) recommends limiting salt intake to a maximum of 5 grams per day. To give you an idea: there is about 1 gram of salt in three slices of bread. A jar of pasta sauce usually contains at least 1 gram per 100 grams of sauce. The Dutch therefore on average go well over the recommended daily amount of salt. Adult men eat an average of almost 10 grams of salt per day, women 7.5 grams. Incidentally, the Dutch guideline is somewhat more flexible. We are allowed 6 grams of salt per day instead of the 5 grams recommended by the WHO.
Proteins and hormones
Back to the Japanese research. They looked at the role of angiotensin II – a hormone important for the regulation of blood pressure and fluid balance – and its receptor AT1. They also investigated the role of the protein molecule prostaglandin E2 and its receptor EP1, which are also known to be involved in high blood pressure and neurotoxicity. But the question now is to what extent these mechanisms are involved in high blood pressure and cognitive decline caused by excessive salt intake.
The scientists have found an answer to that. They found that salt-induced high blood pressure, mediated by the interaction of Ang II-AT1 and PGE2-EP1, does indeed cause emotional and cognitive problems.
Researcher Hisayoshi Kubota of the Fujita Health University responds: “Excessive salt intake is considered a risk factor for high blood pressure, cognitive decline and dementia. But studies that have focused on the interaction between the peripheral and central nervous systems have not sufficiently looked at this link.”
The Japanese did. According to the published data, the addition of excessive phosphates to the protein tau is mainly responsible for these emotional and cognitive consequences. That is a very interesting fact, because tau is an important protein in the development of Alzheimer’s.
Salt overdose for lab mice
How did the researchers find out? They gave lab mice a saline solution of 2 percent salt in drinking water for twelve weeks and monitored their blood pressure. “The effects of salt intake on emotional and cognitive functions and tau phosphorylation have also been studied in two key areas of the mouse brain, the prefrontal cortex and the hippocampus,” explains researcher Professor Akihiro Mouri. They then looked at the role of Ang II-AT1 and PGE2-EP1 in salt-induced hypertension and neuronal and emotional decline.
The results were impressive: the brains of the lab mice had undergone several biochemical changes. At the molecular level, in addition to an addition of phosphates to tau, the researchers also observed a decrease in phosphate groups linked to a key enzyme called CaMKII, a protein involved in brain signaling. There were also changes in the level of PSD95, a protein that plays a vital role in the organization and function of brain synapses. Surprisingly (and fortunately) all of these changes could be reversed by administering an antihypertensive drug.
New treatment method
What should we do with all these complicated findings? They may make the angiotensin II-AT1 and prostaglandin E2-EP1 systems potentially new targets in the treatment of high blood pressure-induced dementia. And how can we influence these systems? Right, by eating less salt. “This study is especially of great social and economic importance, because the costs of the treatment of dementia are increasing every year,” it concludes. That is why it is important to develop preventives that protect against dementia.
The figures show how important research into dementia is. Due to the aging of the population, the number of Dutch people suffering from the condition has increased sixfold: from 50,000 in 1950 to 290,000 now, writes Alzheimer Nederland. In 2040 that number will probably increase to 500,000 people and in 2050 about 620,000 Dutch people will probably have dementia. As many as one in three women will develop dementia at some point, compared to one in seven for men.
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