Salt water damages people

Salt can damage the brain

A diet that is too salty is an important risk factor for high blood pressure and cardiovascular diseases. But too much salt can apparently also damage our brain, as a study with mice has now revealed. Accordingly, a high-salt diet causes the release of special immune messenger substances in the intestine. These, in turn, impair the function of the veins in the brain and lead to measurable cognitive losses - regardless of blood pressure or known inflammatory reactions.

Our body needs salt: Without the sodium in table salt, the nerves cannot transmit signals and the muscles also do not work properly. Salt also helps the body regulate our water balance. However, in recent years there has been increasing evidence that too much salt can be harmful to health in the long term. In certain people, this increases blood pressure and can promote vascular inflammation and cardiovascular diseases. At the same time, an increased salt intake seems to stress the heart regardless of blood pressure and to lead to an increased risk of heart failure, as researchers only found out last year. Based on these data, the World Health Organization recommends not consuming more than six grams of salt per day.

Memory problems after eight weeks

It has long been suspected that a salty diet could also damage the brain. Giuseppe Faraco from Weill Cornell Medicine in New York and his colleagues have now investigated whether this is the case and what mechanisms are behind it. For their study, they first gave various groups of mice a food that contained four or eight percent table salt. "This makes this diet comparable to what people eat on a very salty diet," the researchers explain. After eight weeks of this feeding, the researchers examined how the blood flow to the brain had changed as a result. The result: The blood flow in the animals fed with a high salt content had decreased by 28 percent in the cortex and by 25 percent in the hippocampus, which is important for memory.

To find out how this affected the cognitive performance of the mice, the researchers carried out two different memory tests. In the first, they observed whether the animals were able to distinguish already known objects from completely new ones - the latter would then have to be eyed and sniffed for longer. In the second, the mice were supposed to remember where the exit was in a maze. It was found: In both tests, the animals fed with a high salt content fared significantly worse than the normally fed control mice. This was true for both younger and older mice, as the scientists report. However: These cognitive losses proved to be reversible: If the mice were given the normal, low-salt diet for a few weeks, their memory performance also improved again.

Effect independent of blood pressure and inflammation

The question now arose as to what caused the salt to have these effects. The previously known consequences of a high-salt diet can often be traced back to chronic inflammation of the vessels and vessel walls. “In this case, however, we did not find any evidence of increased activity of inflammatory enzymes,” the researchers report. The inflammation genes in the cerebral vessels were also not read more intensely. "That speaks against the fact that the cognitive losses and disorders of the cerebral blood flow are due to an inflammatory reaction," said Faraco and his colleagues.

Instead, on closer analysis, the researchers discovered a different connection: When the mice were given a high-salt diet, the number of certain immune cells in their intestines increased and with them the amount of the messenger substance interleukin-17 (IL-17) released. This messenger substance in turn circulates in the blood and thus also reaches the brain. There it interferes with the supply of the blood vessels with nitric oxide (NO), a compound that ensures the expansion of the veins and thus the good blood flow to the brain. Experiments showed that if the scientists inhibited the production of interleukin-17 in the mice, the cognitive and neurovascular consequences of the high-salt diet did not occur in them.

"Our observations thus reveal a previously unknown connection between the intestine and the brain," state Faraco and his colleagues. "According to this, high-salt food can damage the brain vessels and thereby impair brain function and cognitive performance - regardless of blood pressure." People. Because in supplementary experiments, human cerebral vascular cells also reacted to interleukin-17.

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© Wissenschaft.de - Nadja Podbregar
January 15, 2018