A high-salt diet may not only be bad for one's blood pressure, but also for the immune system, according to a study.
Researchers from the University Hospital Bonn in Germany found that mice fed a high-salt diet suffered from much more severe bacterial infections.
Human volunteers who consumed an additional six grams of salt per day also showed pronounced immune deficiencies, according to the study published in the journal Science Translational Medicine.
This amount corresponds to the salt content of two fast food meals, the researchers said.
Five grams a day is the maximum amount of salt that adults should consume according to the recommendations of the World Health Organization (WHO).
It corresponds approximately to one level teaspoon, the researchers said.
Sodium chloride, which is the chemical name of salt, raises blood pressure and thereby increases the risk of heart attack or stroke, they said.
"We have now been able to prove for the first time that excessive salt intake also significantly weakens an important arm of the immune system," said Christian Kurts from the University of Bonn.
The researchers said that the finding is unexpected, as some studies point in the opposite direction.
For example, infections with certain skin parasites in laboratory animals heal significantly faster if these consume a high-salt diet, they said.
The macrophages, which are immune cells that attack, eat and digest parasites, are particularly active in the presence of salt.
Several physicians concluded from this observation that sodium chloride has a generally immune-enhancing effect, the researchers said.
"We examined volunteers who consumed six grams of salt in addition to their daily intake," said Kurts.
"This is roughly the amount contained in two fast food meals, i.e. two burgers and two portions of French fries," he said.
After one week, the scientists took blood from their subjects and examined the granulocytes, the most common type of immune cell in the blood.
They found that the immune cells coped much worse with bacteria after the test subjects had started to eat a high-salt diet.