Proof salt doesn’t make you thirsty
THE idea that eating too much salt makes you thirsty may be nothing more than an old wives’ tale, scientists believe.
In a study carried out during a simulated mission to Mars, researchers found that “astronauts” who ate more salt retained more water, were not as thirsty and were hungrier.
The scientists from the German Aerospace Centre examined the connection between salt intake and drinking using a mock flight to Mars.
They simulated a long space voyage using an environment in which every aspect of a person’s nutrition, water consumption and salt intake could be controlled and measured.
Researchers used two groups of 10 male volunteers sealed into a mock spaceship for two simulated flights to Mars. The first group was examined for 105 days, the second over 205 days.
Each group had identical diets except that over periods lasting several weeks, they were given three different levels of salt in their food. As expected, the results confirmed that eating more salt led to a higher salt content in urine and found a correlation between amounts of salt and overall quantity of urine.
But the increase was not due to more drinking – in fact, a salty diet caused the subjects to drink less, triggering a mechanism to conserve water in the kidneys.
Study co-leader Professor that would otherwise be carried away into the urine.”
Before the study, scientists had believed that the charged sodium and chloride ions in salt grabbed on to water molecules and dragged them into the urine.
But the new results showed something different, that salt stayed in the urine, while water moved back into the kidney and body. And thirst was not increased with increases of salt.
Tests in mice also showed salt did not increase their thirst, but it did make them hungrier – which was also observed in the humans.
The findings, published in the Journal of Clinical Investigation, shed new light on the way the body achieves water homeostasis – maintaining the proper amount.
Professor Jens Titze said: “We now have to see this process as a concerted activity of the liver, muscle and kidney.
“While we didn’t directly address blood pressure and other aspects of the cardiovascular system, it’s also clear that their functions are tightly connected to water homeostasis and energy metabolism.”