I am a clinician-scientist at Vanderbilt University Medical Center and University of Erlangen, Germany. In 1991, as a medical student in Berlin, I took a class on human physiology in extreme environments. The professor who taught the course worked with the European space program and presented data from a simulated 28-day mission in which a crew lived in a small capsule. They had collected the astronauts’ urine and other physiological markers, and noticed something puzzling in the data: Their sodium excretion went up and down in a seven day cycle.
That contradicted all I had been taught in medical school: there should be no such temporal cycle. I made a decision that I wanted to study that. 25 years later, we have learned that humans and animals store large amounts of sodium in their tissues as they age, and that this sodium storage is coupled with disease. Our work suggests that we really do not understand the effect of sodium chloride on the body, and that it is time to rethink salt.