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Sodium rhythms explored via space flight simulation
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In a study examining the salt intake and balance of Russian cosmonauts, researchers discovered rhythmic sodium excretory and retention patterns independent of blood pressure or water. The findings were published in the journal Cell Metabolism.
“We understand now that there are 7-day and monthly sodium clocks that are ticking, so a 1-day snapshot shouldn’t be used to determine salt intake,” researcher and clinical pharmacologist Jens Titze, MD, of Vanderbilt University School of Medicine, said in a press release.
In two simulations (Mars 105 and Mars 520), the researchers fixed the salt intake of the cosmonauts to 12 g, 9 g and 6 g per day for months, besides tests for predicted constancy in urinary excretion and total-body sodium content.
“It was the participants’ stamina to precisely adhere to the daily menu plans and to accurately collect their urine for months that allowed scientific discovery,” Titze said in the press release.
At constant salt intake, daily sodium excretion showed aldosterone-dependent, weekly (circaseptan) rhythms, leading to periodic sodium storage, according to data.
The changes in total body sodium (±200 mmol to 400 mmol) displayed longer infradian rhythm periods without parallel changes in body weight and extracellular water, and they were directly linked to urinary aldosterone excretion and inversely to urinary cortisol, researchers wrote. This suggests rhythmic hormonal control, they added. Thus, studies dependent on 24-hour urine samples to understand salt intake are not entirely accurate.
“We find these long rhythms of sodium storage in the body particularly interesting,” Titze said in the press release. “The observations open up entirely new avenues for research.”
Disclosure: Grants from the German Federal Ministry for Economics and Technology/DLR Forschung unter Weltraumbedingungen (50WB0920), the Interdisciplinary Centre for Clinical Research (IZKF Junior Research Group 2) supported the study.
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