Maintaining the right sodium levels in the body is crucial for controlling blood pressure and ensuring proper muscle function. Conventional wisdom has suggested that constant sodium levels are achieved through the balance of sodium intake and urinary excretion, but a new study in humans published by Cell Press on January 9th in the journal Cell Metabolism reveals that sodium levels actually fluctuate rhythmically over the course of weeks, independent of salt intake. This one-of-a-kind study, which examined cosmonauts participating in space-flight simulation studies, challenges widely accepted assumptions that sodium levels are maintained within very narrow limits.
"The study highlights the importance of measuring salt excretion in urine over a longer time period to accurately estimate salt intake," says senior study author Jens Titze of Vanderbilt University School of Medicine. "This information is very important, given the emphasis on salt intake in terms of risk for cardiovascular disease and healthcare outcomes."
Past studies in humans have shown that when dietary salt intake increases, a steady state of sodium levels in the body is achieved through rapid urinary excretion. This process is under the control of a hormone called aldosterone, which causes sodium to be retained in the kidneys. However, most of these studies were short-term and did not examine fluctuations in sodium levels in response to constant salt intake.
To address these limitations, Titze and his team took advantage of a unique opportunity to control salt intake and study salt balance over the course of nearly seven months in 12 male participants in the Mars105 and Mars520 studies. These men spent 105 and 520 days, respectively, in an enclosed habitat consisting of hermetically sealed interconnecting modules at a spaceship simulation facility in Moscow, where they lived and worked as if they were cosmonauts at the international space station. As expected, their aldosterone levels increased when they consumed less salt. But surprisingly, a decrease in salt intake led to a reduction in levels of the "stress hormone" cortisol.
When the researchers kept salt intake constant, sodium excretion and the levels of aldosterone and cortisol fluctuated together in weekly cycles. On the other hand, sodium levels in the body exhibited longer-term rhythmic changes that were independent of salt intake. Over this longer timescale, elevated sodium levels were associated with high aldosterone levels and low cortisol levels, suggesting that the two hormones work in opposite ways to control sodium storage and release.
"To the best of our knowledge, the long-term rhythm we observed in sodium levels in the body has not been previously reported, and it was not known that cortisol and aldosterone work in opposite directions to regulate sodium metabolism," Titze says.
Cell Press: http://www.cellpress.com
This press release was posted to serve as a topic for discussion. Please comment below. We try our best to only post press releases that are associated with peer reviewed scientific literature. Critical discussions of the research are appreciated. If you need help finding a link to the original article, please contact us on twitter or via e-mail.
From Dr Strangelove and water fluoridisation to climate change, scientific method and facts are not always enough to win over the sceptics
On a blog post at PLOS, the tropical disease expert Peter Hotez and postdoctoral fellow Jennifer Herricks take a run through the data on the biggest killers of children around the world in 2013, part of a new dataset from Global Burden of Disease study published in the January Lancet.
Tory MP David Tredinnick seems to believe that astrology could inform and improve UK healthcare. This view is misguided and potentially dangerous
Resistance to vital antimalarial drugs called artemisinins has spread across Burma to the Indian border. If not contained, it could ultimately hit Africa hard
Clostridium difficile sickens nearly half a million Americans annually, killing about 29,000, say federal health officials. They warn hospitals and nursing homes to tighten hygiene protocols.
Study looking at transmission among men who have sex with men recruited 545 participants at high risk of contracting HIV A daily pill can effectively protect gay men against infection with HIV
An experimental therapeutic vaccine from Danish drugmaker Bavarian Nordic helped significantly extend survival in patients with advanced prostate cancer, according to results of a small early-stage trial conducted by the U.S. National Cancer Institute.
Scientists interviewed more than 1,000 men, women and children who were forced into sex work and hard labor. The result is the largest study to detail the health of human trafficking survivors.
Gerbils from Asia rather than black rats were responsible for repeated outbreaks of the bubonic plague in Europe, a study suggests.
The so-called "cuddle-chemical" seems to block the action of alcohol in the brain, preventing the tell-tale signs of drunkenness in rats