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.
An unvaccinated child who went to the doctor with measles in Oakland, California, sends another baby to quarantine, leaving one mom to ask why. "Their choice endangered my child," she says.
Lethargic mice unexpectedly perk up when injected with immune cells from bullied mice, a discovery which could point to new depression treatments
People are able to read better when their visual processing is more sensitive to auditory information
The outbreak has so far claimed 8,795 lives across the affected West African region
Naked mole rats enjoy exceptionally long, healthy lives, and there's more than good genes at work
Scientists say impact of bringing forward girl’s first period by 2.7 months is likely to be modest
Melbourne-based study of children given nut protein with probiotic has transformed the lives of 80% of those who took part in clinical trial
Sunshine police take note, the latest guidelines from the UK's health advisory body NICE suggest we should actively seek out some rays
Choosing the viral targets for the seasonal flu vaccine is a gamble. Sometimes, like this year, the flu wins
Predicted lung cancer deaths for women in Europe set to reach 14.24 per 100,000 of population in 2015