Researchers from the University of Surrey have discovered that the effects of simulated microgravity can have a significant impact on the sleep patterns and rhythms of humans. This study suggests that these disruptions could have negative effects on the health and performance of astronauts in space.
Previous research has indicated that astronauts who undergo simulated microgravity through 60 days of continuous bed rest at a six-degree head-down tilt can experience disturbances in their physiological and sleep patterns.Muscle mass and bone density are reduced, and inflammatory responses are increased due to the changes in physiology that occur in microgravity. However, the effects of microgravity on sleep and biological rhythms are not as well-studied. Dr. María-Ángeles Bonmatí-Carrión, a post-doctoral researcher at the University of Surrey, who is currently at CIBERFES (Carlos III Health Institute), University of Murcia, and Principal Investigator at Murcian Institute of Biosanitary Research, stated that this study is the first to comprehensively evaluate sleep and various biological rhythms in a healthy individual in a microgravity environment.A 90-day study conducted at the MEDES space clinic in Toulouse, coordinated by the European Space Agency, involved 20 men who followed a protocol that included two weeks of baseline, followed by 60 days of continuous bed rest at a six-degree head-down tilt angle. This simulation aimed to replicate the effects of microgravity experienced by astronauts. The study’s findings are expected to contribute to the development of new protocols to enhance sleep and rhythmic stability in space. Additionally, the results may have implications for processes such as ageing and the impact of prolonged posture on sleep and rhythms.The study finished with a two-week recovery period. The research team analyzed wrist skin temperature, motor activity, light exposure, and diurnal sleepiness throughout the 90-day protocol to assess the effects of simulated microgravity. Sleep was evaluated using electroencephalogram (EEG) over a 24-hour period on two days at the start, three days during bed rest, and once in recovery. Saliva sampling was also done during these sessions to measure the phase and amplitude of melatonin, a hormone that regulates sleep-wake cycles, and cortisol, the body’s main stress hormone. The researchers observed a decrease in the amplitude of te
Researchers observed changes in temperature, activity, and sleep patterns during bed rest. Initially, sleep duration decreased, and on average, participants slept less than 6.5 hours per night throughout the study. The researchers pointed out that similar partial sleep deprivation has been linked to changes in immune system function and inflammation during both bed rest and spaceflight. Conversely, daytime naps increased, especially at the start of the study.
The results also supported the link between peripheral skin temperature and sleepiness, which was previously identified.
Temperature and melatonin secretion are affected even under conditions of bed rest. However, the relationship between peripheral temperature and different sleep stages is disrupted during bed rest, with wrist skin temperature increasing as sleep becomes deeper. This disruption could indicate a disturbance in thermoregulation processes related to sleep.
Professor Simon Archer, the senior author and Professor of Molecular Biology of Sleep at the University of Surrey, stated:
“Biological rhythms are disturbed, and sleep is limited in space flight, which has an impact on physiology and performance. The normal cycle of posture is a significant reinforcing signal for biological rhythms.”
The absence of gravity in space flight is likely a contributing factor to the reduction in rhythmic amplitudes of many variables studied in this protocol. These findings have significant implications for future space travel and for conditions where individuals are confined to long-term bed rest.”
Professor Derk-Jan Dijk, Director of the Surrey Sleep Research Centre, stated:
“Previous research in large cohorts, such as the UK biobank, has shown the predictive value of 24-hour rhythmicity amplitudes for future health. The current data highlight the importance of this aspect of human physiology and behavior.”
Behaviour can be affected by factors like extended bedrest and spaceflight.”
This research was printed in the publication npj Microgravity and was financially supported by the BBSRC. Further findings about the impact on gene expression in this study were recently released in iScience.
