Space Oddity: Use of Sleep Aids in Astronauts Astronomical

Pauline Anderson

August 12, 2014

Sleep deficiency is pervasive among astronauts before and during space flight, and the reported incidence of sleep-promoting medication use is 20 times greater than the proportion of Americans estimated to use hypnotic drugs at any time in a given year, new research shows.

The findings underscore the importance of understanding the effect of space travel on sleep as scientists explore further beyond Earth and the role of sleep-enhancing aids while in space.

"Use of sleep drugs during spaceflight needs further investigation to develop and recommend best practices for crew members aboard the ISS [International Space Station], and in missions beyond low Earth orbit," the authors, led by Laura Barger, PhD, Division of Sleep and Circadian Disorders, Department of Medicine and Neurology, Brigham and Women's Hospital, Boston, Massachusetts, write.

The study was published online August 8 in Lancet Neurology.

To Mars and Beyond

Researchers used data collected by actigraphy during in-flight and throughout pre- and postflight intervals: 2 weeks 3 or so months before the launch, 11 days before the launch day, and for the first 7 days after landing.

Crew members continuously wore a small, light-weight device (Actiwatch-L, MiniMitter) on their nondominant wrist. The device recorded activity and data for light exposure. Crew members also kept a log of daily sleep and medicine use.

The researchers used a standard algorithm to analyze data on more than 4000 nights of sleep on the ground before and after space flight and on more than 4200 nights in space among 85 astronauts (64 on Space Transportation System shuttle missions and 21 aboard ISS missions) before, during, and after spaceflight.

NASA schedules 8.5 hours of sleep per night for crew members in spaceflight. Quiet and darkened "sleep stations" have been installed on the ISS.

Researchers found that sleep time averaged 5.96 hours during shuttle missions and 6.09 hours during ISS missions. The sleep time was 6.04 and 5.86 hours, respectively, during prelaunch for these missions.

This prelaunch sleep deficiency isn't dissimilar to sleep loss often reported with stress before important events, such as exams, athletic events, or difficult work, the authors note.

About three quarters (78%) of shuttle crew members reported taking sleep-promoting drugs in-flight. Use of such drugs was reported on 52% of the 963 in-flight shuttle nights. Two doses of sleep drugs were taken on 17% of 500 nights on which such drugs were taken.

"The reported incidence of sleep-promoting drug use during spaceflight is 20 times greater than the proportion of Americans estimated to use hypnotic drugs at any time in a given year," noted the authors.

Zolpidem and controlled-release zolpidem were the most frequently used drugs on shuttle missions, accounting for 73% and 12% of the 413 nights, respectively, when 1 dose of drug was reported.

Taking these sleep aids increased sleep efficiency on average by only 1.3%. This, write the authors, "emphasizes the need for better counter measures and for further investigation into the stability, absorption and effectiveness of such drugs in-flight."

The marginal benefit offered by sleep aids should be balanced against the risks of hypnotic drugs, which can include reduced performance while operating spacecraft, said the authors.

They note that the US Food and Drug Administration (FDA) has warned against patients taking these drugs while engaging in occupations that require mental alertness or motor coordination and using these medicines when they can't get a full night's sleep.

The researchers also pointed out that the FDA black-box warning on all hypnotic drugs states that driving and performing other tasks might be impaired the morning after use of such drugs.

Further research of sleep is planned for the future 1-year ISS missions, which is twice the length of the current ISS missions. The new research "might provide information on trends in sleep over longer duration, which is especially relevant for future exploration missions to Mars and beyond."

Marginal Benefit

In an accompanying editorial, Mathias Basner, MD, PhD, assistant professor, Sleep and Chronobiology, and David Dinges, PhD, professor, psychology, Department of Psychiatry, University of Pennsylvania, Philadelphia, also argued for studies of longer duration.

"We do not know what will happen to sleep or the biological functions it serves when human beings stay in space for a prolonged period of time," they write. "Space exploration requires that we answer that fundamental question."

Factors possibly adversely affecting sleep in space include noise, physical discomfort, non-24-hour light-dark cycles, hypoxia and hypercapnia, and psychological factors related to living in an isolated, confined, and extreme environment, according to the editorial.

Dr. Basner and Dr. Dinges noted that microgravity requires that astronauts sleep in bags "tethered to a wall" and that this can cause back pain and fluid shifts associated with increased intracranial pressure. High workload during premission training and during spaceflight can contribute to chronic sleep curtailment and use of sleep-promoting drugs, they write.

A limitation of the study was that actigraphy doesn't directly measure sleep stages so the authors were unable to detect differences in sleep structure associated with sleep promoting drugs. However, actigraphy is highly correlated with polysomnographically defined sleep timing, even under spaceflight conditions.

Also, because the study was observational, it was unable to capture objective measures of cognitive or operational performance or errors.

Dr. Barger has previously received research support from Cephalon (nonpublic sponsors of research) and consults for Alertness Solutions and San Jose State University Foundation. Dr. Basner and Dr. Dinges report grants from NASA and the National Space Biomedical Research Institute for topics related to the submitted work, and grants from National Institutes of Health the US Office of Naval Research, outside the submitted work.

Lancet Neurol. Published online August 8, 2014. Abstract  Editorial


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