All living things (including humans, plants and animals) have photoreceptors which recognize the difference between light and dark cycles. These light cues (known in the sleep world as zeitgebers), help us to stay awake during the day and to fall asleep at night. Melatonin production in the brain increases as the sky darkens in the afternoon, then drops off dramatically with the first peek of daylight in the morning.
Astronauts, however, have a different relationship with sunrises and sunsets while working on the International Space Station, where the sun rises and sets every 90 minutes. This rapidly shifting rhythm of light to dark can seriously impose itself on the human circadian system, which is entrained to 24-hour days. Over time, this can lead to hormonal confusion in the brain and, ultimately, insomnia for these space walkers.
Insomniac astronauts are not a good idea. What this could mean is that, during their waking hours, these sleep-deprived astronauts may share a common risk-taking behavior with long-haul truckers, bus drivers and airline pilots: drowsy driving. Lack of quality sleep can result in poor judgment, inability to achieve an appropriate level of alertness in emergency situations, even the opportunity to "sleep drive" (like sleepwalking, but while driving).
Most astronauts end up taking Ambien (aka zolpidem as a generic) to regulate their sleep cycles and comply with their daily requirement of 8.5 hours of sleep, but Ambien can leave them with a foggy morning-after hangover that can impair their performance nearly as much as sleep deprivation. It can also be to blame for some unusual behaviors that can occur while asleep which are typically hallucinatory in nature and may resemble sleep walking.
So which is better... sleep deprived astronauts or hallucinating ones?
Dr Charles Czeisler, a Harvard Medical School sleep expert who co-authored a recent article for Lancet about the problem of sleep for astronauts, said: "Future exploration spaceflight missions to the moon, Mars, or beyond will require more effective countermeasures to optimize human performance by promoting sleep during spaceflight... These may include modifications to schedules, strategically timed exposure to specific wavelengths of light, and behavioral strategies to ensure adequate sleep, which is essential for maintaining health, performance and safety."
So really, the answer is neither. Humans need sleep, even and, perhaps, especially, those who don't have their feet solidly planted on the terra firma.
- Sleeping pills in space: Astronauts are regular users || USA Today
- What it's like for astronauts to sleep in space || The Atlantic
- Sleep, the final frontier: Astronauts suffer serious insomnia while in space - and it could be putting their lives in danger || The Daily Mail (UK)
*Ambien is popularly referred to as "the walrus" after a comic strip artist began to write about Ambien experiences in which a "walrus" told him things while he was under its influence.