The appeal of exploration and discovery is innately human. It is a unique human desire to learn about the world and beyond. As Captain James T. Kirk famously said, space is the final frontier. From children to billionaires, the stars hold a mystifying power. However, before humanity can properly explore the universe, some biological hurdles must be conquered. One of these hurdles is the circadian rhythm.
The circadian rhythm is the natural 24-hour
oscillation of biological processes in organisms. Simply put, it is the body’s
biological clock that regulates molecular and biochemical pathways. For humans,
it is fundamentally linked to the Earth’s rotation and received sunlight. The
brain’s master clock, the suprachiasmatic nucleus of the hypothalamus, receives
photic information from the eyes and uses this data to coordinate the biological
processes of the human body. Without a proper light-dark cycle, the body could run
into quite a few problems.
Circadian desynchrony has been linked
to cardiovascular disease, metabolic disease, gastrointestinal disease, and
cancer. It increases the chances of diseases developing, worsens disease severity,
and exacerbates disease progression (Summa & Turek, 2014). Not only that,
but circadian disruption can also negatively affect mood regulation and mental
health (Walker et al, 2020). Although most data between circadian rhythm
disruption and psychopathology are correlational, it can be summed up that
circadian disruption can elicit and exacerbate mental health disorder symptoms.
If circadian dysregulation negatively
affects the human body on Earth, how much more would it be in space? One significant
difference between Earth and the environment of space is light exposure.
According to Space Center Houston, the International Space Station, orbits
around the Earth every 90 minutes. That is a light-dark cycle with a period of
1.5 hours. Such a dramatic change from Earth’s 24-hour period must reap
terrible repercussions!
Fortunately, scientists are exploring
the effects of space flight on astronauts. Dr. Jun Hirayama and his colleagues studied
the physiological consequences of exposure to the space environment. They
discovered that the abnormal light exposure and microgravity in space reduced
the level of melatonin synthesized by the pineal gland (Hirayama et al,
2023). This hormone is the body’s biochemical signal for darkness. This imbalance
leads to circadian clock misalignment and ultimately contributes to the pathophysiological
conditions of astronauts.
Thankfully, the research Hirayama
et al conducted points to melatonin regulation as a possible therapeutic option
not just for circadian desynchrony in space, but also for abnormal bone
metabolism and as radiation protection (Hirayama et al, 2023). Knowing
the importance of melatonin production in the body means that proper light-dark
conditions need to be made for space flight to be safer.
However, human ambition knows no
bounds and there’s more to the universe than just space! There are also planets
and Mars is in the spotlight. Luckily, when it comes to light exposure, Mars’
light-dark cycle is not that different from Earth's. A day on Mars is 24 hours
and 37 minutes long. This means that circadian dysregulation might not be as
bad on Mars as it is on the ISS (Meek, 2018). This does not mean that a colony
on Mars is close at hand, there are still plenty of challenges to overcome. Nonetheless,
the possibility is there and that is all the motivation humanity needs to
boldly go where no one has gone before.
References
Admin. (2019, November 19) Sleeping
with the lights on. Space Center Houston. Retrieved February 29, 2024, from
https://spacecenter.org/sleeping-with-the-lights-on/#:~:text=A%20day%20on%20station&text=The%20ISS%20orbits%20Earth%20every,sunrises%20and%20sunsets%20each%20day!
Hirayama, J., Hattori, A., Takahashi, A., Furusawa, Y., Tabuchi, Y., Shibata, M., Nagamatsu, A., Yano, S., Maruyama, Y., Matsubara, H., Sekiguchi, T., & Suzuki, N.(2023). Physiological consequences of space flight, including abnormal bone metabolism, space radiation injury, and circadian clock dysregulation: Implications of melatonin use and regulation as a countermeasure. Journal of Pineal Research, 74(1), e12834. https://doi.org/10.1111/jpi.12834
Meek, H. (2018, November 14). Ask A Scientist: How does space travel affect circadian rhythms? The Daily Beacon. Retrieved February 29, 2024, from https://www.utdailybeacon.com/opinion/columns/ask-a-scientist-how-does-space-travel-affect-circadian-rhythms/article_29a4c82e-e863-11e8-ac22-a742d8a14119.html
Summa, K. C., & Turek, F. W.
(2014). Circadian desynchrony and health. Atlas of Clinical Sleep Medicine.
https://doi.org/10.1016/b978-0-323-65403-6.00029-9
Walker, W.H., Walton, J.C., DeVries, A.C., & Nelson, R.J. (2020). Circadian rhythm disruption and mental health. Translational Psychiatry 10(28). http://doi.org/10.1038/s41398-020-0694-0
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