There is a saying that when a full moon rises, like during Chuseok, emergency rooms get busier. Of course, it is only an "urban legend." According to research by U.S. scientists, the number of emergency room visits is not greatly affected by a full moon. That does not mean it is easy to say the full moon has no effect at all on health.
Moonlight affects hormone secretion and lowers sleep quality. When sleep, the best medicine, is reduced, health is bound to be affected. There are also studies finding that changes in hormones worsen epilepsy and mental health.
In 2013, a research team led by Professor Christian Cajochen at the University of Basel in Switzerland published findings in the international journal Current Biology that "when a full moon rises, sleep time decreases and sleep quality worsens." A survey of 33 adults found that when a full moon rose, total sleep time decreased by an average of 20 minutes. The intensity of delta waves—the brain waves that appear during deep sleep—fell by 30%.
The researchers said, "These changes are related to a decrease in melatonin levels." Melatonin is a hormone that induces sleep. It is secreted in the brain when it gets dark in the evening. In particular, it peaks between 2 and 4 a.m. If moonlight is bright, melatonin secretion is delayed, and the time spent falling asleep inevitably shrinks.
There are even findings that it becomes hard to fall asleep before the full moon rises. A research team led by Professor Horacio de la Iglesia at the University of Washington in the United States reported in Jan. 2021 in the international journal Science Advances that "3 to 5 days before a full moon rises, people fall asleep later than usual and total sleep time also decreases." The results are based on 1 to 2 months of sleep records from 98 Indigenous people from three tribes in northern Argentina. The researchers noted, "As moonlight gradually brightens, it interferes with falling asleep," adding, "However, the likelihood of waking people who are already asleep is low."
The researchers said artificial lighting plays a similar role to moonlight. The Indigenous groups in Argentina included a tribe with no lighting due to a lack of electricity, a tribe with limited lighting, and a tribe with city-like abundant lighting. As a result, the tribe without lighting fell asleep the earliest and had the longest sleep duration.
If a full moon changes hormones, mental health is also affected. In 2023, a research team led by Dr. Alexander Niculescu at the Indiana University School of Medicine in the United States reported in Discover Mental Health that "an analysis of 776 people who died between 2012 and 2016 showed a higher likelihood of suicide on full moon days." The researchers said, "Those 55 and older are particularly at risk."
Beyond that, the most dangerous time was 3 to 5 p.m. The researchers said this is because cortisol decreases as sunlight wanes. Cortisol is a hormone that rises to help overcome stress. Cortisol secretion is highest at 6 a.m. From 3 p.m., cortisol decreases and can affect stress regulation.
There are also studies finding that a full moon increases the risk of epilepsy. In 2008, a research team led by Professor Christine Paule and Professor Mark Quigg of the University of Virginia reported in the international journal Epilepsia that "around the time of a full moon, the number of patients with seizures increases." An analysis of four years of hospital records led the researchers to conclude that when moonlight is strong, hormones change and influence seizures.
The saying that ambulance sirens rise when a full moon appears is nothing more than a myth. Even so, scientists remain interested in the link between lunar cycles and health because there is still much we do not know about the human body and mind. By the next Chuseok, new effects of the full moon on the human body may be revealed.
References
Current Biology (2013) : https://www.cell.com/current-biology/fulltext/S0960-9822(13)00754-9?_returnURL=https%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS0960982213007549%3Fshowall%3Dtrue
Science Advances (2021), DOI : https://doi.org/10.1126/sciadv.abe0465
Discover Mental Health (2023) : https://link.springer.com/article/10.1007/s44192-023-00035-4
Epilepsia (2008), DOI: https://doi.org/10.1111/j.1528-1167.2008.01537.x