The Full Moon Might Be Affecting Your Sleep and Menstrual Cycles, Studies Find

Believers in astrology associate the lunar cycle with severe changes in people’s mood, blaming a full moon for making them feel all types of emotions, from anxious to violent. If Greek and Roman mythology is to be believed, the occurrence of the full moon also makes people do all sorts of crazy things, including transforming into werewolves and howling at the moon. But while science is yet to substantiate any of these beliefs, a new study has found that the full moon might be affecting your sleep cycle.

Published in the Science Advances journal, the study found that in the days leading up to the full moon, people go to bed later and get less sleep. Participants were observed to go to bed approximately 30 minutes later and lost out on 50 minutes of sleep the night before a full moon, said study co-author Horacio de la Iglesia, professor at the department of biology at the University of Washington in Seattle, U.S.

The sleep schedule of each participant was tracked using a wrist monitor over one to two lunar cycles, each of which lasts for about 29.5 days. The sample size consisted of 98 people from three different Toba Indigenous communities in rural Argentina, also known as the Qom people.

Study co-author Leandro Casiraghi, postdoctoral scholar at the department of biology at the University of Washington, said that the moon emits brighter light after sunset on the days leading up to the full moon. 

"We believe this modulation aims to take advantage of such moonlit nights which may be good for safe outdoor activities such as hunting or fishing, or for engaging in social interactions with other groups," Casiraghi told CNN.

The human body has had to adapt to exposure to light and dark over centuries, leading to the development of a circadian rhythm, an internal clock that regulates sleep for about a 24-hour period. This controls the human body in many ways, including the body’s sleep-wake cycle. With the invention of electric light, however, our circadian rhythms have had to begin this adaptation process all over again.

To control for these factors, the scientists made sure that three different groups of rural participants received varied access to electricity. While one group had no access, another had limited access, and the third had full access to electricity. Regardless of which group they were in, a strong pattern was observed in how participants went to bed late and logged less sleep in days leading up to the full moon. Depending on the community, the total amount of sleep varied across the lunar cycle by an average of 46 to 58 minutes, and bedtimes varied by around 30 minutes. These results were then placed aside results from 464 college students at the University of Washington.

These urban residents went to bed even later and slept less than their rural counterparts. This came as a surprise to Casiraghi, who had hypothesised that only participants in the rural setting would be affected by the phases of the moon. 

“We hypothesise that the patterns we observed are an innate adaptation that allowed our ancestors to take advantage of this natural source of evening light that occurred at a specific time during the lunar cycle,” he said.

Past research has also connected the phases of the moon to the human sleep cycle. In 2005, psychiatrist David Avery suspected that the moon and its gravitational pull on the Earth were severely affecting a patient’s sleep cycle, ranging from near total insomnia to getting a good 12 hours of sleep in a night. A 2013 study conducted in a highly-controlled environment also found that participants took five more minutes to fall asleep and slept 20 minutes less in the days leading up to the full moon. Even when they weren’t exposed to any moonlight, the amount of deep sleep they experienced dropped by almost 30 percent.

The findings of the recent study also suggest that lunar phases affect human slumber regardless of ethnicity, socio-cultural background, or even the geographical location.

“We humans tend to believe that we managed to somehow control nature, and the use of artificial light is a great example of that. But it turns out that there are some forces of nature that we cannot get away from,” said de la Iglesia.

Our sleep cycle is not the only bodily system the moon can possibly control though. Another new study published in Science Advances has found that the lunar cycle has a connection with people’s menstrual cycles. 

By analysing menstrual cycle records that 22 women kept for up to 32 years, it was seen that cycles lasting longer than 27 days were “intermittently synchronised with cycles that affect the intensity of moonlight.” As the participants grew older, this connection seemed to become weaker, also affected by increased exposure to artificial light.

However, scientists have denied any link between the two in the past, hinting that the two cycles might just be similar in length. 

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