How the moon phases affect sleep and menstrual cycles

The Moon receives a lot of credit and blame for human activities, but upon investigation most of the claims turn out to be mere astrology; good stories lacking reliable evidence. Nonetheless, two recently published studies find statistically significant evidence of lunar effects on two old favorites, sleep and menstruation, although partially suppressed by electric lights.

University of Washington Professor Horacio de la Iglesia gave sleep-tracking wristwatches to 98 members of the Toba-Qom indigenous communities of Formaosa in Argentina, and compared their sleep patterns with the amount of moonlight. .

The Toba-Qom were chosen because many live in communities with little or no access to electricity. With more opportunities to do things after sunset, this group went to bed later and slept less as the moon approached. Even in urban areas, where streetlights eclipse the moon, sleep was also reduced, de la Iglesia reports in Science Advances.

The Toba-Qom participants slept 46 to 58 minutes longer in the darkness of the Moon as when it was nearly full, falling asleep about 20 minutes later.

Horacio de la Iglesia used sleep data from 464 Seattle-area students collected for another study to verify his results. “While the effect is more robust in communities without access to electricity, the effect is present in communities with electricity, including undergraduates at the University of Washington,” he said. he said in a statement.

In light of these observations, it is almost strange that efforts to confirm the links between the full moon and crime or car accidents have not been more successful.

Toba-Qom with little or no electricity also showed what de la Iglesia calls a 15-day “semilunar” sleep cycle. While unsure of the cause, he believes it may have to do with gravitational effects, which are stronger when the gravity of the Sun and Moon aligns twice a month.

The same edition of Science Advances contains another article, with one of the same authors, exploring the influence of the Moon on menstruation. The fact that the typical menstrual cycle so closely matches the time between one full moon and the next has long been assumed not to be a coincidence.

“In many marine and some land species, reproductive behavior is synchronized with a particular phase of the lunar cycle,” the document notes. The immense coral spawning episodes represent a particularly dramatic example. Still, it’s not clear whether humans have a similar evolutionary advantage, or whether the length of the period is just a legacy of our ancestry, long uncoupled from the phases of the Moon.

Previous studies have reported that 28% of women who menstruate regularly have cycles that last less than a day past the 29.5-day lunar cycle – a minority, but a much higher concentration than any other number. days. In addition, periods of 28 to 29 days are associated with a higher probability of conception. However, research into whether menstruation is particularly likely to align with a specific moon phase has produced conflicting results.

Lead author Professor Charlotte Helfrich-Förster of the University of Würzburg used only 22 women’s files to explore this question, far less than previous studies, but over a much longer period. Participants recorded their periods up to age 32, along with details of their sleep conditions, such as levels of exposure to artificial light.

Before the age of 35, participants had periods synchronized with the Moon 23.6% of the time. After 35 years, this percentage fell to just 9.5%, reflecting a decrease in the average period length to 26 days. Synchronization was much more common in people living in rural areas and going to bed early than in people more exposed to artificial light. The most common phase to associate was shortly before full, when the evening light is strongest.

Helfrich-Förster also found a weak correlation between gravitational peaks and menstrual cycles, corresponding to the Iglesia theory, light is not the only way the Moon influences us.