The moon gets a lot of guilt and guilt for human activities, but on examination most claims turn out to be merely astrology; good stories without reliable evidence. Nevertheless, two recently published studies find statistically significant evidence for lunar effects on two old favorites, sleep and menstruation, although partially suppressed by electric lights.
Professor Horacio de la Iglesia of the University of Washington gave 98 members of Toba-Qom indigenous communities in Formaosa Argentina sleep tracking and compared their sleep pattern with the amount of moonlight.
The Toba-Qom was chosen because many live in communities with little or no access to electricity. With more opportunities to do things after the sun went down, this group later went to sleep and slept less as the moon approached full. Even in urban areas, where street lights exceed the moon, sleep has also been reduced, reports de la Iglesia in Science Advances.
Toba-Qom participants slept 46-58 minutes more in the dark of the moon as when it was almost full and fell asleep about 20 minutes later.
Horacio de la Iglesia uses sleep data from 464 students at the University of Seattle collected for another study to examine its findings. “While the effect is more robust in communities without access to electricity, it is an effect in communities with electricity, including undergraduate students at the University of Washington,” he said in a statement.
In light of these observations, it is almost strange that attempts to confirm the link between the full moon and crime or car accidents have been unsuccessful.
Toba-Qom with little or no electricity also showed what de la Iglesia calls a ‘semilunar’ 15-day sleep cycle. Although he is not sure about the cause, he thinks it may be related to gravity effects, which are stronger than the gravity of the sun and moon in line twice a month.
The same issue of Science Advances contains another article by one of the same authors examining the influence of the moon on menstruation. The fact that the typical menstrual cycle so closely corresponds to the time between one full moon and the next, has long been accepted that it is not accidental.
“In many marine species and some terrestrial species, reproductive behavior is synchronized with a particular phase of the lunar cycle,” the article says. Great coral casting events are a particularly dramatic example. Yet it was not clear whether humans had a similar evolutionary advantage, or that the period was merely a legacy of our origin, which had long since ceased to be linked to the phases of the moon.
Previous studies reported that 28 percent of women who menstruate regularly have cycles that last within a day of the 29.5-day length of the lunar cycle – a minority but a much greater concentration than at any other number of days. In addition, 28-29 day periods are associated with a greater chance of fertilization. Investigations into whether menstruation is particularly consistent with a specific lunar phase, however, have yielded conflicting results.
Lead author Professor Charlotte Helfrich-Förster of the University of Würzburg used only 22 women’s records to investigate this issue, much less than previous studies, but over a much longer period of time. Participants recorded their periods for up to 32 years, along with details about their sleep conditions, such as exposure to artificial light.
Before the age of 35, participants had 23.6 percent of the time periods synchronized with the moon. After 35, it dropped to just 9.5 percent, reflecting a decline in the average period to 26 days. Synchronization was much more common for those who lived in the countryside and went to bed early than those who were more exposed to artificial light. The most common phase to match was shortly before full time, when the evening light is greatest.
Helfrich-Förster also found a weak correlation between gravitational peaks and menstrual cycles, which according to de la Iglesia’s theory light is not the only way to influence us.