For the study, the scientist outfitted participants with sleep monitors on their wrists to track their sleep over one or two lunar cycles. One lunar cycle is 29.5 days.
The participants were members of three Western Toba/Qom communities of the Argentinian province of Formosa. One community was in an urban setting with full access to electricity, and two were rural communities, one with access to limited electric light and the other with no access to electric light at all.
Because the moon is brighter in the days leading up to a full moon, study co-author Leandro Casiraghi told CNN, ““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.”
Regardless of access to electricity, the sleep patterns in each community were similar, which surprised the researchers. They had hypothesized only participants in areas without artificial light would be affected.
“The fact that this modulation was present even in communities with full access to electric light suggests that these effects are mediated by something other than moonlight itself,” Casiraghi told CNN.
The scientists then compared the Argentina results with those of 464 Seattle students being tracked for another study and found similar patterns.
If you have trouble sleeping, study co-author Horacio de la Iglesia told CNN you should avoid bright lights and screens in the evening and be “especially proactive before a full moon when ‘most people are predisposed (to) have a delayed sleep start and a shorter sleep.’”