Two recent papers on lunar influence were recently published in the journal Science Advances. They made some buzz but do not really advance science.

Moon and Sleep

Leandro Casiraghi et al. (2021) asked twenty-five to forty people in each of three Argentine villages (one rural without access to electricity, one semi-rural, and another in an urban area) to record when they went to sleep and when they awoke during two consecutive months. The rural people reported that they went to sleep about twenty-five minutes later (and their sleep was shortened by about the same amount of time) just before the full moon. The effect was smaller—likely insignificant—for urban people. The obvious explanation, which was confirmed by subsequent interviews: people in rural areas stayed awake later when there was more (moon)light.

The authors claimed to have found a similar difference in students from the University of Washington, but details are so scarce that its validity cannot be determined. Indeed, several previous studies have failed to find any difference in sleep duration with lunar phase when using representative samples. Finally contradicting their own results, the authors postulated gravity, not light, as the cause—but gravitational (tidal) effects would be maximal at both full and new moons, which occur bimonthly, not monthly. They explained the discrepancy by saying only the full moon can be “above” the sleeper and “pull,” which is nonsense (remember tidal bulge geometry!).

Moon and Menstruation

The other article, by C. Helfrich-Förster et al. (2021), claims to find a link between menstruation and lunar phases. Its small sample (only twenty-two subjects) was unlikely to have enough statistical power to be meaningful, and in any event the results were actually negative! In ten subjects there was no correlation, and for the others the correlations were only intermittent. Also, there were many woman-to-woman differences (e.g., their evolution with age or the relevant phase—full or new moon). Their data failed to support their conclusion of “high synchrony,” and, moreover, the authors’ supporting references were cherry-picked to support their hypothesis. In the end, a last claim about the impact of light pollution (used to explain differences with an older, also problematic, “study”) is not backed-up.

Finally, that paper ended by saying that the cause for synchronization was gravitation—specifically tides. They propose that humans can sense tidal atmospheric pressure changes or oscillation that electromagnetic fields create by a perturbed magnetotail. In addition to repeating that women are not lunar clocks, is it necessary to say that none of those detection capabilities were ever found?

These studies in Science Advances can be disregarded. The moon was once thought to cause madness and many other strange effects. Despite numerous studies over many years, science has found no credible evidence of correlation between lunar phases and human biology.

Acknowledgment

The author thanks Dr. Harriet Hall for her help in shortening this article and her advice on the manuscript.

References

Casiraghi, L., Ignacio Spiousas, Gideon P. Dunster, et al. 2021. Moonstruck sleep: Synchronization of human sleep with the moon cycle under field conditions. Science Advances 7(5). Available online at https://advances.sciencemag.org/content/7/5/eabe0465.

Helfrich-Förster, C., S. Monecke, I. Spiousas, et al. 2021. Women temporarily synchronize their menstrual cycles with the luminance and gravimetric cycles of the Moon. Science Advances 7(5). Available online at https://advances.sciencemag.org/content/7/5/eabe1358.