Not so many moons ago …
That the moon somehow influences the behaviour and the physiology of humans has been a part of “folk knowledge” since time immemorial, but despite numerous investigations, tests, and analyses (and the frequent use of the term “lunatic”) there has not been any consensus on whether a “moon-effect” exists in humans at all. Yet, for quite a large number of in particular aquatic species of animals, the lunar cycle via its obvious cause of the tides is a fact: the Palolo worm Eunice viridis of the Pacific and the related Laor worm in Indonesian waters are famous examples; the coral Acropora millepora, the midge Clunio marinus and the grunion (sardine-sized fish of the genus Leurethes) are also species whose reproductive behaviours are linked to the lunar/tidal phase.
Would humans really be so different? After some extensive work, Rotto and Kelly in 1985 published the provocative statement that there was no thread of evidence to support the idea of a linkage between the lunar phase and human reproductive behaviour, activities or, moods and illnesses. Additional research by many others tended to agree – if there weren’t some odd exceptions. Contrary to a study in 1998 involving 50,492 non-fatal accidents in Saskatchewan (Canada) that did not demonstrate a link to the lunar cycle, Onozuka and co-workers in Japan, based on 842,554 traffic accidents in Kyushu (Japan) did show a significant increase on full moon nights, also seen with motorcycle-related deaths in the USA covering 40 years of data published in 2017. Näyhä in 2019, in contrast to earlier analyses elsewhere, showed that in Finland during full moon fewer homicides were committed than during the new moon phase and evidence for a lunar influence on patients suffering from bipolar disorders have recently been presented by the renowned psychiatrist Thomas Wehr.
Regarding suicides, the situation is no less confusing and the vast majority of the scientific publications on this topic, even the most recent ones of 2019, report that there is no evidence for a link between suicides and lunar phase. But did they miss perhaps something in their study? We followed up a 1973 investigation by K.P. and M.D. Ossenkopp, who reported that with self-inflicted injuries, women but not men showed a significant lunar periodicity. In our own study that involved 2111 male and 494 female suicide victims from the North-Finnish province of Oulu, we examined suicide occurrences during different lunar phases, compared the data with their expected distribution using multinomial tests with all tests being two-tailed, and separated the data according to the 4 seasons. No correlation between suicides and moon phase in any of the four seasons was apparent for male victims, but in winter for women it was. Further analysis revealed that the full moon association was statistically significant only for premenopausal women, defined as female victims younger than 45 years of age. To explain this unexpected finding a number of factors were considered, e.g., the darkness of a northern Finnish winter with increases of seasonal affective disorder, e.g. depression especially in premenopausal women, the influence of the lunar periodicity on the menstrual cycle, and cosmogeophysical effects. There is evidence from the earlier literature that older women are less-affected by season-bound depressions.
Although our study in Molec Psychiatry 2020, cannot confirm that lunar effects alone were indeed the reason for the winter full moon suicide peak in premenopausal victims, we cannot dismiss that pre- and post-menopausal women differ with regard to the menstrual period. That the moon in connection with cosmogeophysical factors like lunar phases and geomagnetic storms can affect calcium flux, melatonin, steroids, etc. is considered likely. The location of Oulu at latitude 65⁰N and its dark and long winter days could make it a rather unique setting for such a study. But then again: didn’t the famous astronomer Galileo totally dismiss the idea that the moon could be the cause of the tides – and was wrong?