Lunar cycles and human behavior.The Problem
Your partner hands you the on-call pager and wishes you good luck. You wonder what he means until you realize that the night sky will be illuminated by a full moon. You wonder whether Shakespeare was right and whether you are in for it: "It is the very error of the moon; She comes more nearer earth than she was wont; And makes men mad ..." (Othello, Act 5, Scene 2).
Do lunar cycles affect human behavior?
We first searched the Cochrane Database of Systematic Reviews (www.cochrane.org/reviews) and found no reviews. We then searched Medline combining "lunar or moon" and "behavior."
The notion that stars and planets influence unusual or deviant human behavior can be traced to Roman times. Even among mental health professionals, there is a common belief that lunar cycles influence human behavior (J. Psychosoc. Nurs. Ment. Health Serv. 2000;38:29-34).
An early meta-analysis looked at data from 37 studies examining the relationship between phases of the moon and different types of "lunacy," including psychiatric admissions, psychiatric disturbances, crisis calls, suicides or self-harm, homicides, and other types of criminal activity (Psychol. Bull. 1985;972:286-306). The total number of psychiatric admissions looked at were 89,973 over 467 lunar cycles, 5,575 psychiatric disturbances over 477 cycles, 43,177 crisis calls over 148 cycles, 32,273 suicides or self-harm incidents over 343 cycles, 29,126 homicides over 599 cycles, and 535,836 criminal offenses over 229 cycles. The authors found that the phases of the moon accounted for no more than 1% of the variance in human behavior.
Scottish researchers looked at the correlation between 20,919 acts of self-injurious behavior in patients aged 16 or older over 222 lunar cycles (Psychol. Med. 1991;21:393-7). A sine-wave curve of self-injurious behavior was found, but without correlation to lunar cycle.
Spanish investigators looked at the association between motor vehicle crashes and lunar cycles (Percept. Mot. Skills 1993;77:371-6). A total of 4,835 accidents occurred over 48 lunar cycles. No relationship was found between lunar cycle and the number of accidents when analyzed for the entire period.
Psychologists in Massachusetts looked at the relationship between lunar cycles and the occurrence of psychiatric hospital admission of developmentally disabled adults (Psychol. Rep. 1994;75:1435-40). A total of 86 community-based, developmentally disabled adults were followed over 35 lunar cycles. No correlation was found between lunar cycles and admissions.
Researchers in a British seaside town followed 100 patients through 30 lunar cycles (J. Psychosoc. Nurs. Ment. Health Serv. 2000;38:29-34). When the study was conducted, the possibility of a lunar effect was not considered. A total of 100 patients were assessed 4 times over the 30 lunar cycles using the Brief Psychiatric Rating Scale (BPRS) and the Lancashire Quality of Life Profile. Of the 100 patients, 56 were diagnosed with schizophrenia, 33 with a mood disorder, and 11 patients with mixed diagnoses. No significant correlations were found between psychopathology and lunar cycles except in the schizophrenia group: The BPRS subscale for hostility increased significantly during full moons.
British researchers also evaluated the correlation between self-inflicted burns over a 20-year period (Burns 2004;30:833-5). During this period, 7,139 patients were admitted to the burn unit, of which 184 were identified as having self-inflicted burns. The mean age was 37 years. Analysis failed to show a connection between self-inflicted burns and lunar cycles.
In Louisiana, researchers looked at telephone records from a crisis center over a 6-month period (J. Soc. Psychol. 1990;130:47-51). The timing of 4,575 crisis calls was examined, and no correlation was found between crisis calls and lunar cycle.
The U.S. Navy looked at the correlation between psychiatric admissions and phases of the moon between September 1993 and June 2001 (Mil. Med. 2006;171:1239-42). Records from the Naval Medical Center in San Diego were examined from 8,473 admissions. Diagnoses were classified as psychotic disorder, mood disorder, anxiety disorder, and other. The author concluded that "no statistically significant effect of the lunar cycle was seen on psychiatric admissions or evaluations of any kind."
Researchers in Germany evaluated the association between self-poisoning and lunar cycles (Psychiatr. Res. 2008;161:177-84). Data were obtained retrospectively from an intensive care unit in Heidelberg between January 2002 and December 2004. A total of 691 patients were included for the analysis. Mean age was 39 years. No relationship between lunar cycle and self-poisoning was found.
Shakespeare was a great man, but the evidence does not back him up in the case of the moon and madness. Evidence overwhelmingly shows that there is no correlation between human behavior and lunar cycles. So why is this belief so strong? One author offers a hypothesis: Until the availability of domestic and street lighting, moonlight, especially around the days of a full moon, would have permitted many activities, including social gatherings. Perhaps, this belief arose because sleep disruption, which affects illnesses such as bipolar disorder, would have occurred in societies regulated by lunar illuminance (Curr. Biol. 2008;18:R784-94).
Dr. LEARD-HANSSON is a forensic psychiatrist who practices in San Diego. Dr. GUTTMACHER is chief of psychiatry at the Rochester (N. Y.) Psychiatric Center. They can be reached at firstname.lastname@example.org.