I’ve held the belief that the moon cycle affects sleep cycles and subsequent mental health and human behaviour. This stems back to my days working in hospitals, usually from doing overnight shifts in Emergency Departments. If there was a particularly busy, chaotic or just downright weird shift then it would always seem to correlate with a full moon. There are obviously many biases in this notion. Let’s see what the evidence says.

TL;DR = meta-analyses found no strong evidence. Small studies show changes in sleep patterns. Changes in sleep affect mental health conditions such as Bipolar Disorder.

Overall meta-analysis showed no correlation.

• In 1985 a meta-analysis of 37 studies and found that the phases of the moon accounted for no more than 1% of the variance in activities usually termed lunacy.

No evidence of increased crisis calls.

• In 1992 Byrnes and Kelly reviewed 12 studies conducted over 20 years that looked at the number of crisis calls and their correlation to the phases of the moon. They found no evidence of a trend associated with moon phase and concluded that the full moon was not associated with a higher frequency of calls reporting disturbing behaviour.

No evidence of increased suicide.

• Also in 1992, a critical review of 20 studies done over 28 years linking suicide and the lunar phase concluded that most studies showed no relation between the lunar phase and measures of suicide. Positive findings could not be replicated and were confounded by variables such as season, day of the week, weather and holidays.

No increase in psychiatric admission for adults

• Looking at 100 psychiatric admissions of developmentally disabled adults over a 4-year period, Gorvin and Roberts found that the relation with the full moon was an example of an “illusory correlation.” The full moon accounted for only 0.007% of variance, and thus the results were contrary to the lunar hypothesis.

• A 2019 review of nearly 18,000 medical records from different facilities found the same thing: no relationship between lunar cycles and the length of hospital stays or the number of inpatient admissions or discharges at psychiatric facilities.

No increase in psychiatric contacts in Italy.

• In 1997 Amaddeo and colleagues studied the number of all psychiatric contacts in the province of Verona over a 10-year period and their correlation to the synodic cycle. They tested the null hypothesis versus a sinusoidal distribution of contacts according to lunar phases and found no relation between the 4 intervals of the synodic month and frequency of contact. Similarly, no significant results were found by setting the expected surge in consultation at 1–3 days after the full moon.

Increase in rapid switching in Bipolar Disorder

• Researchers have found that those with bipolar disorder may be affected by changes in the lunar cycle. Specifically, a 2018 study examined 17 people whose bipolar disorder tended to switch rapidly from depression to mania.

No increased aggression in Australia.

• The relationship between the full moon and aggression was studied in 5 inpatient settings in Sydney, Australia. The “Morrison's hierarchy of violence and aggression” was used as a behavioural scale, and the lunar phases were defined with Poisson regression over 105 weeks. No relation was found, as the trend of increasing violence across the 4 phases did not reach significance. There was also no modification of patterns when weekends and public holidays were taken into account. The investigators concluded that the severity of violent behaviour did not vary with the phases of the moon.

A small increase in general practice consultant rates.

• Neal and Colledge demonstrated a real, if small, rise in general practice consultations 6 days after the full moon. This delay is presumably due to delays between the onset of moon-related problems and behaviours, and accessing the GP.

Small changes in physical activity, sleep duration and metabolic health in kids.

• This Danish study looked at 24-hour accelerometer recordings of activity and sleep as well as measurements of cardiometabolic health.

• During the period around the full moon, children were

  • 5.0 and 3.2 min per day less active

  • Slept 2.4 and 4.1 min per night longer

  • Had 0.03 and 0.05 higher homeostatic model assessment of insulin resistance and 0.6 and 0.8 mmHg higher mean arterial blood pressure compared with days around half moon and new moon, respectively (all P ≤ 0.02).

  • Ghrelin was lower and leptin was higher during the period around the full moon compared with days around half moon

Decreased delta activity in sleep, subjective quality of sleep and lower melatonin levels.

• This study found that around the full moon, electroencephalogram (EEG) delta activity during NREM sleep, an indicator of deep sleep, decreased by 30%, time to fall asleep increased by 5 min, and EEG-assessed total sleep duration was reduced by 20 min. These changes were associated with a decrease in subjective sleep quality and diminished endogenous melatonin levels. Also, this 2021 study found that people fell asleep later and slept less overall on the nights before the full moon.

References

Bad Moon Rising - CMAJ

Lunacy and the Full Moon - Scientific American

The mood-altering power of the Moon - BBC

Lunar Effect - Wikipedia