TL;DR: Crime, suicide, and hospital admissions: pooled analyses show near-zero correlation with lunar phase, and births are the same. Sleep is the one area where evidence remains debated: two small lab studies reported shorter sleep around the full moon, but a larger dataset could not reproduce that result, and the group that failed to reproduce it even warned about publication bias. The most plausible point is moonlight: where there is no electric lighting, bright moonlight in the early evening keeps people up later, and that is an effect of light, not of gravity.
Does the full moon make people behave strangely: crime, birth rates and sleep under the lens of data
Does the full moon really make people behave strangely?
With behaviour and birth rates, the short answer is no: large reviews have found no effect of the lunar phase. With sleep, the answer is still debated, and most of the difference lies in light, not in gravitational pull. The belief that "a full moon brings strange happenings" has very deep cultural roots, but when put to the test with data it does not hold up in most areas.
What does a meta-analysis of 37 studies on lunar phase and behaviour say?
James Rotton and I. W. Kelly published in 1985 in Psychological Bulletin a meta-analysis of 37 studies on the relationship between lunar phase and human behaviour, and the correlation found was close to zero. This is the strongest level of evidence on this topic: not a single study, but a synthesis of many independent studies, large enough that if a real effect existed it would have to show up. The authors' summary states the scope clearly: the studies gathered together mostly revolved around crime, behavioural disorders and psychiatric emergency calls, and the scattered positive results were explained by the group as methodological error rather than as an effect of the moon.
The article you are reading here presents only behavioural and population studies. It offers no advice about sleep or health, and does not aim to tell anyone to change their sleep habits or health care according to the lunar phase.
The scope needs to be stated clearly: this meta-analysis gathered studies from many Western countries, mostly hospital, police and psychiatric records. It says nothing about Vietnamese people, simply because there is no Vietnamese data in it. A result "close to zero" also does not mean that every individual study was zero: there are still isolated studies that found something, but when pooled together that something disappears, exactly as random effects work.
Do birth rates rise on the night of the full moon?
I. W. Kelly and R. Martens published in 1994 in Psychological Reports a review of lunar phase and birth rates, and concluded that no study showed the lunar cycle affecting birth rates. This is level A: stated plainly, with no hedging needed. This group added six studies from five countries to 21 earlier studies, according to their abstract, and across the whole review not a single study supported the folk notion that the lunar cycle makes birth rates fluctuate.
Thomas K. Bauer and colleagues published in 2013 in Economics & Human Biology a study on birth data in Germany from 1920 to 1989, and also found no effect of the lunar cycle on birth rates. The strength of this study is its time scale: nearly seven decades of data, long enough that if the lunar cycle had an effect it would have to appear somewhere. That it does not appear is a very strong negative result. Interestingly, this group also examined sunspot numbers and recorded a very small positive effect, declining over time, but that is a matter of sunspots, not of the lunar cycle.
For Vietnamese people, there is no similar study. There is no basis to say whether the lunar cycle does or does not affect birth rates in Vietnam, simply because no one has done the research.
Sleep under the full moon: what does the evidence say?
This is the one place where the story is more complicated.
Christian Cajochen and colleagues published in 2013 in Current Biology a small study on people sleeping in a laboratory, and reported that sleep was shorter around the full moon. This is level B: an interesting result but not solidly replicated, and with a small sample size.
Michael Smith, Ilona Croy and Kerstin Persson Waye published in 2014 in Current Biology a report from a sleep laboratory in Sweden, recording shorter sleep and different cortical responses around the full moon. This is also level B: the result is still debated, and notably this paper was published in the same journal issue as the paper by Cordi and colleagues, which found no effect. The fact that two contradictory papers sit side by side in the same issue shows that researchers have not reached a settled conclusion on this matter.
Maren Cordi and colleagues published in 2014 in Current Biology an attempt to replicate that result on a larger dataset, and could not replicate it. Just as importantly, this group also raised the "file drawer" problem: studies that find an effect tend to get published, while studies that find nothing tend to be put in a drawer, unknown to anyone. The consequence is that isolated positive results get inflated in readers' eyes, because readers only see the tip of the iceberg.
Russell G. Foster and Till Roenneberg published in 2008 in Current Biology a review of human responses to geophysical cycles of day, year and moon, and concluded that daily and seasonal rhythms have solid evidence, while the lunar cycle is weak and contradictory. This is a useful way to frame the question: not all astronomical cycles are alike in their degree of influence. The daily rhythm is obvious, because sunlight governs it strongly. The lunar cycle is far fainter.
So where does it make sense?
Leandro Casiraghi and colleagues published in 2021 in Science Advances a study on three Toba/Qom communities in Formosa province, Argentina, with very different degrees of urbanisation. The main result: in the community with the least electric lighting, people went to bed later on nights with bright moonlight in the early evening, and slept less. This is level B: the result has not been replicated in other populations, but the mechanism is plausible and easy to understand.
The key point: that effect comes from light, not from gravitational pull. Moonlight is bright enough for the human eye to register, and in conditions with no other light source it can delay bedtime. When electric lighting is present, moonlight becomes negligible compared with artificial light. The Casiraghi group itself also measured that the level of light pollution in the urban Seattle area, where students typically live, is even higher than the full moonlight measured in the rural Toba/Qom area.
In other words: if you live in a city with streetlights, the hypothesis "the moon keeps me awake" holds up far less well than for someone living where there is no electricity.
Comparison table of the main studies
| Study | Data scope | Result |
|---|---|---|
| Rotton and Kelly 1985 | Meta-analysis of 37 studies on lunar phase and behaviour | Correlation close to zero |
| Kelly and Martens 1994 | Review of lunar phase and birth rates | No study showed an effect |
| Bauer and colleagues 2013 | Birth data in Germany 1920 to 1989 | Lunar cycle does not affect birth rates |
| Cajochen and colleagues 2013 | Small laboratory study | Shorter sleep around the full moon (level B) |
| Smith, Croy and Persson Waye 2014 | Sleep laboratory in Sweden | Shorter sleep and different cortical responses around the full moon (level B) |
| Cordi and colleagues 2014 | Larger dataset | Could not replicate the effect; warned of publication bias |
| Casiraghi and colleagues 2021 | Three Toba/Qom communities, Argentina | Where there is little electric light, bright moonlight makes people go to bed later (level B) |
| Foster and Roenneberg 2008 | Review of geophysical cycles | Daily and seasonal rhythms solid; lunar cycle weak and contradictory |
Why does the belief remain strong even though the data do not support it?
In folk belief in many places, people believe that the night of the full moon is when strange things are likely to happen, children have trouble sleeping, adults get irritable, and births are more likely to occur. This belief exists in many Western cultures, tied to the image of the "werewolf" and to the word "lunatic" in English.
There is a psychological mechanism that explains why this belief sustains itself even though the data do not support it. It is confirmation bias: people remember the full moon nights when something unusual happened, and forget the ordinary full moon nights. Add to that the fact that the full moon is an easily noticed, easily remembered event, easy to attach to a story, so it becomes a natural hook for memory to cling to.
A noteworthy point: if a belief makes people change their behaviour, and the behaviour changes the outcome, then the effect is real but arises from the belief, not from the moon. For example, if a community observes abstinences on the full moon day and goes to worship, then social behaviour on the full moon day differs from ordinary days, but it differs because people organise their lives that way, not because of the moon's gravitational pull. This is where precision is needed: do not call that "astrology getting it right", and do not deny the effect either. It is simply that the effect has a social origin, not an astronomical one.
Where the evidence is still missing
There is no Vietnamese data for any of the questions above. There is no study on social behaviour on the full moon day or the first day of the lunar month in Vietnamese belief, such as abstinences, going to worship, or community activities. Nor is there any study on birth rates in Vietnam by lunar phase. Therefore, every conclusion in this article applies only to the data scope stated: mainly North America, Europe and some communities in Argentina. It does not extend to Vietnamese people when there is no research on Vietnamese people.
The question "does the moon's gravitational pull have effects on sleep that are specific to the hour of the day" remains open. The Casiraghi group raised this hypothesis in their 2021 paper, but they themselves also acknowledged that observational research cannot establish causation, and that one cannot manipulate people's exposure to the moon's gravitational pull in order to test it.
Further reading
The article Full Moon: meaning in astrology and in life presents how astrology understands the full moon. The article you are reading here presents behavioural and population data. The two articles answer two different questions: one says what the astrological system conventionally holds, the other says what measurable data show.
