
The lunar effect is a purported correlation between specific stages of the roughly 29.5-day
lunar cycle and behavior and physiological changes in living beings on Earth, including humans. A considerable number of studies have examined the effect on humans. By the late 1980s, there were at least 40 published studies on the purported lunar-lunacy connection,
and at least 20 published studies on the purported lunar-birthrate connection.
Literature reviews and metanalyses have found no correlation between the lunar cycle and human biology or behavior.
In cases such as the approximately monthly cycle of
menstruation
Menstruation (also known as a period, among other colloquial terms) is the regular discharge of blood and Mucous membrane, mucosal tissue from the endometrium, inner lining of the uterus through the vagina. The menstrual cycle is characterized ...
in humans (but not other mammals), the coincidence in timing reflects no known lunar influence. The widespread and persistent beliefs about the influence of the Moon may depend on
illusory correlation
In psychology
Psychology is the scientific study of mind and behavior. Its subject matter includes the behavior of humans and nonhumans, both consciousness, conscious and Unconscious mind, unconscious phenomena, and mental processes such ...
– the perception of an association that does not in fact exist.
In a number of marine animals, there is stronger evidence for the effects of lunar cycles. Observed effects relating to
reproductive synchrony may depend on external cues relating to the presence or amount of
moonlight. Corals contain light-sensitive
cryptochromes, proteins that are sensitive to different levels of light. Coral species such as ''
Dipsastraea speciosa'' tend to synchronize spawning in the evening or night, around the last quarter moon of the lunar cycle. In ''Dipsastraea speciosa'', a period of darkness between sunset and moonrise appears to be a trigger for synchronized spawning. Another marine animal, the bristle worm ''
Platynereis dumerilii'', spawns a few days after a full moon. It contains a protein with light-absorbing flavin structures that differentially detect moonlight and sunlight. It is used as a model for studying the biological mechanisms of marine lunar cycles.
Contexts
Claims of a lunar connection have appeared in the following contexts:
Fertility
It is widely believed that the Moon has a relationship with
fertility
Fertility in colloquial terms refers the ability to have offspring. In demographic contexts, fertility refers to the actual production of offspring, rather than the physical capability to reproduce, which is termed fecundity. The fertility rate ...
due to the corresponding human
menstrual cycle
The menstrual cycle is a series of natural changes in hormone production and the structures of the uterus and ovaries of the female reproductive system that makes pregnancy possible. The ovarian cycle controls the production and release of eg ...
, which averages 28 days.
However, no connection between lunar rhythms and menstrual onset has been conclusively shown to exist, and the similarity in length between the two cycles is most likely coincidental.
Birth rate
Multiple studies have found no connection between
birth rate and lunar phases. A 1957 analysis of 9,551 births in
Danville, Pennsylvania, found no correlation between birth rate and the phase of the Moon.
Records of 11,961 live births and 8,142 natural births (not induced by drugs or cesarean section) over a 4-year period (1974–1978) at the
UCLA
The University of California, Los Angeles (UCLA) is a public land-grant research university in Los Angeles, California, United States. Its academic roots were established in 1881 as a normal school then known as the southern branch of the C ...
hospital did not correlate in any way with the cycle of lunar phases.
Analysis of 3,706 spontaneous births (excluding births resulting from induced labor) in 1994 showed no correlation with lunar phase.
The distribution of 167,956 spontaneous vaginal deliveries, at 37 to 40 weeks gestation, in
Phoenix, Arizona
Phoenix ( ) is the List of capitals in the United States, capital and List of cities and towns in Arizona#List of cities and towns, most populous city of the U.S. state of Arizona. With over 1.6 million residents at the 2020 census, it is the ...
, between 1995 and 2000, showed no relationship with lunar phase.
Analysis of 564,039 births (1997 to 2001) in
North Carolina
North Carolina ( ) is a U.S. state, state in the Southeastern United States, Southeastern region of the United States. It is bordered by Virginia to the north, the Atlantic Ocean to the east, South Carolina to the south, Georgia (U.S. stat ...
showed no predictable influence of the lunar cycle on deliveries or complications.
Analysis of 6,725 deliveries (2000 to 2006) in
Hannover
Hanover ( ; ; ) is the capital and largest city of the States of Germany, German state of Lower Saxony. Its population of 535,932 (2021) makes it the List of cities in Germany by population, 13th-largest city in Germany as well as the fourth-l ...
revealed no significant correlation of birth rate to lunar phases.
A 2001 analysis of 70,000,000 birth records from the
National Center for Health Statistics revealed no correlation between birth rate and lunar phase.
An extensive review of 21 studies from seven different countries showed that the majority of studies reported no relationship to lunar phase, and that the positive studies were inconsistent with each other.
A review of six additional studies from five different countries similarly showed no evidence of relationship between birth rate and lunar phase.
In 2021, an analysis of 38.7 million births in France over 50 years, with a detailed correction for birth variations linked to holidays, and robust statistical methods to avoid false detections linked to multiple tests, found a very small (+0.4%) but statistically significant surplus of births on the full moon day, and to a lesser extent the following day. The probability of this excess being due to chance is very low, of the order of one chance in 100,000 (p-value = 1.5 x 10-5). The belief that there is a large surplus of births on full moon days is incorrect, and it is completely impossible for an observer to detect the small increase of +0.4% in a maternity hospital, even on a long time scale.
Blood loss
It is sometimes claimed that surgeons used to refuse to operate during the full Moon because of the increased risk of death of the patient through blood loss. One team, in
Barcelona
Barcelona ( ; ; ) is a city on the northeastern coast of Spain. It is the capital and largest city of the autonomous community of Catalonia, as well as the second-most populous municipality of Spain. With a population of 1.6 million within c ...
,
Spain
Spain, or the Kingdom of Spain, is a country in Southern Europe, Southern and Western Europe with territories in North Africa. Featuring the Punta de Tarifa, southernmost point of continental Europe, it is the largest country in Southern Eur ...
, reported a weak correlation between lunar phase and hospital admissions due to
gastrointestinal bleeding, but only when comparing full Moon days to all non-full Moon days lumped together.
This methodology has been criticized, and the statistical significance of the results disappears if one compares day 29 of the lunar cycle (full Moon) to days 9, 12, 13, or 27 of the lunar cycle, which all have an almost equal number of hospital admissions. The Spanish team acknowledged that the wide variation in the number of admissions throughout the lunar cycle limited the interpretation of the results.
In October 2009, British politician
David Tredinnick asserted that during a full Moon "
rgeons will not operate because blood clotting is not effective and the police have to put more people on the street.". A spokesman for the
Royal College of Surgeons
The Royal College of Surgeons is an ancient college (a form of corporation) established in England to regulate the activity of surgeons. Derivative organisations survive in many present and former members of the Commonwealth. These organisations ...
said they would "laugh their heads off" at the suggestion they could not operate on the full Moon.
Human behavior
Epilepsy
A study into epilepsy found a significant negative correlation between the mean number of epileptic seizures per day and the fraction of the Moon that is illuminated, but the effect resulted from the overall brightness of the night, rather than from the moon phase per se.
Law and order
Senior police officers in
Brighton
Brighton ( ) is a seaside resort in the city status in the United Kingdom, city of Brighton and Hove, East Sussex, England, south of London.
Archaeological evidence of settlement in the area dates back to the Bronze Age Britain, Bronze Age, R ...
, UK, announced in June 2007 that they were planning to deploy more officers over the summer to counter trouble they believe is linked to the lunar cycle. This followed research by the
Sussex Police force that concluded there was a rise in violent crime when the Moon was full. A spokeswoman for the police force said "research carried out by us has shown a correlation between violent incidents and full moons". A police officer responsible for the research told the BBC that "From my experience of 19 years of being a police officer, undoubtedly on full moons we do seem to get people with sort of strange behavior – more fractious, argumentative."
Police in
Ohio
Ohio ( ) is a U.S. state, state in the Midwestern United States, Midwestern region of the United States. It borders Lake Erie to the north, Pennsylvania to the east, West Virginia to the southeast, Kentucky to the southwest, Indiana to the ...
and
Kentucky
Kentucky (, ), officially the Commonwealth of Kentucky, is a landlocked U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders Illinois, Indiana, and Ohio to the north, West Virginia to the ...
have blamed temporary rises in crime on the full Moon.
In January 2008,
New Zealand
New Zealand () is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and List of islands of New Zealand, over 600 smaller islands. It is the List of isla ...
's Justice Minister
Annette King suggested that a spate of stabbings in the country could have been caused by the lunar cycle.
A reported correlation between Moon phase and the number of homicides in
Miami-Dade County
Miami-Dade County () is a county located in the southeastern part of the U.S. state of Florida. The county had a population of 2,701,767 as of the 2020 census, making it the most populous county in Florida and the seventh-most-populous coun ...
was found, through later analysis, not to be supported by the data and to have been the result of inappropriate and misleading statistical procedures.
[. Reprinted in ''The Hundredth Monkey – and other paradigms of the paranormal'', edited by Kendrick Frazier, Prometheus Books. Revised and updated in ''The Outer Edge: Classic Investigations of the Paranormal'', edited by Joe Nickell, Barry Karr, and Tom Genoni, 1996, CSICOP.]
Motorcycle fatalities
A study of 13,029 motorcyclists killed in nighttime crashes found that there were 5.3% more fatalities on nights with a full moon compared to other nights. The authors speculate that the increase might be due to visual distractions created by the moon, especially when it is near the horizon and appears abruptly between trees, around turns, etc.
Stock market
Several studies have argued that the stock market's average returns are much higher during the half of the month closest to the new moon than the half closest to the full moon. The reasons for this have not been studied, but the authors suggest this may be due to lunar influences on mood.
Another study has found contradictory results and questioned these claims.
Meta-analyses
A meta-analysis of thirty-seven studies that examined relationships between the Moon's four phases and human behavior revealed no significant correlation. The authors found that, of twenty-three studies that had claimed to show correlation, nearly half contained at least one
statistical
Statistics (from German language, German: ', "description of a State (polity), state, a country") is the discipline that concerns the collection, organization, analysis, interpretation, and presentation of data. In applying statistics to a s ...
error.
Similarly, in a review of twenty studies examining correlations between Moon phase and suicides, most of the twenty studies found no correlation, and the ones that did report positive results were inconsistent with each other.
A 1978 review of the literature also found that lunar phases and human behavior are not related.
Sleep quality
A 2013 study by Christian Cajochen and collaborators at the
University of Basel suggested a correlation between the full Moon and human sleep quality.
However, the validity of these results may be limited because of a relatively small (n=33) sample size and inappropriate controls for age and sex.
A 2014 study with larger sample sizes (n1=366, n2=29, n3=870) and better experimental controls found no effect of the lunar phase on sleep quality metrics.
A 2015 study of 795 children found a three-minute ''increase'' in sleep duration near the full moon,
but a 2016 study of 5,812 children found a five-minute ''decrease'' in sleep duration near the full moon.
No other modification in activity behaviors were reported,
and the lead scientist concluded: "Our study provides compelling evidence that the moon does not seem to influence people's behavior."
A study published in 2021 by researchers from the
University of Washington
The University of Washington (UW and informally U-Dub or U Dub) is a public research university in Seattle, Washington, United States. Founded in 1861, the University of Washington is one of the oldest universities on the West Coast of the Uni ...
,
Yale University
Yale University is a Private university, private Ivy League research university in New Haven, Connecticut, United States. Founded in 1701, Yale is the List of Colonial Colleges, third-oldest institution of higher education in the United Stat ...
, and the
National University of Quilmes showed a correlation between lunar cycles and sleep cycles. During the days preceding a full moon, people went to bed later and slept for shorter periods (in some cases with differences of up to 90 minutes), even in locations with full access to electric light. Finally, a Swedish study including one-night at-home sleep recordings from 492 women and 360 men found that men whose sleep was recorded during nights in the waxing period of the lunar cycle exhibited lower sleep efficiency and increased time awake after sleep onset compared to men whose sleep was measured during nights in the waning period. In contrast, the sleep of women remained largely unaffected by the lunar cycle. These results were robust to adjustment for chronic sleep problems and obstructive sleep apnea severity.
As for how the belief started in the first place, a 1999 study conjectures that the alleged connection of moon to lunacy might be a ‘cultural fossil’ from a time before the advent of outdoor lighting, when the bright light of the full moon might have induced sleep deprivation in people living outside, thereby triggering erratic behaviour in predisposed people with mental conditions such as bipolar disorder.
In animals
Corals contain light-sensitive
cryptochromes, proteins that are sensitive to different levels of light.
Spawning of coral ''
Platygyra lamellina'' occurs at night during the summer on a date determined by the
phase of the Moon; in the
Red Sea
The Red Sea is a sea inlet of the Indian Ocean, lying between Africa and Asia. Its connection to the ocean is in the south, through the Bab-el-Mandeb Strait and the Gulf of Aden. To its north lie the Sinai Peninsula, the Gulf of Aqaba, and th ...
, this is the three- to five-day period around the
new Moon in July and the similar period in August. ''
Acropora'' coral time their simultaneous release of sperm and eggs to just one or two days a year, after sundown with a full moon.
''
Dipsastraea speciosa'' tends to synchronize spawning in the evening or night, around the last quarter moon of the lunar cycle.
Another marine animal, the bristle worm ''
Platynereis dumerilii'', also spawns a few days after a full moon. It is used as a model for studying cryptochromes and photoreduction in proteins. The L-Cry protein can distinguish between sunlight and moonlight through the differential activity of two protein strands that contain light-absorbing structures called flavins. Another molecule, called r-Opsin, may act as a moonrise sensor. Exactly how different biological signals are transmitted within the worm is not yet known.
Correlation between hormonal changes in the
testis
A testicle or testis ( testes) is the gonad in all male bilaterians, including humans, and is Homology (biology), homologous to the ovary in females. Its primary functions are the production of sperm and the secretion of Androgen, androgens, p ...
and lunar periodicity was found in
streamlined spinefoot (a type of fish), which spawns synchronously around the last Moon quarter.
In
orange-spotted spinefoot, lunar phases affect the levels of
melatonin in the blood.
California grunion fish have an unusual mating and spawning ritual during the spring and summer months. The egg laying takes place on four consecutive nights, beginning on the nights of the full and new Moons, when tides are highest. This well understood reproductive strategy is related to tides, which are highest when the Sun, Earth, and Moon are aligned, i.e., at new Moon or full Moon.
In insects, the lunar cycle may affect hormonal changes.
The body weight of
honeybees peaks during
new Moon.
The
midge ''
Clunio marinus'' has a biological clock synchronized with the Moon.
Evidence for lunar effect in reptiles, birds and mammals is scant,
but among reptiles
marine iguanas (which live in the
Galápagos Islands
The Galápagos Islands () are an archipelago of volcanic islands in the Eastern Pacific, located around the equator, west of the mainland of South America. They form the Galápagos Province of the Republic of Ecuador, with a population of sli ...
) time their trips to the sea in order to arrive at low tide.
A relationship between the Moon and the birth rate of cows was reported in a 2016 study.
In 2000, a retrospective study in the
United Kingdom
The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Northwestern Europe, off the coast of European mainland, the continental mainland. It comprises England, Scotlan ...
reported an association between the full moon and significant increases in animal bites to humans. The study reported that patients presenting to the
A&E with injuries stemming from bites from an animal rose significantly at the time of a full moon in the period 1997–1999. The study concluded that animals have an increased inclination to bite a human during a full moon period. It did not address the question of how humans came into contact with the animals, and whether this was more likely to happen during the full moon.
In plants
Serious doubts have been raised about the claim that a species of ''
Ephedra'' synchronizes its pollination peak to the full moon in July. Reviewers conclude that more research is needed to answer this question.
See also
*
List of topics characterized as pseudoscience
*
Astrology
Astrology is a range of Divination, divinatory practices, recognized as pseudoscientific since the 18th century, that propose that information about human affairs and terrestrial events may be discerned by studying the apparent positions ...
*
Human menstrual cycle
*
Menstrual synchrony
*
Reproductive synchrony
*
Solunar theory
*
Tide
Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another.
Tide tables ...
References
Bibliography
* Abell, George (1979). Review of the book ''The Alleged Lunar Effect'' by Arnold Lieber, ''
Skeptical Inquirer'', Spring 1979, 68–73. Reprinted in ''Science Confronts the Paranormal'', edited by
Kendrick Frazier,
Prometheus Books, .
* Abell, George and Barry Singer (1981). ''Science and the Paranormal – probing the existence of the supernatural'',
Charles Scribner's Sons, chapter 5, .
*
Berman, Bob (2003). Fooled by the Full Moon – Scientists search for the sober truth behind some loony ideas, ''
Discover'', September 2003, page 30.
* Caton, Dan (2001). Natality and the Moon Revisited: Do Birth Rates Depend on the Phase of the Moon?, ''
Bulletin of the American Astronomical Society'', Vol 33, No. 4, 2001, p. 1371
A summary of the results of the paper.*
*
*
*
* Sanduleak, Nicholas (1985). The Moon is Acquitted of Murder in Cleveland, ''Skeptical Inquirer'', Spring 1985, 236–242. Reprinted in ''Science Confronts the Paranormal'', edited by
Kendrick Frazier, Prometheus Books, .
*
External links
The Skeptic's Dictionary on the lunar effect*
*
*
{{Use dmy dates, date=September 2018
Moon myths
Pseudoscience
Chronobiology
Astrology
Periodic phenomena