The birthday effect (sometimes called the birthday blues, especially when referring specifically to
suicide) is a statistical phenomenon where an individual's likelihood of death appears to increase on or close to their birthday. The birthday effect has been seen in studies of general populations in England and Wales,
Switzerland,
Ukraine,
and the United States,
as well as in smaller populations such as
Major League Baseball
Major League Baseball (MLB) is a professional baseball organization and the oldest major professional sports league in the world. MLB is composed of 30 total teams, divided equally between the National League (NL) and the American League (AL), ...
players.
Studies do not consistently show this effect; some studies find that men's and women's mortality rates diverge in the run-up to the birthday,
while others find no
significant gender effect.
Suggested mechanisms for the effect include alcohol consumption,
psychological stress relating to the birthday, increased suicide risk, terminally ill patients attempting to hold on until their birthday, an increased
mortality salience
Mortality salience is the awareness by individuals that their death is inevitable.
The term derives from terror management theory, which proposes that mortality salience causes existential anxiety that may be buffered by an individual's cultural ...
, or a physiological cycle that causes the body to weaken annually. It has also been suggested that it may be a statistical artifact, perhaps as a result of anomalies in reporting, but the birthday effect has also been seen in studies that control for known reporting anomalies.
Studies
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With the introduction of statistical software that can process large datasets easily, a number of state- or country-wide studies have been carried out to investigate whether birthdays have any effect on mortality. The first large-scale study used the records of 2,745,149 Californians who died between 1969 and 1990. After correcting for confounding factors such as
seasonality
In time series data, seasonality is the presence of variations that occur at specific regular intervals less than a year, such as weekly, monthly, or quarterly. Seasonality may be caused by various factors, such as weather, vacation, and holidays a ...
in deaths, elective surgery, and people born on
February 29
February 29, also known as leap day or leap year day, is a date added to leap years. A leap day is added in various solar calendars (calendars based on the Earth's revolution around the Sun), including the Gregorian calendar standard in mos ...
, there was a significant increase in deaths in the week before the individual's birthday for men, and in the week after the birthday for women – in both cases, mortality did not peak on the birthday, but close to it. This effect was consistent across age and race cohorts.
A similar study among 12,275,033 Swiss found the highest mortality on the actual birthday (17% greater than the expected value), and the effect was largest for those over 80;
another study on Swiss data found a 13.8% excess and was able to link this to specific causes:
heart attack
A myocardial infarction (MI), commonly known as a heart attack, occurs when blood flow decreases or stops to the coronary artery of the heart, causing damage to the heart muscle. The most common symptom is chest pain or discomfort which ma ...
and
stroke (predominant in women) and suicides and accidents (predominant in men), as well as an increase in cancer deaths.
Among 25 million Americans who died between 1998 and 2011, 6.7% more people than expected die on their birthday, and the effect was most pronounced at weekends and among the young – among 20 to 29 year olds, the excess was over 25%.
An even greater excess was found in the population of
Kyiv
Kyiv, also spelled Kiev, is the capital and most populous city of Ukraine. It is in north-central Ukraine along the Dnieper River. As of 1 January 2021, its population was 2,962,180, making Kyiv the seventh-most populous city in Europe.
Kyi ...
, where between 1990 and 2000 there were 44.4% more deaths than expected among men on their birthdays and 36.2% more than expected among women.
Smaller biographical studies have also shown a birthday effect within subpopulations, such as among Major League Baseball (MLB) players
and people with entries in the ''Encyclopedia of American History''.
Focusing on suicide deaths alone, large studies have found evidence for a peak in suicides on or just after a birthday in
Denmark
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, song_type = National and royal anthem
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and
Hungary
Hungary ( hu, Magyarország ) is a landlocked country in Central Europe. Spanning of the Pannonian Basin, Carpathian Basin, it is bordered by Slovakia to the north, Ukraine to the northeast, Romania to the east and southeast, Serbia to the ...
,
but not in
Bavaria
Bavaria ( ; ), officially the Free State of Bavaria (german: Freistaat Bayern, link=no ), is a state in the south-east of Germany. With an area of , Bavaria is the largest German state by land area, comprising roughly a fifth of the total lan ...
or
Taiwan
Taiwan, officially the Republic of China (ROC), is a country in East Asia, at the junction of the East and South China Seas in the northwestern Pacific Ocean, with the People's Republic of China (PRC) to the northwest, Japan to the nort ...
.
However, other studies have not found such a correlation. A study using the populations of Denmark and
Austria
Austria, , bar, Östareich officially the Republic of Austria, is a country in the southern part of Central Europe, lying in the Eastern Alps. It is a federation of nine states, one of which is the capital, Vienna, the most populous ...
(a total of 2,052,680 deaths over the time period) found that although people's life span tended to correlate with their month of birth, there was no consistent birthday effect, and people born in autumn or winter were more likely to die in the months further from their birthday.
A study of all cancer deaths in Germany from 1995 to 2009 found no evidence of a birthday effect, although it did find a related Christmas effect.
A small study by
Leonard Zusne found birthday effects among both male and female cohorts, where women were more likely to die immediately before a birthday and men more likely to die immediately after, but that when averaged together there was no birthday effect among the population as a whole.
The same was found for a study of mortality data in England and Wales, where there was a statistically significant birthday effect among each subgroup (men and women; never married, married, divorced and widowed) but
it was not seen in the population as a whole.
Possible explanations
Alcohol
Birthday celebrations are often associated with large increases in alcohol consumption.
Binge drinking can
increase an individual's risk of death through
alcohol intoxication, accidents and
drunk driving, as well as by exacerbating existing conditions and increasing suicide risk.
In the US where the legal minimum drinking age is 21, there is a very large mortality rate excess on the 21st birthday and the day immediately following, almost entirely attributable to an increase in accidents.
Psychosomatic and psychological
Two mutually contradictory explanations have been put forward that rely on
psychosomatic effects. On the one hand, a birthday provides a fixed date to focus on, allowing the terminally ill to hold on until the day itself. On the other hand, a birthday also reminds the individual of mortality and offers an occasion to look back on life.
According to the
terror management theory, this causes stress which can accelerate death. The uneven mortality rate distribution between men and women, and between more and less successful baseball players, suggests that both may play a role in the birthday effect: people who have focused on the
public sphere
The public sphere (german: Öffentlichkeit) is an area in social life where individuals can come together to freely discuss and identify societal problems, and through that discussion influence political action. A "Public" is "of or concerning the ...
of life (for example,
career
The career is an individual's metaphorical "journey" through learning, work and other aspects of life. There are a number of ways to define career and the term is used in a variety of ways.
Definitions
The ''Oxford English Dictionary'' defi ...
-driven people or professional athletes) might be reminded that their glory days have passed, while those who lived more in the
private sphere The private sphere is the complement or opposite to the public sphere. The private sphere is a certain sector of societal life in which an individual enjoys a degree of authority, unhampered by interventions from governmental or other institutions. ...
(such as stay-at-home parents and amateur sports players) are more aware of what they will lose in death and try to hold on.
Related is the "broken promise effect", whereby a person suffering
suicidal ideation will wait until a birthday or other significant event to see whether their circumstances will improve.
The psychosomatic/psychological model would also explain the similar increase in cancer deaths around holidays such as
Christmas
Christmas is an annual festival commemorating the birth of Jesus Christ, observed primarily on December 25 as a religious and cultural celebration among billions of people around the world. A feast central to the Christian liturgical year ...
,
and is supported by the fact that such phenomena appear to be dependent on culture – there is a
Passover
Passover, also called Pesach (; ), is a major Jewish holiday that celebrates the Biblical story of the Israelites escape from slavery in Egypt, which occurs on the 15th day of the Hebrew month of Nisan, the first month of Aviv, or spring. ...
effect among the Jewish community (which moves
with the festival), and a
Mid-Autumn Festival effect among the Chinese.
Physiological
It has been suggested that, like the 24-hour
circadian rhythm, the body also has a yearly "circannual"
biological rhythm
Biological rhythms are repetitive biological processes. Some types of biological rhythms have been described as biological clocks. They can range in frequency from microseconds to less than one repetitive event per decade. Biological rhythms are st ...
. Vaiserman et al. have suggested that the climatic conditions at birth act as a
zeitgeber
A zeitgeber () is any external or environmental cue that entrains or synchronizes an organism's biological rhythms, usually naturally occurring and serving to entrain to the Earth's 24-hour light/dark and 12-month cycles.
History
The term ' (; ) ...
that triggers internal stress and increases the chance of death.
Statistical
It is possible when processing
death certificate
A death certificate is either a legal document issued by a medical practitioner which states when a person died, or a document issued by a government civil registration office, that declares the date, location and cause of a person's death, as ...
s to confuse the date of birth and date of death fields, which would increase the apparent number of certificates in which these coincide.
Additionally, where the exact date is not known, the 1st and 15th of the month are often used as placeholders.
These will cause an excess of births and deaths recorded on these dates. However studies also find changes in the mortality rate in the days immediately before and after, which are unlikely to be caused by data processing anomalies, suggesting that statistical artifacts alone cannot explain the birthday effect.
References
{{death
Birthdays
Death
Medical statistics
Suicide
Unexplained phenomena