Influence of seasonal birth in humans

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Interactive heat map of ratios of births on each day of the year to the average, in USA (top) and England and Wales (bottom)
[Legend and sources] Most common birthdays.svg
Interactive heat map of ratios of births on each day of the year to the average, in USA (top) and England and Wales (bottom)
[Legend and sources]

Seasonal variation in human birth rate has been found to be a nearly universal phenomenon. [1] Also, birth seasonality has been found to be correlated with certain physiological and psychological traits of humans and animals [2] [3] and type I diabetes. [4] Evidence for seasonality in humans is limited. [5]

Contents

Description

A ranking based on how many babies were born in the United States on that date between 1973 and 1999 Graphic birthday rank USA.svg
A ranking based on how many babies were born in the United States on that date between 1973 and 1999

Findings

Influence on medical conditions

The season in which babies are born can have an effect on their future risk of developing neurological disorders like seasonal affective disorder, bipolar depression, and schizophrenia; [2] [3] as well as type I diabetes. [4] Research has shown that the season of a baby’s birth can have an effect on whether or not they will become a heavy smoker. Although the aspects of this effect differ by sex, the effect exists across both of them. [6]

Large-scale population analytic studies

Recently, large-scale population analytics have allowed for the exploration of birth month/season hypotheses among large cohorts of people. One study used 1.7 million patients from Columbia University in New York City (NYC) to confirm associations between neurological conditions, respiratory condition and reproductive conditions with birth month. [7] In addition, they uncovered an association between cardiovascular diseases and birth month. [7] This was subsequently confirmed in a separate study, also using data from NYC. [8] Researchers also explored mechanisms correlated with birth season in a large population study including data from 10.5 million patients, from three countries (US, South Korea, and Taiwan) and six study sites. [9] They found correlations between relative age and school cutoff periods. And that first trimester exposure to fine air particulates increased the risk of atrial fibrillation later in life. [9]

As a factor in academic development

There is evidence that suggests that children born earlier in an academic year gain an advantage over their later-born classmates:

"In Britain the academic year begins in September, and there may be almost a year's chronological age difference between the eldest (September birthday) and youngest (August birthday) children in the same class. There is evidence that, in this context, children born in the autumn term (September to December birthdays) perform better academically, relative to their class peers, than those born in the spring term (January to April birthdays), who in turn outperform those born in the summer term (May to August birthdays)." [10]

As a suicide risk factor

Birth rates of people who later die by suicide show disproportionate excess for April, May and June compared with the other months. Overall, the risk of suicide increases by 17% for people born in the spring–early summer compared with those born in the autumn–early winter; this risk increase was larger for women (29.6%) than for men (13.7%). [11]

Research works in Sweden show that those who preferred suicide by hanging rather than poisoning or petrol gases were significantly more likely to be born during February–April. Maximum of the month-of-birth curve for preferring hanging was for March–April and the minimum was for September–October. [12]

However, other studies have shown that there is no effect of season of birth on psychological disorders, such as depression and anxiety. [13]

Related Research Articles

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<span class="mw-page-title-main">Bipolar disorder</span> Mental disorder that causes periods of depression and abnormally elevated mood

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<span class="mw-page-title-main">Major depressive disorder</span> Mood disorder

Major depressive disorder (MDD), also known as clinical depression, is a mental disorder characterized by at least two weeks of pervasive low mood, low self-esteem, and loss of interest or pleasure in normally enjoyable activities. Introduced by a group of US clinicians in the mid-1970s, the term was adopted by the American Psychiatric Association for this symptom cluster under mood disorders in the 1980 version of the Diagnostic and Statistical Manual of Mental Disorders (DSM-III), and has become widely used since. The disorder causes the second-most years lived with disability, after lower back pain.

<span class="mw-page-title-main">Mood disorder</span> Mental disorder affecting the mood of an individual, over a long period of time

A mood disorder, also known as an affective disorder, is any of a group of conditions of mental and behavioral disorder where the main underlying characteristic is a disturbance in the person's mood. The classification is in the Diagnostic and Statistical Manual of Mental Disorders (DSM) and International Classification of Diseases (ICD).

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The birthday effect 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 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, 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.

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<span class="mw-page-title-main">Selective serotonin reuptake inhibitor</span> Class of antidepressant medication

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<span class="mw-page-title-main">Differential diagnoses of depression</span> Differential diagnoses

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Research on seasonal effects on suicide rates suggests that the prevalence of suicide is greatest during the late spring and early summer months, despite the common belief that suicide rates peak during the cold and dark months of the winter season.

<span class="mw-page-title-main">Relative age effect</span> Statistical bias

The term relative age effect (RAE), also known as birthdate effect or birth date effect, is used to describe a bias, evident in the upper echelons of youth sport and academia, where participation is higher amongst those born earlier in the relevant selection period than would be expected from the distribution of births. The selection period is usually the calendar year, the academic year or the sporting season.

References

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