![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](http://upload.wikimedia.org/wikipedia/commons/b/b6/Most_common_birthdays.svg)
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]
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]
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]
 | The examples and perspective in this article may not represent a worldwide view of the subject.(July 2023) |
There is evidence that suggests that children born earlier in an academic year gain an advantage over their later-born classmates:
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]
Bipolar disorder, previously known as manic depression, is a mental disorder characterized by periods of depression and periods of abnormally elevated mood that each last from days to weeks. If the elevated mood is severe or associated with psychosis, it is called mania; if it is less severe and does not significantly affect functioning, it is called hypomania. During mania, an individual behaves or feels abnormally energetic, happy or irritable, and they often make impulsive decisions with little regard for the consequences. There is usually also a reduced need for sleep during manic phases. During periods of depression, the individual may experience crying and have a negative outlook on life and poor eye contact with others. The risk of suicide is high; over a period of 20 years, 6% of those with bipolar disorder died by suicide, while 30–40% engaged in self-harm. Other mental health issues, such as anxiety disorders and substance use disorders, are commonly associated with bipolar 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.
A mood disorder, also known as an affective disorder, is any of a group of conditions of mental and behavioral disorder where a disturbance in the person's mood is the main underlying feature. The classification is in the Diagnostic and Statistical Manual of Mental Disorders (DSM) and International Classification of Diseases (ICD).
Seasonal affective disorder (SAD) is a mood disorder subset in which people who typically have normal mental health throughout most of the year exhibit depressive symptoms at the same time each year. It is commonly, but not always, associated with the reductions or increases in total daily sunlight hours that occur during the summer or winter.
Isotretinoin, also known as 13-cis-retinoic acid and sold under the brand name Accutane among others, is a medication used to prevent certain skin cancers such as squamous-cell carcinoma and to treat skin diseases like harlequin-type ichthyosis, and lamellar ichthyosis, and severe cystic acne or moderate acne that is unresponsive to antibiotics. It is a retinoid, meaning it is related to vitamin A, and is found in small quantities naturally in the body. Its isomer, tretinoin, is also an acne drug.
Catechol-O-methyltransferase is one of several enzymes that degrade catecholamines, catecholestrogens, and various drugs and substances having a catechol structure. In humans, catechol-O-methyltransferase protein is encoded by the COMT gene. Two isoforms of COMT are produced: the soluble short form (S-COMT) and the membrane bound long form (MB-COMT). As the regulation of catecholamines is impaired in a number of medical conditions, several pharmaceutical drugs target COMT to alter its activity and therefore the availability of catecholamines. COMT was first discovered by the biochemist Julius Axelrod in 1957.
Light therapy, also called phototherapy or bright light therapy is the exposure to direct sunlight or artificial light at controlled wavelengths in order to treat a variety of medical disorders, including seasonal affective disorder (SAD), circadian rhythm sleep-wake disorders, cancers, and skin wound infections. Treating skin conditions such as neurodermatitis, psoriasis, acne vulgaris, and eczema with ultraviolet light is called ultraviolet light therapy.
Depression is a mental state of low mood and aversion to activity. It affects more than 280 million people of all ages. Depression affects a person's thoughts, behavior, feelings, and sense of well-being. Depressed people often experience loss of motivation or interest in, or reduced pleasure or joy from, experiences that would normally bring them pleasure or joy.
There are more than 700,000 estimated suicide deaths every year. Suicide affects every demographic, yet there are some populations that are more impacted than others. For example, among 15–29 year olds, suicide is much more prominent; this being the fourth leading cause of death within this age group.
Men's health is a state of complete physical, mental, and social well-being, as experienced by men, and not merely the absence of disease. Differences in men's health compared to women's can be attributed to biological factors, behavioural factors, and social factors.
The paternal age effect is the statistical relationship between the father's age at conception and biological effects on the child. Such effects can relate to birthweight, congenital disorders, life expectancy and psychological outcomes. A 2017 review found that while severe health effects are associated with higher paternal age, the total increase in problems caused by paternal age is low. Average paternal age at birth reached a low point between 1960 and 1980 in many countries and has been increasing since then, but has not reached historically unprecedented levels. The rise in paternal age is not seen as a major public health concern.
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.
Suicide is the act of intentionally causing one's own death. Mental disorders, physical disorders, and substance abuse are risk factors.
Selective serotonin reuptake inhibitors (SSRIs) are a class of drugs that are typically used as antidepressants in the treatment of major depressive disorder, anxiety disorders, and other psychological conditions.
Tobacco smoking during pregnancy causes many detrimental effects on health and reproduction, in addition to the general health effects of tobacco. A number of studies have shown that tobacco use is a significant factor in miscarriages among pregnant smokers, and that it contributes to a number of other threats to the health of the foetus.
Depression, one of the most commonly diagnosed psychiatric disorders, is being diagnosed in increasing numbers in various segments of the population worldwide. Depression in the United States alone affects 17.6 million Americans each year or 1 in 6 people. Depressed patients are at increased risk of type 2 diabetes, cardiovascular disease and suicide. Within the next twenty years depression is expected to become the second leading cause of disability worldwide and the leading cause in high-income nations, including the United States. In approximately 75% of suicides, the individuals had seen a physician within the prior year before their death, 45–66% within the prior month. About a third of those who died by suicide had contact with mental health services in the prior year, a fifth within the preceding month.
The July effect, sometimes referred to as the July phenomenon, is a perceived but scientifically unfounded increase in the risk of medical errors and surgical complications that occurs in association with the time of year in which United States medical school graduates begin residencies. A similar period in the United Kingdom is known as the killing season or, more specifically, Black Wednesday, referring to the first Wednesday in August when postgraduate trainees commence their rotations. In reality, this phenomenon has not been proven in the scientific literature. In fact, large-scale meta analysis, which has aggregated over 110 studies on this topic, has shown no evidence of a July effect on mortality, morbidity, or readmission.
Schizophrenia affects around 0.3–0.7% of the general population at some point in life, or 21 million people worldwide as of 2020. By using precise methods in its diagnosis and a large, representative population, schizophrenia seems to occur with relative consistency over time during the last half-century.
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.
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.