Season A season is a division of the year based on changes in weather, ecology, and the number of daylight hours in a given region. On Earth, seasons are the result of the axial parallelism of Earth's tilted orbit around the Sun. In temperate and pol ...

al variation in human

birth rate The birth rate for a given period is the total number of live human births per 1,000 population divided by the length of the period in years. The number of live births is normally taken from a universal registration system for births; populati ...

has been found to be a nearly universal phenomenon. Also, birth seasonality has been found to be correlated with certain physiological and psychological traits of humans and animals.

Description

Findings

Influence on medical conditions

The season in which babies are born can have a dramatic effect on their future risk relating to the development of conditions such as neurological disorders, including

seasonal affective disorder Seasonal affective disorder (SAD) is a mood disorder subset, in which people who have normal mental health throughout most of the year exhibit depressive symptoms at the same time each year. Common symptoms include sleeping too much, having li ...

bipolar depression Bipolar disorder, previously known as manic depression, is a mental disorder characterized by periods of depression and periods of abnormally elevated mood that last from days to weeks each. If the elevated mood is severe or associated with ...

schizophrenia Schizophrenia is a mental disorder characterized by continuous or relapsing episodes of psychosis. Major symptoms include hallucinations (typically hearing voices), delusions, and disorganized thinking. Other symptoms include social withdra ...

and

type I diabetes Type 1 diabetes (T1D), formerly known as juvenile diabetes, is an autoimmune disease that originates when cells that make insulin (beta cells) are destroyed by the immune system. Insulin is a hormone required for the cells to use blood sugar for ...

. Research has shown that the season a baby is born in can have a major effect on whether or not they will become a heavy smoker. This even varies between men to women.

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. In addition, they uncovered an association between cardiovascular diseases and birth month. This was subsequently confirmed in a separate study, also using data from NYC. 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. 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. The relationship between birth month/season and increased risk of cardiovascular disease was also confirmed in a study of close to 130,000 canines. The birth season association was found among dogs not genetically predisposed to cardiovascular disease.

As a factor in infant growth

The season during which a birth takes place has been linked to the weight development of the infant as well as initial weight.

As a factor in academic development

There is evidence that suggests that children who are born earlier while they attend the same academic year with others, gain an advantage: :"''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).''"

As a suicide risk factor

Birth rates of people who later complete a 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%). Research works in Sweden show that those who preferred 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.

References

{{reflist Seasonality Child development Human reproduction