“To every thing there is a season, and a time to every purpose under the heaven.”
The month of birth is not just relevant to one’s astrological sign. It may have medical consequences. An impressive number of published studies have found that the month and season of birth may be related to a higher risk of various medical and psychiatric disorders.
For decades, it has been reported in more than 250 studies1 that a disproportionate number of individuals with schizophrenia are born during the winter months (January/February/March in the Northern Hemisphere and July/August/September in the Southern Hemisphere). This seasonal pattern was eventually linked to the lack of sunlight during winter months and a deficiency of vitamin D, a hormone that is critical for normal brain development. Recent studies have reported that very low serum levels of vitamin D during pregnancy significantly increase the risk of schizophrenia in offspring.2
But the plot thickens. Numerous studies over the past 20 to 30 years have reported an association between month or season of birth with sundry general medical and psychiatric conditions. Even longevity has been reported to vary with season of birth, with a longer life span for people born in autumn (October to December), compared with those born in spring (April to June).3 Of note, a longer life span for an individual born in autumn has been attributed to a higher birth weight during that season compared with those born in other seasons. In addition, the shorter life span of those with spring births has been attributed to factors during fetal life that increase the susceptibility to disease later in life (after age 50).
The following studies have reported an association between month/season of birth and general medical disorders:
- Higher rate of myopia for summer births4
- Tenfold higher risk of respiratory syntactical virus in babies born in January compared with October, and a 2 to 3 times higher risk of hospitalization5
- Higher rates of asthma during childhood for March and April births6
- Lower rate of lung cancer for winter births compared with all other seasons7
- An excess of colon and rectal cancer for people born in September, and the lowest rate for spring births8
- Lowest diabetes risk for summer births9
- For males: Cardiac mortality is 11% less likely for 4th-quarter births compared with 1st-quarter births. For females: Cancer mortality is lowest in 3rd-quarter vs 1st-quarter births10
- The peak risk for both Hodgkin and non-Hodgkin lymphoma is for April births compared with other months11
- A strong trend for malignant neoplasm in males was reported for births during the 1st trimester of the year (January through April) compared with the rest of the year12
- Higher rate of spring births among patients who have insulin-dependent diabetes13
- Breast cancer is 5% higher for June births compared with December births14
- Higher risk of developing an allergy later in life for those born approximately 3 months before the main allergy season.15
The above studies may imply that birth seasonality is medical destiny. However, most such reports need further replication, or may be due to chance findings in various databases. However, they are worth considering as hypothesis-generating signals.
Continue to: And now for the risk of psychiatric disorders...