Do babies born in winter tend to be more irritable? (No.) Are summer babies more likely to be thrill-seekers? (Yes.) While there’s no best or worst month for a child to be born, each season does seem to have its own quirks. Babies born in spring, for instance, tend to have a lower risk of ADHD and asthma than children born at other times of the year, says Mary Regina Boland, a predoctoral fellow in the department of biomedical informatics at Columbia University in New York City and lead author of a 2015 study on birth month and disease risk in the Journal of the American Medical Informatics Association.
Many studies on birth season have their own biases (for instance, Boland’s only looked at New York City babies). But a relatively robust science of birth seasons does seem to be emerging. Here’s what research says about spring babies.
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They may be more optimistic
Spring babies may be more likely to grow into optimistic children and adults. In a small study published in the Journal of Affective Disorders, researchers found that a hyperthymic temperament (meaning extremely positive) was more common in participants who were born in the spring and autumn. Those born in summer and winter, on the other hand, were more likely to have a depressive temperament. Other studies have linked higher levels of dopamine and serotonin (neurotransmitters thought to ward off depression) in people born in the spring. This is good news for those with a spring birthday, since a slew of research suggests positive thinking is good for your overall health (it may benefit your heart, blood pressure, and recovery from surgery, for example).
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They may have a lower risk of asthma
The highest rates of asthma in Boland’s 2015 study occurred in people born in July, August, September, and October, with lower levels among babies born at other times of the year, including the spring. “We believe that the high heat and high humidity [in September] increased dust-mite breeding,” says Boland. Dust mites are a major asthma trigger, especially in urban areas (the study looked at medical records from New York-Presbyterian/Columbia University Medical Center over a 100-year period). If the critters are in abundance during the first two months of life, she explains, it’s possible that they could affect how well the immune system develops.
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They could also be less likely to be diagnosed with ADHD
ADHD tends to peak among babies born late in the year, with lower rates among spring births. But this may be less a result of biology than of cut-off times for the school year. In the U.S. school system, the youngest children in any class are usually those born in November and December. “The hypothesis is that they’re younger and simply not as calm as their older peers,” explains Nicholas Tatonetti, PhD, co-author on Boland’s study and assistant professor of biomedical informatics at Columbia. This may lead to more ADHD diagnoses. “It’s not really an environmental finding. It’s more of a cultural phenomenon,” he adds.
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They could have higher risk for heart disease
Boland’s study also saw an increased risk of heart disease in spring babies, specifically those born in March. And not just one type of heart disease, but several—including atrial fibrillation (a type of irregular heart rhythm) and congestive heart failure.
“There was a cluster of several different cardiovascular diseases, which may mean exposure to some environmental factors for those born in the spring causing some slight defect in the heart leading to longer-term consequences,” says Tatonetti. However, more research on this is needed.
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March and April may be good months for breeding future leaders, according to a study from the University of British Columbia of 375 CEOs from major corporations. Researchers found that 12.53% of S&P 500 CEOs were born in March and 10.67% in April, compared to only 6.3% in June and 5.87% in July. As with the lower rate of ADHD among spring babies, this could have more to do with your place in the classroom than your birth season. People born in the spring are among the older members of their class and are naturally groomed to lead.
“They’re usually the oldest in their year, so they develop the longest, the strongest, and the largest,” says Tatonetti. “They get the most attention and this propagates through life.”
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They may be night owls
People born in the sun-drenched seasons of spring and summer may be more likely to go to bed later at night than folks born at other times of the year. The authors of a 2009 study in the journal Sleep found that participants who were born in spring and summer preferred to go to bed earlier than those born in the fall and winter. Birth season, however, didn’t affect what time people woke up. The researchers noted that wakeup time could have more to do with culture and work schedules, which, in turn, were strongly linked to nationality.
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Several studies have found that people born in spring tend to have a higher rate of developing multiple sclerosis (MS) later in life. The association tended to be even stronger in areas where MS is widespread, namely locations far from the equator. Researchers have noticed that May babies tend to have higher levels of a type of potentially harmful immune cell which may be involved with MS, as well as lower levels of vitamin D in their blood—another factor that could possibly influence who develops the disease.
However, birth season is just one of myriad factors playing into how babies develop. “Probably there is some real mechanism here, but the risk contributed by the seasonality of birth is very small relative to other factors such as diet and exercise,” says Tatonetti.