A new Cambridge University study found that the season in which you were born can influence how healthy you end up becoming as an adult.
The “healthiest” birth months, per the study, were June, July, and August.
Researchers analyzed growth and development data of about 450,000 men and women from the U.K.’s Biobank study, a national resource databank that is commonly used to study disease development. The results were published in the journal Heliyon.
Scientists determined that a person’s birth month affects birth weight, and for girls, it also impacts when they start puberty. Combined, those two factors have an impact on a woman’s overall health as an adult. (Scientists also found it affected the overall health of men but saw a stronger correlation in women.)
Birth weight, the age at which a woman started her period, and her height were “highly significantly associated” with when she was born, researchers said in the study.
More specifically, children who were born in the summer were slightly heavier at birth, ended up being taller as adults, and went through puberty slightly later than their winter-born counterparts.
Scientists also noticed an “abrupt difference” between children born in August and those born in September.
What’s going on here?
Researchers speculate that it may be due to in utero vitamin D exposure. Pregnant women are likelier to be in the sun more during the summer months and, as a result, are exposed to more vitamin D. Also, school usually starts in September, leading more people to be indoors, which could explain the significant change between August and September babies.
Something about that vitamin D may help babies become heavier and experience puberty earlier, researchers say.
But while researchers think there’s a link, they’re not exactly sure why it exists. “We think that vitamin D exposure is important, and our findings will hopefully encourage other research on the long-term effects of early-life vitamin D on puberty timing and health,” lead study author John Perry, a senior investigator scientist at the University of Cambridge, said in a press release.
This isn’t the first time a person’s birth month has been linked to adult health. A study published earlier this year in the Journal of the American Medical Informatics Associationfound that people born in May have the lowest risk of developing disease, while those born in October had the highest. Babies born in the late winter or early spring were also more likely to have heart disease.
Of course, this isn’t the be all and end all for health. It’s possible to have been born in January and be incredibly healthy, just as it’s possible to be a June baby and not be the picture of health.
But consider yourself lucky if you were a summer baby: You might have a leg up on everyone else.