Not a pro athlete? Blame your birthday

A Post by: Ellaheh Gohari

June 29, 2023

Although zodiac signs have no scientific basis, there does seem to be a correlation between birth month and athletic success. Known as the “birthday effect,” it’s a phenomenon that appears across several sports, where the percentage of athletes born in certain months is much higher or lower than the general population. But why?

The main explanation for professional athletes’ skewed birthday prevalence compared to the general population lies as far back as elementary school. In elementary school, an age difference of mere months can make a huge difference in terms of biological development, with kids born in the earlier months of the school generally larger and more developed than those born later. This makes them ideal players for sports like ice hockey and baseball.

After being identified early, these players begin to develop their skills. Although the playing field evens out with each coming year and birth month stops playing much of a role in size, players who were born earlier and thus were larger initially may have had more time to hone their skills, potentially making them better in their sport. And indeed, both ice hockey and baseball’s professional leagues see a much greater prevalence of players born in the beginning of the school selection year. The birthday effect isn’t just an American phenomenon either; a higher prevalence of European and South American soccer players are born in the first quarter of the grade school year than the general population.

Several studies have shown the birthday effect in action. One such study determined that, when testing children and adolescents in the same grade in lower body power, handgrip strength, and cardiovascular health, November-born children were the most fit, whereas those born in April, May, and June were the least. This supports the theory behind the birthday effect, since those born in April, May, and June are generally some of the youngest students in school as the cutoff is sometime in the summer, meaning they likely will be the smallest and thus weakest at this early age.

Furthermore, the study posits that another reason why fall babies/children tend to be stronger is because during pregnancy, their mothers had greater exposure to Vitamin D due to being pregnant throughout spring and summer. Vitamin D has a positive correlation with muscle growth.

Whatever the reason, birth month isn’t everything. Being born in November won’t make you an elite athlete, just as being a June-baby or an April one, like me, won’t doom you to forever watching sports from the sidelines. A combination of genetics, training, dedication, and even luck determines who will shine in the stadium and who is best fit in the stands.