Health A study of more than 10 million siblings suggests that firstborns are more likely to be autistic and have allergies, while conditions like migraine and shingles tend to affect their younger sibling Facebook / Meta Twitter / X icon Linkedin Reddit Email A lot of stereotypes around sibling structures don’t stack up, but being the first or second child in a family may actually affect your health iStockphoto In a family of two children, whether you were born first or second may shape your likelihood of developing more than 150 conditions, according to the largest study of its kind. Researchers analysed data from more than 10 million siblings and found associations between birth order and everything from autism and anxiety to hay fever. Birth order has fascinated scientists for more than a century, with attempts being made to identify links with personality traits and IQ. However, many older studies have been criticised for cherry-picking data or failing to control for confounding factors.…