Birth Order Linked to Broad Disease Risk in Millions of Kids
A large US study of over 10 million children with at least one sibling analyzed 569 diseases and found birth order is linked to widespread health differences: first-borns have higher risk for neuropsychiatric conditions such as ADHD and autism, while second-borns show higher risk for stomach problems and other digestive issues. About 150 diseases showed birth-order differences, with results consistent across within-family and between-family comparisons; some risks vary with age gaps between siblings, and researchers say mechanisms remain to be clarified.
