Being the oldest or youngest sibling may change your risk of diseases

Embargoed until: Publicly released: 2026-08-03 19:00

International

What does this mean?

Jump to: MultimediaAttachmentsExpert Reaction

Whether you are the oldest or youngest sibling could affect what diseases and conditions you get, a new study shows. Researchers compared siblings in over 5 million US families with 2 children. First-borns were more likely to have allergies and conditions like autism, ADHD, Tourette’s and OCD. Second-borns were more likely to have stomach problems, migraines, shingles and substance abuse issues. Age gaps impacted some of these differences, with a 4-6 year gap increasing the likelihood that a first-born child would have autism. The researchers said that these differences are likely due to a combination of biological and social factors influencing children’s lives.