Study Ties Birth Order to 150 Diseases in 10 Million People
Updated
Updated · Newsweek · Aug 4
Study Ties Birth Order to 150 Diseases in 10 Million People
3 articles · Updated · Newsweek · Aug 4
Summary
More than 10 million people across 5.1 million U.S. families were analyzed in a Nature Health study that found statistically significant birth-order links across 150 diseases.
First-born children showed higher diagnosis rates for autism, ADHD, Tourette syndrome, OCD, food allergies, allergic rhinitis, asthma and acne; second-borns had 43% lower odds of one pervasive developmental disorder.
Younger siblings were more likely to be diagnosed with substance abuse, migraines, gastritis, biliary tract disease, kidney infections and herpes zoster, extending the pattern beyond mental health and allergies.
Researchers said the associations likely reflect a mix of biology, environment and family dynamics—including microbial exposure, parental age, healthcare use and sibling influence—rather than birth order itself causing disease.
The authors cautioned that most effects were modest and based on insurance claims from two-child, employer-insured families, limiting how broadly the findings can be applied.