150 Medical Conditions Tied to Birth Order, Researchers Report

How a Child's Position in the Family Relates to Health Risks

According to НВ — Техно: Researchers from the University of Chicago and Columbia University have published findings connecting sibling birth order to health outcomes. The study, released on August 7 in the journal Nature Health, drew on medical records from more than 10.3 million children who each had exactly one sibling. After reviewing 569 clinical conditions, the team identified 150 that clearly varied according to whether a child was born first or second.

Distinct Health Profiles for Firstborns and Second-Born Children

Firstborn children were more likely to receive diagnoses involving allergic reactions, along with neuropsychiatric and neurodevelopmental conditions, including:

• attention-deficit/hyperactivity disorder (ADHD),
• autism spectrum disorders,
• Tourette syndrome,
• obsessive-compulsive disorder (OCD).

Second-born children, by contrast, showed higher rates of:

• digestive system disorders,
• gastrointestinal issues,
• migraines,
• shingles,
• a tendency toward psychoactive substance use.

The analysis compared outcomes both within individual families and across different households. A notable finding: when a larger age gap separated siblings, the older child's allergy risk was reduced, and the younger sibling might not develop those allergies.

The scientific community plans to continue investigating this phenomenon to uncover the biological and environmental mechanisms behind these health differences related to birth order.

Birth order has long been a topic of curiosity for parents and researchers, yet large-scale medical evidence has remained scarce. These findings underscore how family environment and biological factors may interact to shape childhood health. Because the results point to distinct risks for different birth positions in a family, they could inform family planning and pediatric guidance. Future research may expand this understanding and lead to prevention strategies tailored to a child's place in the sibling order.