A study analyzing medical data from 10 million U.S. siblings over two decades suggests that birth order may be associated with specific long-term health risks. Researchers from the University of Chicago and Columbia University examined 569 disease categories and identified 150 conditions significantly linked to whether a sibling is older or younger.
First-born children showed a higher likelihood of neurodevelopmental and psychiatric diagnoses, including autism, ADHD, Tourette's syndrome, and OCD, along with immune-allergic conditions such as food allergies. In contrast, second-born children were more prone to migraines, shingles, substance use disorders, and gastrointestinal issues like gastritis.
Dr. Marc Siegel, senior medical analyst for Fox News, discussed the study's implications, noting that it raises more questions than it answers. He proposed that first-born children may receive more parental attention, which could influence their health outcomes. Siegel also suggested that environmental exposure plays a role in the prevalence of allergic conditions among first-borns.
The study highlights correlations rather than direct causation, indicating that the observed trends may not be solely due to biological factors but could also involve social dynamics and healthcare-seeking behaviors. Researchers pointed out that factors such as parental age and sibling age gaps complicate these associations. The findings suggest that birth order may serve as a modest risk marker rather than a definitive health predictor. The research was published in the journal Nature Health.