A massive study examining medical records of about 10 million American siblings over two decades found that birth order may be associated with certain health conditions. Researchers from the University of Chicago and Columbia University analyzed 569 disease categories across families and between siblings, identifying 150 conditions that showed statistically significant associations with birth order.

Findings

The findings suggest first-born and second-born children can show different patterns of health risks, although researchers emphasize that the study does not establish that birth order directly causes any particular disease. First-born children in the study were more likely to have several neurodevelopmental and psychiatric diagnoses, including autism, ADHD, Tourette’s syndrome and obsessive-compulsive disorder. They also showed higher rates of some immune-related and allergic conditions, including food allergies.

Second-born children, meanwhile, showed higher statistical rates of migraines, shingles, substance use disorders and gastrointestinal conditions such as gastritis. The research was published in the journal Nature Health.

Expert Insights

Fox News senior medical analyst Dr. Marc Siegel said the findings raise important questions about why health patterns might differ between children in the same family. “I love this study because it opens a lot of questions more than it gives answers,” Siegel said. He offered several possible explanations, while making clear that those explanations are theories rather than conclusions established by the research.

For the higher rate of ADHD among first-born children, Siegel suggested that differences in parental behavior could play a role. “My theory, they get more stimuli,” he said, describing parents as potentially being more closely focused on their first child. He also suggested that differences in early environmental exposure could potentially influence the development of allergies. “I think it’s because the firstborn’s immune system hasn’t seen the environment before,” Siegel said.

Original reporting: WOWO News/Talk (Fort Wayne) — read the source article.