Birth order may influence long-term disease risk

A study published in Nature Health involving over 10 million siblings suggests that birth order may influence long-term health risks. Analyzing medical records from more than five million American families with two children, researchers identified statistically significant differences in 150 out of 418 analyzed diseases.

First-born children showed a higher probability of being diagnosed with autism, ADHD, tics, food allergies, and allergic rhinitis. In contrast, second-born children demonstrated higher likelihoods of gastritis, herpes zoster, and issues related to substance abuse.

Researchers suggest biological and environmental factors may play a role. For instance, the lack of exposure to microbes from older siblings in the home might contribute to higher allergy rates in first-borns. The study notes that while these associations exist, they do not prove causality, and results may be influenced by parental attention levels and socioeconomic factors.