US study links birth order to different health risks

A study conducted by researchers at the University of Chicago and Columbia University has identified significant differences in health conditions based on birth order. Analyzing two decades of medical data from 10 million siblings in the United States, researchers examined 569 categories of conditions and found meaningful variations in 150 of them.

First-born children showed a higher probability of being diagnosed with autism, ADHD, Tourette syndrome, and obsessive-compulsive disorder, as well as various allergic conditions, including food allergies. In contrast, second-born children were more frequently diagnosed with migraines, shingles, gastritis, and substance use disorders.

Dr. Marc Siegel noted that while the causes of these differences are not yet clear, hypotheses include varying levels of parental attention or how a child's immune system reacts to environmental stimuli during their first contacts.