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US study on birth order and health correlations

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2026-08-16 22:12 UTC → 2026-08-19 16:42 UTC · added ~~removed~~

Researchers from the University of Chicago and Columbia University conducted a large-scale epidemiological study analyzing two decades of medical data from approximately 10 million siblings in the United States. The study, published in the journal Nature Health, examined 569 disease categories and identified significant correlations between birth order and 150 different health conditions. Findings indicate that first-born children have a higher prevalence of neurodevelopmental and psychiatric diagnoses, such as autism, ADHD, Tourette syndrome, and obsessive-compulsive disorder, as well as immune-mediated allergic reactions like food allergies. Conversely, second-born children showed a higher statistical likelihood of experiencing migraines, shingles, substance use disorders, and gastrointestinal issues like gastritis. Subsequent analysis of data from 5 million American families suggests that birth order may also influence life expectancy. Findings indicate that second-born children may face higher mortality rates, potentially linked to lifestyle factors and substance abuse, alongside gastrointestinal problems and infections such as herpes zoster. While the study establishes these correlations, researchers noted that direct causation has not been proven. Dr. Marc Siegel suggested that potential hypotheses for these variations include differences in parental attention or how a child’s immune system responds to environmental stimuli. Scientists emphasized that the study is limited to families within the United States and noted that healthy lifestyle choices can mitigate many of these statistical risks.

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