Birth Order Linked to Distinct Disease Risks in 10‑Million‑Person US Study

birth order disease risk neurodevelopmental disorders substance abuse phenome study

Researchers analyzed more than 10 million individuals from about five million two‑child families in the United States using the Merative MarketScan commercial claims database (2003‑2024). The phenome‑wide assessment mapped 569 diagnoses and compared disease odds between first‑born and second‑born siblings.

First‑born children showed higher odds of neurodevelopmental and immune‑allergic conditions, including autism, attention‑deficit/hyperactivity disorder, Tourette syndrome, obsessive‑compulsive disorder, food allergies, allergic rhinitis, asthma, hay fever and eczema. In contrast, second‑born siblings had higher odds of substance‑abuse diagnoses and gastrointestinal disorders such as gastritis and duodenitis, as well as increased risk for infections like herpes zoster.

The authors suggest that early microbial exposure from older siblings may protect younger children from allergic diseases, while social and behavioral factors could explain the greater substance‑use risk among later‑born children. The study, published in Nature Health, provides the first large‑scale disease atlas linking birth order to health outcomes across the human phenome.

Entities

Columbia University · Merative MarketScan database · Nature Health · Nature Health (journal) · United States · University of Chicago · first‑born children · second‑born children

Claims

What the coverage asserts, and how many sources carry each claim.

[● 3 SOURCES] Later-born children have higher risk of substance abuse. www.elperiodico.digital · arabic.euronews.com · es.euronews.com
[● 3 SOURCES] The authors suggest the differences are due to early microbial exposure, parental attention, and social modeling. www.elperiodico.digital · arabic.euronews.com · es.euronews.com
[● 3 SOURCES] Researchers from the University of Chicago and Columbia University analyzed data from more than ten million Americans in families with two children. www.elperiodico.digital · arabic.euronews.com · es.euronews.com
[● 3 SOURCES] The study identified associations between birth order and risk for about 150 diseases. www.elperiodico.digital · arabic.euronews.com · es.euronews.com
[● 3 SOURCES] Firstborns have higher risk of neurodevelopmental disorders such as autism, ADHD, Tourette syndrome, and OCD. www.elperiodico.digital · arabic.euronews.com · es.euronews.com
[● 3 SOURCES] Later-born children have higher risk of gastrointestinal problems and infections such as herpes zoster. www.elperiodico.digital · arabic.euronews.com · es.euronews.com
[● 3 SOURCES] Firstborns have higher risk of allergies, asthma, and acne. www.elperiodico.digital · arabic.euronews.com · es.euronews.com
[● 3 SOURCES] Firstborn children have higher risk of hypertension and heart disease compared to later-born siblings. www.elperiodico.digital · arabic.euronews.com · es.euronews.com