Firstborns more prone to ADHD and autism, study finds

A large-scale study analyzing medical data from 10 million sibling pairs in the United States has revealed notable differences in health conditions between firstborn and second-born children.

The research, spanning two decades and examining 569 categories of ailments, identified significant disparities in 150 of them, directly linked to birth order. Firstborn children exhibited a higher probability of diagnoses including autism, ADHD, Tourette syndrome, and obsessive-compulsive disorder. Allergic conditions, such as food allergies, were also more frequently observed in the eldest siblings.

While the study highlights these correlations, the exact causes remain unclear. Dr. Marc Siegel, speaking to Fox News, suggested potential factors such as differing parental attention levels, with firstborns possibly receiving more stimuli due to greater parental focus. He also hypothesized that the immune system's initial interactions with the environment might play a role in the observed allergy rates in firstborns.

Conversely, second-born children in the study were more prone to migraines, shingles, gastritis, and issues related to substance abuse. The researchers noted that factors like changes in the mother's body after the first pregnancy, the children's environment, and shifts in parental behavior between the first and second child could contribute to these differences. However, the study emphasizes that birth order itself is not a definitive cause of these conditions, and other variables like parental age, age gaps between siblings, and family dynamics may also be influential.

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The study raises many questions, and the causes of the observed differences between siblings are not yet clear.