Borns More Likely to Develop These 4 Diseases, Scientists Say

Key Points:

• A study published in Nature Health analyzed data from over five million two-child families and found that birth order influences the risk of developing certain diseases, with first-borns more prone to neurodevelopmental and immune-allergic conditions, and second-borns more likely to develop gastrointestinal and substance abuse disorders.
• First-born children showed a 26% higher risk of autism, 7% higher risk of ADHD, 20% higher risk of food allergies, and 9% higher risk of hay fever, while second-borns had a 19% higher risk of substance abuse and 14% higher risk of gastrointestinal conditions.
• Researchers suggest potential explanations include biological differences between pregnancies, immune system adaptations, shared microbiomes among siblings, and variations in parental behavior and healthcare-seeking patterns.
• Experts caution that the study shows correlation rather than causation, and that birth order is a relatively weak and non-modifiable risk factor compared to others like sex or family medical history, meaning individual disease risk remains influenced by many factors.
• The findings highlight population-level trends rather than individual predictions, and further research is needed to understand the mechanisms behind birth order-related health differences.