Scientists have long debated whether birth order shapes personality.Now, a study of more than 10 million Americans suggests your place in the family could also influence your lifelong health.Researchers found links between family position and the risk of 150 health conditions, including autism, ADHD, allergies and digestive disorders.Firstborn children were more likely to develop a range of neurodevelopmental conditions, including autism, ADHD, Tourette's syndrome and obsessive-compulsive disorder (OCD). They also had higher rates of food allergies, hay fever, asthma and acne than their younger siblings.Second-born children, meanwhile, were less likely to be diagnosed with many neurodevelopmental conditions. The researchers found they were 43 percent less likely than firstborns to develop certain autism-related disorders.However, they had higher rates of digestive, musculoskeletal and infectious diseases, as well as substance abuse disorders, migraines, stomach problems, kidney infections and herpes zoster – the virus that causes shingles. Firstborn children showed the strongest links to brain development and allergy–related conditions, while second–born children had higher rates of digestive, musculoskeletal, and infectious diseases, according to the study's chart