I found this article compelling, particularly the part about cow's milk intolerance. Both of my ADHD children had severe milk protein allergies as infants. One has asthma, and the other has a nut allergy.
http://www.medicalnewstoday.com/articles/264854.php
"Children with a history of asthma and various allergies may be at higher risk of developing ADHD (attention deficit hyperactivity disorder), according to a study published in the journal Annals of Allergy, Asthma and Immunology."
Do any of you have asthma or allergies?