"ADHD, a chronic mental health disorder, is most commonly found in males, while asthma is also more common in young boys than girls," said Eelko Hak, lead author of the study published in journal Annals of Allergy, Asthma & Immunology.
"We found there is an increased risk of ADHD in boys with a history of asthma and an even stronger risk associated with milk intolerance," Hak said.
Researchers in the Netherlands and Boston studied 884 boys with ADHD and 3,536 boys without the disorder. Of the children with ADHD, 34 per cent had asthma and 35 per cent had an allergic disorder.
"Further research is needed to understand why there appears to be an increased risk of developing ADHD in children with allergy and asthma," said Gailen Marshall, editor-in-chief of Annals of Allergy, Asthma & Immunology.
"Medications for these conditions far outweigh the risks, and can be life-saving in some conditions. Treatment should not be stopped, unless advised by a board-certified allergist," Marshall said.