First-born children may be more likely to suffer from certain allergic conditions, according to new research presented at the Annual Meeting of the American Academy of Allergy, Asthma & Immunology.
“It has been established that individuals with increased birth order have a smaller risk of allergy. However, the significance of the effect may differ by allergic diseases,” explained Takashi Kusunoki, MD, PhD, first author of the study.
A survey was administered to parents of more than 13,000 children between the ages of 7 and 15. According to the results, there was no significant difference in the prevalence of asthma or atopic dermatitis according to birth order.
However, as birth order increased, the prevalence of rhinitis, conjunctivitis and food allergy decreased significantly. For example, the prevalence of food allergy was 4 percent in first-born children, 3.5 percent in second-born children and 2.6 percent for children born later.
“Further evaluation should shed light on the role of pre-, peri- and post-natal circumstances on the development of childhood allergy,” said Kusunoki.
Researchers hypothesize the results may have something to do with changes in the womb or prenatal environment, or it could be related to the home environment – more children in the house means more germs – exposing younger siblings to more at an earlier age than their elder siblings.