“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.
For the study, Kusunoki and colleagues looked at the significance of the birth order effect on the prevalence of asthma, atopic dermatitis, allergic rhinitis, allergic conjunctivitis and food allergy. A survey was administered to parents of more than 13,000 children between the ages of 7 and 15. The data was then examined and the incidence of each allergic disease was compared with birth order.
According to the results, there was no significant difference in the prevalence of asthma or atopic dermatitis according to birth order. However, the prevalence of rhinitis, conjunctivitis and food allergy decreased significantly as birth order increased. For example, the prevalence of food allergy was 4% in first born children, 3.5% in second born children and 2.6% for children born later.
When looking specifically at the presence of food allergy in the children during infancy, the same effect was also observed. The incidence of food allergy decreased significantly as birth order increased, leading the researchers to suggest that this birth order effect may have a prenatal origin.
“Further evaluation should shed light on the role of pre-, peri- and post-natal circumstances on the development of childhood allergy,” said Kusunoki.
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- This study was presented during the 2011 Annual Meeting of the American Academy of Allergy, Asthma & Immunology (AAAAI) on March 18-22 in San Francisco. However, it does not necessarily reflect the policies or the opinions of the AAAAI.
- A link to all abstracts presented at the Annual Meeting is available at www.annualmeeting.aaaai.org
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Note to media: See abstract 525