In Japan, researchers recently surveyed the parents of more than 13,000 children between the ages of 7 and 15 to find out whether birth order seemed to influence whether the child suffered from allergies. While they found that children's birth order did not seem to impact the prevalence of asthma or exzema, they did find that firstborn children were more likely to have hay fever and food allergies.
According to US News, the research team found that 4 percent of firsborn children had food allergies (http://health.usnews.com/health-news/family-health/allergy-and-asthma/articles/2011/03/20/firstborn-kids-seem-to-have-more-food-allergies-hay-fever). This is compared to a food allergy rate of 3.5 percent in those who were the second child in their family, and a rate of just 2.6 percent for subsequent children.
"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," said Dr. Takashi Kusunoki, first author of the study. Kusunoki and his colleagues concluded that more research is needed to find out how birth order affects the risk of food allergies in children.
The researchers presented their findings last week at the annual meeting of the American Academy of Allergy, Asthma & Immunology in San Francisco.