By Sandy Hemphill, Contributing Writer, BabyMed
Conversations about siblings and birth order often center around personality characteristics but birth order seems to affect health, too. The most recent health-related finding is that the first child seems somehow to protect younger siblings from allergies and asthma. How this works isn’t clearly understood at this point but some interesting theories are spurring further research.
Medical studies from as far back as 1989 indicate the first child is the most likely child in a family to suffer hay fever, asthma, and other allergic reactions to airborne dust and pollen particles. Some researchers believe this persistent outcome isn’t because the first child is the most immunologically delicate; they suspect the first child triggers some sort of immunological protection for siblings that follow.
A recent study from the Technical University of Denmark indicates this older-sibling protection comes early for younger siblings. Susanne Brix Pedersen, a systems biologist at the Danish university and co-author of the study, conducted immunological studies on 571 infants only 1 month old. Some were firstborn children for their families but others had at least one older sibling.
Natalie Jacewicz, writing for NPR, described the study in a way parents of young kids will understand: “Like many things concerning small children, the study involved snot — the researchers collected samples from each infant's nose.” The samples were tested for proteins that trigger a response from the immune system when an allergen is present.
The noses of firstborn children had fewer of these proteins that protect against allergic reactions than the noses of children with at least one older sibling. This finding indicates the firstborn children were more sensitive to allergens than children with an older sib.
Brix Pedersen’s study does not indicate when or how this immunological protection comes about but some theories from the research team include:
- The first pregnancy may allow the mother’s immune system to recognize and tolerate other fetuses fathered later by the same man.
- Babies with an older sibling may benefit from the germs the older sibling collects during its daily routine.
The Danish study found the immunologically protective effect of an older sibling diminished when there were long periods of time between pregnancies. Speculation as to why this occurs includes:
- Whatever biochemical protections that might occur in the womb during the first pregnancy may diminish as time elapses between pregnancies.
- The older the first child becomes, the cleaner his/her personal hygienic practices become.
Brix Pedersen and her research team plan to keep up with the 571 babies in their study to document any changes in immunological health and development of asthma and allergies occur as they grow up.
Source:
Brix Pedersen, S, et al. "Siblings Promote a Type 1/Type 17-oriented immune response in the airways of asymptomatic neonates."PubMed. Allergy / European Academy of Allergy and Clinical Immunology (John Wiley & Sons Ltd), 7 June 2016. US National Library of Medicine / National Institutes of Health. Web. 29 June 2016.
Jacewicz, Natalie. "Asthma-Free With No Hay Fever? Thank Your Older Sibling."NPR / Shots. NPR, 22 June 2016. Web. 29 June 2016.
"Asthma: Kids."CDC / Centers for Disease Control and Prevention. US Department of Health and Human Services, 30 Apr. 2013. Web. 29 June 2016.