A woman takes asthma medication with an inhaler in Helsinki. The picture shows GSK's Ventoline discus. LEHTIKUVA


A recent study suggests that children with older siblings are less likely to need allergy and asthma medication, highlighting the potential protective effect of sibling exposure during the early years of life. This finding supports the microbiome hypothesis as a significant factor in preventing asthma and allergic conditions.

Conducted by the University of Helsinki and the Social Insurance Institution of Finland (Kela), the research analyzed data from over half a million Finnish children born between 1995 and 2004.

It examined the likelihood of purchasing medications for allergic rhinitis, atopic dermatitis, asthma, and severe allergic reactions among Finnish children aged 0–15, considering the number of siblings, birth order, and age differences between siblings.

The study acknowledges the long-standing observation that firstborn and only children have a higher incidence of allergic diseases compared to those growing up with siblings. "Previous studies couldn't eliminate other explanatory factors such as cesarean sections, living environment, and genetic differences," says Juha Luukkonen, co-lead researcher from the University of Helsinki.

The analysis took into account various potential confounders, including the method of birth, urban versus rural living environments, socioeconomic status of the family, and, through sibling comparison, shared genetic and environmental factors among siblings.

Heta Moustgaard from Kela, another lead researcher in the project, emphasized the strong support the results provide for the microbiome hypothesis as an explanation for asthma and allergy symptoms. This hypothesis suggests that microbial exposure caused by siblings can protect against the development of asthma and allergies.

The research, published in the European Journal of Epidemiology, also considered factors such as birth method and residential environment, further reinforcing the potential benefits of sibling exposure in protecting against allergic diseases. This study adds to the growing body of evidence on the importance of early-life environmental factors in the development of immune-related conditions.