After all, eating Big Brother's snot might not be a bad idea

From the moment we are born, the small world around us contributes to the unique composition of our microbiota. The microbes we are exposed to differ depending on whether we are born via c-section, are breastfed, grow up on a farm, have a dog... or have brothers and sisters! To assess the impact of siblings on the development of the microbiota, the researchers analyzed the composition of the gut flora (from 1 week to 6 years of age) and pharyngeal microbiota (from 1 week to 3 months of age) of nearly 700 children. The samples were regularly renewed, with nearly 4,500 samples sequenced in all. At each stage, the researchers took into account the child’s family situation, i.e. only child or presence of older/younger sibling(s). They also noted about 15 additional factors that may influence a child’s microbiota, from birth weight to household income. Lastly, they compared the data collected from the children with the presence of asthma, allergic rhinitis, and sensitization to various allergens at age six.

Microorganisms in microbiota have family spirit 

The researchers found that having siblings during early childhood was one of the most important determinants of the composition of the gut microbiota and airway microbiota. This effect was most pronounced in children in their first year of life with older siblings. Their gut microbiota was richer, more diverse, and more mature than that of only children. Furthermore, a large family is not necessary, since having one older sibling close in age mattered more than having a number of siblings. The consolation for only children: the difference between their microbiota and that of children with siblings subsides by age four.

Influence of siblings on infants’ respiratory microbiota greater than that of breastfeeding

What about the airway microbiota? During the first three months of life, it too was modified to a greater extent by the presence of a sibling than by other major factors, such as breastfeeding or antibiotic use. The microbiota of babies with siblings was less diversified than that of babies with no siblings. However, unlike the gut microbiota, lower bacterial diversity in the airways appears to be favorable to respiratory health.² 

What does the study tell us? Having siblings in early childhood impacts microbiota development and health. On the other hand, siblings make it easier for children to be contaminated by microbes that cause colds and other illnesses. However, the researchers believe that early exposure to relatively harmless microbes can reduce the risk of allergic diseases.³