What is already known
Growing up with siblings has been linked to various health outcomes, including a reduced risk of inflammatory bowel diseases and allergies. Some studies have reported that having siblings may also influence the gut microbiota composition, but evidence remains scarce.
What this research adds
Researchers assessed the airway and gut microbes of nearly 650 children from one week of age until six years. They found that, especially in the first year of age, the presence of older siblings was among the most important factors to influence the composition of the airway and gut microbiota. The age gap to the closest older sibling had the strongest influence, with smaller age gaps being associated with a more diverse gut microbiota and a less diverse airway microbiota. The sibling signature in the gut microbiota at one year of age was linked to a decreased risk of asthma at six years.
Conclusions
The findings suggest that older siblings can influence the development of the gut and airway microbiota in children.
Growing up with siblings has been linked to a reduced risk of inflammatory bowel diseases and allergies. Now, researchers have found that older siblings may also influence the development of the gut and airway microbiota in children.
The findings, published in the journal Microbiome, highlight the need to consider siblings in all studies involving the developing microbiota.
Having siblings, the researchers say, “has been linked to numerous health outcomes and is also an important determinant for the developing microbiota. Nonetheless, research into the role of having siblings on the developing microbiota has mainly been incidental.”
To fill this gap in knowledge, researchers led by Søren Johannes Sørensen, Morten Arendt Rasmussen, Hans Bisgaard and Jakob Stokholm at the University of Copenhagen assessed the airway and gut microbes of nearly 650 children from one week of age until six years.
Sibling influence
At one week, nearly 60% of the participating children had one or more older siblings. At six years, only 11% had no siblings, whereas 45% had only older siblings, 33% had only younger siblings, and about 10% had both.
The most common microbes in the infants’ airways and guts included Firmicutes, Proteobacteria, Actinobacteria and Bacteroidetes. The researchers found that, especially in the first year of age, the presence of older siblings was among the most important factors to influence the composition of the airway and gut microbiota.
In their airways, children with older siblings had lower abundance of Firmicutes and higher levels of Proteobacteria at all sample times. Actinobacteria were more abundant at one and three months of age in infants with older siblings. Moraxella and Neisseria were more abundant in children with older siblings, whereas Staphylococcus was less abundant in those children, the team found.
In their guts, children with older siblings had higher abundances of Bifidobacterium and lower abundances of Clostridium in their first month of age. At one year, those children had lower levels of Veillonella and Enterobacteriaceae, including Escherichia/Shigella. The higher levels of Prevotella in children with older siblings was more pronounced at four years and persisted at six years, the researchers found.
Age gap
The age difference to the closest older sibling had the strongest influence, with smaller age gaps being associated with a more diverse gut microbiota and a less diverse airway microbiota. Instead, the number of older siblings did not have any effect on these microbial communities.
By six years of age, 7% of participating children developed asthma, about 6% developed allergic rhinitis and nearly 26% had a tendency towards allergic inflammation. The team found that the sibling signature in the gut microbiota at one year of age was linked to a decreased risk of asthma at six years. No associations were found for allergic sensitization and allergic rhinitis.
The most prominent development of the gut microbiota occurs within the first few years of life, the researchers note. “During this early maturation, it is plausible that the microbiota would be more likely to be influenced by other microbiotas on a not-too-distant level of maturity.”
Regardless of the mechanisms behind the results, their implications — especially in microbiota studies — should not be underestimated, the researchers say. “We suggest that the frequent stratification by number of siblings in microbiota-related studies should be reconsidered in favor of stratification by age gap to the closest sibling.”
