Asthma, an inflammatory disease that restricts the airways and causes breathlessness, is a major global public health concern (1). Poorly managed asthma negatively impacts quality of life and increases the risk of premature death, particularly in children and adolescents (1). Current thought associates the development of asthma with numerous environmental exposures, which spark immune responses that are, themselves, shaped by both internal and external factors, including the microbes that live within the gut (1). Ultimately, the development of asthma is complex and multifactorial, however one area of research is gaining traction, and that is the role that the gut microbiome may play in the onset of childhood asthma (1).

The Gut Microbiome in Early Years

Within the first couple of years of life, the composition of the infant microbiome matures, helping to shape the way the immune system develops (2). During that first year, the composition shifts rapidly, greatly influenced by the surrounding environment (3). These first years of life are crucial for potential sensitivity to environmental exposures and immune function (2). Disturbances of the microbiome during this time may influence the likelihood of a child developing asthma, allergies, and other immune-related disorders (2).

Influences on Microbiome Composition in the First Year of Life

Numerous factors, many of them modifiable, influence the way in which the infant’s gut microbiome matures and populates itself, with the potential for long-lasting impact on the composition of the microbiome, and the child’s future health (2). 

The main factors of influence on microbiome population and composition are:

• Mode of delivery – Caesarean compared to vaginal birth.
• Antibiotic use – maternal use during birth, and infant use in first year.
• Feeding method – Breast milk versus formula.
• Gestational age – Full-term versus premature birth.
• Birth Order – Older siblings are more likely to have less diverse gut microbiomes.
• Introduction of solid foods – This prompts the largest shift in gut microbiome composition.
• Environmental exposures – e.g. farms, animals all have their own unique microbial fingerprint (2, 3, 4).

Research on Gut Microbiome and Asthma Development

A delay or alteration in the establishment of microbial groups can lead to an ‘immature’ gut microbiome, which has been linked with an increased risk of asthma later on in life (4). 

A 2018 study on 700 children found that a lack of maturation of the gut microbiome of a child at one year of age was associated with an increased prevalence of asthma at the age of five (2). Interestingly, this link was only found in children of asthmatic mothers, which suggests that the environment and subsequent microbiome composition may act like an ‘on switch’ in pre-disposed children (2). In this study, the most significant determinant of a ‘mature’ gut microbiome at age one was having an older sibling (2).

Another study found that colonisation by Clostridium difficile in the gut microbiome at one month of age was associated with wheeze in the first six to seven years of life, and asthma at six to seven years (5). Clostridium difficile colonisation was influenced by mode and place of delivery (5).

Strategies for Asthma Prevention

These results suggest that an awareness of environmental influences on the gut microbiome in the first year of life may play an important preventative role in reducing the likelihood of a predisposed child developing asthma, when the gut microbiome is highly malleable and able to be manipulated (2).

Probiotics, prebiotics, and synbiotics are currently being researched for their ability to restore balance in the gut microbiome (4). Although promising, there is not enough conclusive evidence to make these an official recommendation to prevent or treat asthma (4). There is also a growing body of evidence suggesting that the use of prebiotics and probiotics during pregnancy may influence the developing fetal immune system, reducing the risk of them developing asthma. (6) Overall, manipulation of the gut microbiome to prevent and possibly treat asthma shows promise as a novel therapeutic option for susceptible children (7).