Recent preclinical evidence pinpoints a critical window early in life where gut microbial changes (dysbiosis) are most influential in experimental asthma.
Asthma, the basics
Asthma is an episodic or chronic airway inflammatory disease characterized by reversible airflow restriction and bronchial hyperresponsiveness. Implicated factors in asthma pathogenesis include genetic and epigenetic factors, environmental exposure to indoor and outdoor substances as well as microbial dysbiosis.
According to the “hygiene hypothesis,” early-life exposure to specific microbiota components is crucial for the maturity of the immune system; their absence may increase the susceptibility to asthma. Notably, microbes are important immunomodulators, spawning regulatory T cells, which can suppress inflammation. This anti-inflammatory effect is thought by researchers to be a possible mechanism for the benefit of probiotics in asthma.
Differences in asthmatics and healthy controls
The gut microbiota is different in asthmatic individuals compared to healthy controls, according to recent studies described below and points to the existence of a gut-lung axis.
- Low microbial diversity in early life is linked to asthma.
- Also, microbial diversity was lower in formula-fed infants than in breastfed infants in one study. (However, the significance of breastfeeding in asthma prevention is not consistently demonstrated.)
Specific gut bacteria, the studies
- Clostridium and Eggerthella lenta were more abundant in the gut of asthmatic patients than in that of healthy controls in a 2018 study.
- A decrease in Bifidobacterium, Akkermansia, and Faecalibacterium abundances and the increase in Candida and Rhodotorula abundances increased a child’s risk of developing allergies and asthma.
- Gut colonization by Clostridium difficile at 1 month of age was associated with asthma at 6-7 years of age.
Gut microbiota modification
Could altering the gut microbiota modulate pulmonary immune response as well as prevent and/or treat asthma?
- After noting reductions in Lachnospira, Veillonella, Faecalibacterium, and Rothia abundances in the gut of asthmatic infants, researchers inoculated germ-free mice with these bacteria. Results showed ameliorated airway inflammation and prevention of asthma development.
- In both rodent and human studies, strains of Lactobacillus rhamnosus, Lactobacillus casei, and Bifidobacterium breve potentially prevented and treated allergies and asthma.
- Lactobacillus strains reduced asthma severity and improved asthma control in a trial of 160 asthmatic children.
Importantly, not all studies show a clear benefit of probiotics in asthma.
A meta-analysis published in 2018 reviewed the effects of probiotics supplementation in pooled data from 11 studies with 910 asthmatic children. The proportion of children with fewer episodes of asthma was significantly higher in the probiotics group than in the control group but “no statistical significance was observed in childhood asthma control test, asthmatic symptom in the day and night, the number of symptom-free days, forced expiratory volume in the first second predicted and peak expiratory flow.”
The meta-analysis did neither confirm nor rule out the beneficial effects of probiotics supplementation in children with asthma. More well designed trials with larger sample sizes should be conducted.
Gut microbiota dysbiosis is associated with an increased risk and severity of asthma, suggesting that appropriate gut microbiota modifications may be a feasible way to prevent and treat asthma.
However, research shows that the effect of probiotics in asthmatics varies. Strain is crucial because impact varies by strain; each probiotic strain is a unique organism, quite different from even closely related strains.
Arrieta, Marie-Claire et al. “Early infancy microbial and metabolic alterations affect risk of childhood asthma.” Science translational medicine vol. 7,307 (2015): 307ra152. doi:10.1126/scitranslmed.aab2271
Cevhertas, Lacin et al. “Advances and Recent Developments in Asthma in 2020.” Allergy, 10.1111/all.14607. 30 Sep. 2020, doi:10.1111/all.14607
Chunxi, Li et al. “The Gut Microbiota and Respiratory Diseases: New Evidence.” Journal of immunology research vol. 2020 2340670. 31 Jul. 2020, doi:10.1155/2020/2340670
Lin, Jilei et al. “Probiotics supplementation in children with asthma: A systematic review and meta-analysis.” Journal of paediatrics and child health vol. 54,9 (2018): 953-961. doi:10.1111/jpc.14126