Leading to nearly one-half million deaths worldwide in 2019, asthma is a major non-communicable disease in all age groups. It is the most common chronic disease among children. Many factors have been linked to an increased risk of children developing asthma, although it is often difficult to find a single, direct cause.
Gut and lung microbiota present as relevant influences. Increased prevalence of asthma has been linked to reduced exposure to substances that promote immune system maturation. Because the maturation of innate and acquired immunity occurs mainly at the gut level, gut microbes are thought to play an important role in what is termed the “hygiene hypothesis.”
Recent research suggests a role for probiotics in rebalancing immune response, repairing dysbiosis, and mitigating airway inflammation in asthma.
Asthma, in brief
Asthma is a condition marked by chronic inflammation of the respiratory tract, reversible airflow limitation, and bronchial hyper-reactivity.
Inflammation and narrowing of the small airways in the lungs cause asthma symptoms, which can be any combination of cough, wheeze, shortness of breath, and chest tightness. Asthma symptoms can be made worse by common triggers: viral infections (colds), dust, smoke, fumes, changes in the weather, grass and tree pollen, animal fur and feathers, strong soaps, and perfume.
Factors linked to an increased risk of developing asthma include family incidence, having other allergic conditions, early life events (low birth weight, prematurity, exposure to tobacco smoke and other sources of air pollution, as well as viral respiratory infections), overweight and obesity, and exposure to a range of environmental allergens and irritants (house dust mites, molds, and occupational exposure to chemicals, fumes or dust.)
Asthma cannot be cured, but good management with inhaled medications (bronchodilators and/or steroids) can control the disease. In addition, biologics, such as blocking mediators of inflammation, may be indicated for severe asthma. However, access to these treatments is often limited in many low- and low-middle-income countries.
Rationale for probiotics in childhood asthma
The aforementioned “hygiene hypothesis” emerged because of the observation that allergic diseases such as asthma were more prevalent in affluent populations than in people exposed to less hygienic settings. Natural environments enrich the human microbiome, promote immune balance, and protect from allergy and inflammatory disorders. A decline in biodiversity may disturb the immune response and microbial balance.
Asthmatic children may present with dysbiosis of the intestinal and respiratory microbiome. Dysbiosis may promote the start of inflammatory pathways and pitch in bronchial obstruction and airway hyper-reactivity. Moreover, intestinal dysbiosis significantly affects asthma pathogenesis.
Commonly used drugs such as antibiotics may imbalance gut and lung microbiota. The dysregulation of the gut-lung axis contributes to allergic disorders.
Potential mechanisms of action by probiotics in asthma
Oral probiotics may be beneficial through various actions:
- Fortifying intestinal barrier
- Inhibiting the growth of pathogens
- Activating mucosal and innate immunity
- Activating anti-inflammatory processes
Reviews and meta-analyses of probiotics in asthma
Systematic reviews and meta-analyses of probiotics in asthma and allergic diseases have been conducted with various conclusions. Some observed no benefit while others saw benefits with specific strains. Therefore, analyzing the data concerning a single probiotic strain is necessary. Each strain may exert specific activities depending on its unique characteristics.
Individual studies with probiotics
The following double-blinded, placebo-controlled studies reported on specific probiotic products.
- Fermented milk containing Lacticaseibacillus casei: a study in 187 asthmatic preschoolers for one-year showed no effect.
- Lacticaseibacillus rhamnosus supplementation: a study in 131 at-risk infants for six months showed a reduced number of sensitizations both after six months and a further 6-month follow-up.
- Lactobacillus gasseri supplementation: a study for eight weeks in 105 asthmatic children reported enhanced bronchial function and diminished asthma.
- Limosilactobacillus reuteri supplementation: a study in 50 asthmatic children for two months showed dampened type-2 inflammation.
- A probiotic mixture containing specific strains of Bifidobacterium longum, Bifidobacterium infantis, and Bifidobacterium breve: a study in 40 children with seasonal allergic rhinitis and intermittent asthma for four weeks observed reduced respiratory symptoms and improved quality of life.
- A multi-strain synbiotic containing Lacticaseibacillus casei, Lacticaseibacillus rhamnosus, Streptococcus thermophilus, Bifidobacterium breve, Lactobacillus acidophilus, Bifidobacterium infantis, Lactobacillus delbrueckii subsp. bulgaricus, and fructooligosaccharides: a study in 72 asthmatic children for 60 days reported reduced viral respiratory infections, but only during the first month.
- A synbiotic compound containing Bifidobacterium infantis and fructooligosaccharides: a study in asthmatic children for six months reported a significant reduction in outpatient visits for asthma-related problems.
- A probiotic mixture containing specific strains of Ligilactobacillus salivarius and Bifidobacterium breve: Probiotics in Pediatric Asthma Management (PROPAM): study for 16 weeks in 446 children with asthma or wheezing reported that the probiotic mixture diminished the odds of having an acute respiratory episode to a third. The probiotic mixture reduced nearly a quarter of the likelihood of having two crises and halved the number of children with moderate to severe attacks.
In summary, these studies show considerable evidence that probiotic supplementation reduced asthma severity in children with pre-existing asthma.
Prevention has been less successful. A meta-analysis of 11 clinical trials concluded that probiotics supplementation in the first months after birth did not decrease the risk of asthma development in the first years of life in high-risk children.
Some findings do support the possibility that prenatal probiotics supplementation may prevent allergies and asthma, mostly in children at high risk of allergy development. However, the grade of evidence is still slight, and further studies are needed.
Based on the existing literature, oral probiotics may be beneficial in children with asthma. However, the duration of treatments, entities evaluated, strains used, and characteristics of enrolled subjects varied across studies. The choice of probiotics (strain-specific) should be based on documented evidence.
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Clare Fleishman, MS, RDN, bridges the gap between science and health across most platforms: major newspapers, magazines, books (Globesity), workshops, social media, and websites. In 2010, she launched www.ProbioticsNow.com to share the cascade of discoveries in the microbiome. Always amazed at this “forgotten organ” Fleishman also creates white papers, blogs, videos, and social media for the International Probiotics Association. In 2022, she published a book titled Fertility: Why Microbes, Weight & Nutrition Matter.
The International Probiotics Association (IPA) is a global non-profit organization bringing together through its membership, the probiotic sector’s stakeholders including but not limited to academia, scientists, health care professionals, consumers, industry, and regulators. The IPA’s mission is to promote the safe and efficacious use of probiotics throughout the world. Holding NGO status before Codex Alimentarius, the IPA is also recognized as the unified “Global Voice of Probiotics” around the world.
IPA disclaimer: Probiotics have diﬀerent characteristics, qualities and actions that are unique to the speciﬁc strain or combinations. The label should identify the genus, species and strain for each microorganism in the product (i.e. Lactobacillus acidophilus IPA001). If a claim pertaining to individual strains or a blend of strains contained in the product is made, the manufacturer should maintain evidence that the amount(s) provided in the product is consistent with the scientific evidence in support of the claim.