Respiratory diseases like obstructive sleep apnea (OSA), asthma, and chronic obstructive pulmonary disease (COPD) continue to contribute to global morbidity and mortality worldwide. In a recent article published in the MDPI journal Microorganisms, researchers review the role of the gut microbiome in these respiratory diseases and how modulating these bacterial species within the body could provide therapeutic benefits to mitigate these conditions.

Oral supplements

Several in vivo mouse studies have evaluated how incorporating specific dietary components may impact immune responses in the lungs. For example, a high fiber diet that increased circulating SCFA levels protected mice against allergic airway disease, whereas the inoculation of Lactobacillus johnsonii in the guts of mice reduced their Th2 response in the lungs.

Furthermore, supplementation with Bifidobacterium lactis BB-12, docosahexaenoic acid, as well as vitamins C and E effectively reduced lung inflammation in mice previously exposed to air pollution. Lactobacillus rhamnosus and Bifidobacterium breve probiotic supplementation in mice have also reduced airway inflammation and damage to the alveoli.

The effects of various oral supplements have also been evaluated in numerous human trials. For example, Bifidobacterium long BB536 supplementation in children between the ages of two and six years old effectively reduced the duration of common upper respiratory tract infections (URTIs) in this population. Similarly, supplementation with Lactobacillus Plantarum DR7 for 12 weeks significantly reduced nasal symptoms, the frequency of URTIs, as well as plasma levels of various pro-inflammatory markers, including interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF-α).

Fecal microbiota transplantation (FMT)

Researchers have also proposed FMT as a novel approach to re-establishing gut flora in patients with certain respiratory diseases. In experimental studies, mice subjected to FMT and subsequently provided a high-fiber diet exhibited an increased abundance of Bacteroidaceae and Lachnospiraceae, which was accompanied by a reduced likelihood of the mice experiencing severe symptoms associated with COPD. 

In another study assessing the impact of FMT on LPS-induced lung injury, downregulation of TLR4/NK-kB signaling was observed, along with reduced inflammation and oxidative stress in the lungs of animals with acute lung injury. Similar results were observed in another study, wherein FMT improved the response of germ-free mice following bacterial infection.

Despite these observations, more work is needed to determine the safety of FMT and the benefits associated with this treatment for respiratory diseases.