Gut bacteria and lung injury research has exploded since 2019, a decade-long analysis reveals

The human gut is home to trillions of microbes whose collective genetic repertoire dwarfs our own genome by more than 150-fold, and over the past decade scientists have become increasingly convinced that this inner ecosystem does not stop at the intestines. It reaches, through blood, immune cells and nerves, all the way into the lungs. A new bibliometric study published in Frontiers in Medicine has now mapped the entire research landscape connecting gut microbiota to lung injury, and the picture it paints is one of a field that has shifted from quiet obscurity to explosive growth, driven largely by laboratories in China and still awaiting its decisive translation into human clinical practice.

The analysis, led by Xinru Wu and Tiancheng Yu with colleagues at Kunshan Integrated TCM and Western Medicine Hospital, Nanjing Tech University, Jiangsu Normal University and collaborating institutions, drew on two of the largest literature databases in science: the Web of Science Core Collection and Scopus. Searching from January 2015 to a cutoff of May 25, 2026, the team retrieved 702 qualifying articles from Web of Science and 334 from Scopus, restricting results to original research articles and reviews in English. They then processed this corpus with a suite of visualization tools — VOSviewer for collaboration and co-occurrence networks, CiteSpace for citation bursts, and the Bibliometrix package in R for knowledge maps — to reveal where the field has been and where it is heading.

The headline finding is a dramatic inflection point in publication output. Output remained modest between 2015 and 2018, with small year-to-year fluctuations, before entering a phase of rapid and sustained growth after 2019. Web of Science output peaked at 133 articles in 2025, while Scopus recorded 74 that year. The authors attribute the surge to several converging forces: the maturing of the gut-lung axis framework, the broad adoption of high-throughput sequencing and multi-omics technologies, and heightened interest in host-microbiome interactions during and after the COVID-19 pandemic. The apparently low numbers for 2026 simply reflect the partial-year search window rather than any slowdown.

Geographically, the field is strikingly concentrated. China led global output with 483 Web of Science publications — roughly 69 percent of the dataset — followed by the United States with 79. The pattern held in Scopus, where China accounted for 265 of 334 articles. At the institutional level, Fudan University topped both databases and emerged as the core hub of the collaboration network. Yet the study also flagged a notable weakness: international collaboration remains thin. Only about 5 to 6 percent of Chinese publications involved co-authors from multiple countries, compared with 19 to 32 percent for the United States, suggesting that despite China’s dominance in volume, the field’s collaborative fabric is still being woven.

Journal analysis revealed Frontiers in Immunology as the field’s central publication and citation hub, with 34 articles and 1,165 citations in the Web of Science dataset. Other productive outlets included Frontiers in Microbiology, Frontiers in Pharmacology, Journal of Ethnopharmacology and Frontiers in Cellular and Infection Microbiology, while highly cited nodes extended to PLoS ONE, Nature, the American Journal of Respiratory and Critical Care Medicine and Gut. The most influential individual papers spanned a remarkable range: a Science study on the microbial metabolite desaminotyrosine protecting against influenza through type I interferon signaling, a Nature Immunology paper on innate immune responses to trauma, and work on how gut microbiota modulates LPS-induced acute lung injury via the TLR4/NF-κB pathway. Citation-burst detection highlighted the strongest surges around papers on microbiota and the gut-lung axis, host defense against pneumococcal pneumonia, and, most recently, gut-lung crosstalk in sepsis-induced lung injury and microbiota-derived succinate aggravating injury after intestinal ischemia-reperfusion.

Keyword clustering distilled the field into a handful of coherent themes. Inflammation was the most frequent keyword, followed by microbiota, the gut-lung axis, mouse models and sepsis. The clusters pointed to gut-lung axis-mediated immune regulation, oxidative stress and inflammatory signaling, the protective functions of short-chain fatty acids, sepsis and critical illness-related injury, environmental exposure-induced microecological imbalance, and targeted interventions using probiotics and dietary strategies. Thematic evolution analysis showed a clear trajectory: early work from roughly 2017 to 2020 focused on intestinal permeability, mesenteric lymph and bacterial translocation; the middle phase from 2021 to 2023 shifted to dysbiosis and inflammatory pathway activation; and studies from 2024 onward have moved toward macrophage polarization, aryl hydrocarbon receptor-mediated immunometabolism, high-throughput sequencing and the hunt for clinical diagnostic biomarkers for acute respiratory distress syndrome.

The scientific rationale underlying this boom is compelling. Acute lung injury and its severe form, ARDS, affect roughly 86 people per 100,000 globally each year, and severe cases still carry mortality rates of 40 to 50 percent. Sepsis accounts for more than 60 percent of cases, and current treatments — lung-protective ventilation, fluid management, anti-infection therapy and glucocorticoids — remain largely supportive, with no drugs that specifically interrupt the core pathological cascade. Against this backdrop, the gut-lung axis offers an entirely new therapeutic entry point. Through the axis, gut microbes and their metabolites reach the circulation, immune cells migrate between mucosal sites, vagal signals travel between the organs, and, when the gut barrier fails, bacteria and their toxins translocate into the bloodstream.

Mechanistically, the field has converged on three hotspots. The first concerns how gut microbiota shapes the pulmonary immune microenvironment: intestinal CD103-positive dendritic cells secrete retinoic acid, programming lymphocytes with homing receptors that guide them to bronchus-associated lymphoid tissue and the alveolar interstitium, where they secrete IgA, interferon-gamma and interleukin-17, while gut-derived regulatory T cells produce IL-10 and TGF-beta to restrain excessive inflammation. When dysbiosis breaches the epithelial barrier, lipopolysaccharide enters the circulation, activates TLR4 and fans systemic inflammation that lands in the lungs. The second hotspot centers on short-chain fatty acids — acetate, propionate and butyrate produced by fiber fermentation — which dampen NF-κB and MAPK signaling through G protein-coupled receptors and histone deacetylase inhibition, push alveolar macrophages toward reparative M2 phenotypes, strengthen tight junctions via ZO-1 and occludin, protect the alveolar-capillary barrier, activate the Nrf2 antioxidant pathway and even slow pulmonary fibrosis by suppressing TGF-beta1/Smad signaling. The third involves microecological interventions, from Lactobacillus and Bifidobacterium strains that rebalance macrophage polarization to traditional Chinese medicine compounds such as ruscogenin and 8β-hydroxy-α-cyclocostunolide, whose mechanisms the authors note align strikingly with the ancient TCM principle that the lung and large intestine are interior-exterior related.

Clinical evidence is beginning to back the preclinical enthusiasm. Patients with ALI and ARDS consistently show severe gut dysbiosis — reduced microbial diversity, a shifted Firmicutes/Bacteroidetes ratio, depleted beneficial Bifidobacterium and Lactobacillus, and overgrowth of opportunists such as Escherichia coli — and the degree of dysbiosis correlates with oxygenation indices, inflammatory markers, ventilation duration and 28-day mortality. During the COVID-19 pandemic, certain probiotic strains were reported to reduce nasopharyngeal viral load and pulmonary inflammatory infiltration. Yet the bibliometric keyword analysis exposed the field’s central weakness: terms like nonhuman, animals, mouse model and animal experiment dominate the literature, particularly in the Scopus dataset where they topped the frequency tables.

The authors are candid about this gap. The principal deficit, they conclude, is not a shortage of candidate mechanisms but the limited validation of strain-specific, metabolite-specific and dose-dependent effects in standardized human studies. Probiotic efficacy varies by strain and dose, unified clinical criteria are lacking, and different causes of lung injury may demand individualized microbial strategies. They also acknowledge the limitations of their own approach — only two databases, English-language literature and restricted document types — which may bias trends and rankings. Still, the study offers researchers a clear map: the field has built its mechanistic foundations in animals, and the next decade’s challenge, the authors argue, lies in large-scale, multicenter randomized controlled trials, multi-omics biomarker discovery, and the careful translation of gut-lung axis science into precision interventions for the intensive care units where lung injury claims so many lives.

Subject of Research: Bibliometric mapping of gut microbiota and lung injury research from 2015 to 2026

Article Title: Research progress and trends of gut microbiota and lung injury: a bibliometric and visualization analysis based on two databases (2015–2026)

Article References: Wu, X., Yu, T., Hu, S., & Zhang, T. (2026). Research progress and trends of gut microbiota and lung injury: a bibliometric and visualization analysis based on two databases (2015–2026). Frontiers in Medicine, 13, Article 1902880. https://doi.org/10.3389/fmed.2026.1902880

Image Credits: AI Generated

DOI: 10.3389/fmed.2026.1902880

Keywords: gut microbiota, gut-lung axis, lung injury, acute respiratory distress syndrome, bibliometrics, short-chain fatty acids, probiotics, sepsis, traditional Chinese medicine, pulmonary immunity, inflammation, microbiome