We systematically searched the WoSCC database, setting the search timeframe from the database’s inception to 2023, with the search completed on October 25, 2023. A total of 1364 articles were retrieved, and the selection process was finalized on October 27, 2023. The search strategy was as follows:

Two reviewers independently identified and discussed potential discrepancies in the data search, ultimately reaching a consensus. After excluding articles written in non-English and those whose titles and abstracts did not match the research content, and by restricting the publication type to reviews and original articles, we obtained 794 articles that met the criteria for inclusion in the analysis ( Figure 1 ).

This approach ensured a comprehensive and focused collection of relevant literature, providing a robust foundation for the subsequent bibliometric analysis.

The original data were extracted from WoSCC database, including paper and citation numbers, publication year, country/region, affiliation, authors, journals, references, and keywords. The data were imported into VOSviewer (version 1.6.19) and CiteSpace (version 6.2.R3) for subsequent bibliometric analysis.

The Web of Science (WoS) Core Collection database, known for its rigorous journal selection, has become internationally recognized for evaluating the scientific achievements of scholars and institutions and for assessing the development of disciplines (Sun et al., 2022). Therefore, our research chose the WoS database.

CiteSpace is a software tool for visualizing and analyzing academic literature citation networks. It automatically generates citation network graphs and calculates citation frequency, keyword distribution, collaboration among authors, and displays this information in visual charts. CiteSpace also offers a range of analysis tools, such as clustering analysis and keyword co-occurrence analysis, to help researchers identify important research themes, hotspots, and influential papers in academic fields (Synnestvedt et al., 2005).

Similar to CiteSpace, VOSviewer supports visualization analysis based on literature citation networks. Using VOSviewer, researchers can easily explore citation relationships between literature and research hotspots. It aids in quickly grasping an overview of large-scale literature data, assisting in identifying field hotspots, research trends, and relevant literature resources and research directions related to specific research questions (van Eck and Waltman, 2010; Pan et al., 2018). In the generated network graphs, nodes can represent different countries, institutions, authors, or keywords. The size of a node reflects the number of publications associated with it, while different colors represent different clusters or years. Lines between nodes reveal collaboration or citation relationships.

Python is an open-source programming language known for its flexibility and productivity. Compared to traditional data visualization tools, Python offers the availability of multiple plotting and graphics libraries and the customization of various types of advanced charts (Wang and Maniruzzaman, 2022). Our study utilized Python to extract multiple key attributes from the literature, such as publication year, authors, institutions, countries, research fields, journals, references, and author keywords, followed by comprehensive statistical analysis. To visually represent the data, we also created bubble charts illustrating the annual publication trends in various research fields, journals, and author keywords. In these charts, the diameter of a bubble symbolizes the most prominent research field, journal, or author keyword in a particular year, and the number inside the bubble indicates the corresponding number of publications (Sun et al., 2022).

Before initiating the bibliometric analysis, we meticulously processed the raw data using Python. Our data cleaning process involved several key steps:

These steps ensured the accuracy and consistency of our data, which is crucial for the integrity and reliability of our bibliometric analysis.

Figure 2 illustrates the trends in annual publication volume and citation frequency. The total number of articles surged from 3 in 2011 to 190 in 2022. Since 2011, lung and intestinal microbiota research has shown an upward trend. The annual publication volume exceeded 150 articles starting in 2021, indicating a continuous increase in the number of scholars conducting related research and a flourishing development of theories in lung and intestinal microbiota research.

Since the database’s inception, 5,710 authors have participated in lung and intestinal microbiota research, publishing a total of 794 articles. Table 1 displays the top 10 core authors, their publication count, total citations, and H-index. The top 10 authors published 63 articles collectively, totalling 1,750 citations. In terms of publication count, Jian Wang leads with 8 publications, followed by Derrick R Samuelson with 7 publications. Among them, 4,963 authors have published only one article, and only 23 have published five or more. Regarding total citations, Benjamin J Marsland leads with 2,522 citations, though outside the top 10 authors. Eva S Gollwitzer followed them with 2,120 citations and Aurelien Trompette with 2,052 citations. Regarding H-index, Valentin Sencio and Francois Trottein are in the leading positions. When assessing prolific authors, it is essential to consider the quantity of articles and the quality and publication timeline.

Among the top 10 authors in terms of publication volume, 5 are based in China, 3 in the United States, and 2 in France. This data indicates the concentration of research in this field in specific countries. VOSviewer software was used to depict the collaborations among authors in this field ( Figures 3 , 4 ). We set a threshold in the statistical analysis, requiring authors to have published at least 2 articles; ultimately, only 720 authors met this threshold. After removing unconnected nodes, 89 authors met the threshold. In the network visualization, the size of a node increases with the number of contributions by the author. The larger the node, the more articles the author has published.

1,431 institutions systematically published articles on the lung and intestinal microbiota. The majority of the top 10 institutions in terms of publication volume are from China. Zhejiang University in China ranks first in the number of publications and the H-index, with 26 publications, 878 total citations, and an H-index of 14. Fudan University is second with 18 publications, 297 total citations, and an H-index 8. Shanghai Jiao Tong University (17 publications, 470 total citations) and Sun Yat-sen University (17 publications, 310 total citations) are tied for third place ( Table 2 ).

Institutional collaboration analysis was conducted using VOSviewer software, and an institutional collaboration network map was constructed ( Figure 5 ). The minimum publication threshold was set to 5, with 66 institutions meeting this threshold. After removing unconnected nodes, 61 institutions met the criteria. As shown in Figure 5 , there is close collaboration among these institutions.

Our analysis included 57 countries. The top 10 countries/regions were ranked based on the total number of publications by all authors. China had the highest publication volume, accounting for 45.2%, followed by the United States (21.8%) and France (5.3%) ( Table 3 , Figure 6 ). Only China and the United States published more than 100 articles. Although China had the highest number of publications, the United States led in total citations and H-index, indicating a higher quality of articles. The United States maintained the most vital international collaboration partnerships with other countries in this field.

794 articles related to the lung and intestinal microbiota were published across 333 journals, as detailed in Table 4 . The journal with the most publications was Frontiers in Microbiology (39 articles, accounting for 4.9%), followed by Frontiers in Immunology (35 articles, 4.4%), Frontiers in Cellular and Infection Microbiology (23 articles, 2.9%), Plos One (21 articles, 2.6%), Nutrients (17 articles, 2.1%), Biomedicine & Pharmacotherapy (16 articles, 2.0%), Scientific Reports (15 articles, 1.9%), International Journal of Molecular Sciences (15 articles, 1.9%), Gut Microbes (13 articles, 1.6%), and Frontiers in Pharmacology (12 articles, 1.5%). Nature Medicine had the highest total citations (2004) but only published 3 articles.

Supplementary Figure 1 presents a bubble chart of the top 20 journals related to lung and intestinal microbiota research. The chart reveals that since 2021, Frontiers in Microbiology, Frontiers in Immunology, and Frontiers in Cellular and Infection Microbiology have been the most prolific journals in this research area. Plos One has maintained a steady publication volume since 2013, while Scientific Reports shows a general downward trend in publication volume. Specifically, Frontiers in Microbiology published 12 articles in this field in 2023.

The research on lung diseases and intestinal microbiota encompasses 64 fields, with Table 5 listing the top 20 fields in publication volume. The fields of “Microbiology” and “Immunology” lead in publication volume, with 166 and 144 papers, respectively, and rank highest in total citations, with 6483 and 5025 citations each. The field with the highest average citation number is “Virology” (109.5 citations per paper), which, despite having a smaller publication volume of only 10 papers, has garnered relatively high attention and citations.

Supplementary Figure 2 presents a bubble chart sorted by publication volume for the top 20 research fields. According to the chart, “Microbiology” and “Immunology” have been the most popular research fields since 2011. Since 2018, there has been a rising trend in the publication volume in fields such as “Pharmacology & Pharmacy,” “Oncology,” “Biochemistry & Molecular Biology,” “Respiratory System,” “Medicine, Research & Experimental,” “Multidisciplinary Sciences,” and “Cell Biology.” This trend indicates increasing attention in these areas.

An analysis was conducted on 1,046 author keywords, with “intestinal microbiota/microbiome,” “microbiota/microbiome,” and “gut-lung axis” being the keywords that appeared over 100 times ( Table 6 ). As shown in the bubble chart of Supplementary Figure 3 , since the outbreak of COVID-19/SARS-CoV-2 in 2020, it has become a focal point of interest.

Using CiteSpace software, the keywords were categorized into 11 clusters ( Figure 7 ). Closely related keywords were automatically grouped into a cluster, with each cluster named after the keyword with the highest log-likelihood ratio (LLR). The higher the LLR, the more representative the keyword is of its cluster. The 11 clusters identified in this field are #0 asthma, #1 probiotics, #2 non-small cell lung cancer, #3 inflammation, #4 metagenomics, #5 COPD, #6 immunity, #7 gut, #8 pulmonary hypertension, #9 gut-lung axis, and #10 sepsis, with cluster #0 being the largest.

A timeline chart was created based on the first year of the appearance of the keywords ( Figure 8 ). In this field, the earliest active cluster was #9, followed by the rise of #1. Our study identified 5 keywords with the most potent citation bursts ( Figure 9 ), including asthma, lung, airway hyperresponsiveness, allergy, and non-small cell lung cancer.

Figure 10 displays a network visualization map of cited references, with yellow nodes representing the most recently appearing keywords, indicating these are the latest cited references in the field. Figure 11 shows 12 related clusters identified by CiteSpace: COVID-19/SARS-CoV-2, COPD, chronic pulmonary disease, immunotherapy, asthma, sepsis, tuberculosis, lung cancer, cystic fibrosis, anti-tuberculosis therapy, pulmonary hypertension, and Th1 and M1 polarization.

A burst strength analysis of the references was conducted using CiteSpace to gain a comprehensive understanding of the cited references. The time frame was set from 2011 to 2023, with a one-year interval, and 40 references with significant burst strength were identified. Among these, 8 references had a burst strength more significant than 10 ( Figure 12 ). This analysis highlights the most influential and rapidly emerging topics in the field within the specified time frame.

In this study, we analyzed 794 articles from the WoSCC database in the field of lung diseases and intestinal microbiota using Python, VOSviewer, and CiteSpace. The research findings indicate a significant increase in annual publications and citation numbers starting from 2020, with a predominant contribution from China. This highlights the extensive research contributions of China in this field. Among the top 10 institutions in terms of publications, 9 are from China, including Zhejiang University, Fudan University, Shanghai Jiao Tong University, Sun Yat-sen University, Capital Medical University, Beijing University of Traditional Chinese Medicine, Chinese Academy of Sciences, Guangzhou Medical University, and Southeast University. This indicates increasing attention and emphasis on this research area in China.

In terms of publication volume, the most prolific author is Jian Wang from China. However, in terms of total citations, Benjamin J Marsland from Monash University, Australia, holds the leading position but is outside the top 10 authors. Following him are Eva S Gollwitzer from Universitaire Vaudois, Switzerland, and Aurelien Trompette. In terms of the H-index, the leading positions are occupied by Valentin Sencio and Francois Trottein. When assessing prolific authors, it is crucial to consider the quantity of their publications and the quality of the articles.

From the perspective of journals, Frontiers in Microbiology holds a leading position as the journal with the highest number of publications in this field. However, Nature Medicine has the highest total citations despite publishing only three articles. This discrepancy highlights the significant impact and high quality of the articles in Nature Medicine.

The most focused research fields are “Microbiology” and “Immunology”, which lead in both the number of publications and total citations. Despite having fewer publications, the field of “Virology” has the highest average citation count. This heightened attention and citation rate could be related to the outbreak of COVID-19/SARS-CoV-2 in 2020, which has also become a focal point of interest.

Benjamin J Marsland from Monash University is a prominent author in terms of citations in this field. His long-term research into the impact of the microbiome on human immunity and the respiratory system has been influential. His team discovered a new protective pathway within the gut-lung axis - L-tyrosine–PCS, which can be used to treat or prevent inflammatory diseases (Wypych et al., 2021). This discovery underscores the critical interplay between intestinal microbiota and lung health, revealing novel pathways for therapeutic interventions.

The lung and intestinal microbiota fields have consistently attracted attention from scholars worldwide. Current research hotspots, identified through analyses of the most-cited references, keyword co-occurrence, clustering, and emerging trends, primarily focus on the gut-lung axis, probiotics, COVID-19, asthma, and COPD. It is well-recognized that intestinal microbiota dysbiosis is associated with increased susceptibility to respiratory diseases and alterations in lung immune responses and homeostasis. Although an increasing number of epidemiological and experimental studies have highlighted the relationship between the intestinal microbiome and the lungs, referred to as the “gut-lung axis” (Bingula et al., 2017; Dang and Marsland, 2019), the mechanisms by which intestinal microbiota influence lung diseases remain unclear (Budden et al., 2017). Understanding these mechanisms is crucial for developing effective treatments and prevention strategies for respiratory diseases influenced by intestinal microbiota.

The gut-lung axis is an emerging field with many aspects yet to be fully understood. Future research aims to delve deeper into understanding the gut microbiota and its metabolic products, airway microbiota and their metabolites, and to develop suitable bioinformatics and machine learning models. These models are intended to predict and assess various gut-lung axis diseases and health statuses, leading to the development of personalized prevention and treatment strategies (Zheng et al., 2020; Zheng et al., 2023; Liang et al., 2022). Recent discoveries indicate significant differences in the gut microbiota of lung cancer patients compared to their lung microbiome communities. Changes in the gut microbiota can affect the prognosis and treatment outcomes of lung cancer (Goto, 2022; Tsay et al., 2021; Tsay et al., 2018), making the role of the gut-lung axis in the prevention, diagnosis, and treatment of lung cancer a valuable area of exploration. Dietary habits have been found to influence the gut microbiota, thereby impacting the prevention and treatment of lung diseases (Gasmi et al., 2021; Healy et al., 2021). Understanding the relationship between nutrition and the gut-lung axis, and designing specific dietary plans, may be one of the future research directions. COVID-19, one of the most widely discussed diseases in recent years, has been shown to be influenced by the gut microbiota, which may affect the host’s infection and immune response to the virus (Wang H. et al., 2021; McGinniss and Collman, 2021; Liu et al., 2022; Ancona et al., 2023). Therefore, studying the relationship between the gut-lung axis and COVID-19 is of significant importance for the prevention and treatment of this disease. This line of research holds the potential to unlock new insights into managing not only COVID-19 but also other respiratory diseases influenced by the complex interactions within the gut-lung axis.

Our study leveraged bibliometric methods to perform a visual analysis of research on the relationship between intestinal microbiota and lung diseases, aiding scholars in better understanding the hotspots and trends in this field. However, our study also has limitations. We analyzed only articles published on WoSCC within a specific timeframe and in English, potentially overlooking research results from other databases. Despite this, using visual methods to understand the current state, hotspots, and trends in a field remains valuable.