Background

Complementary and alternative medicine is generally defined as a group of diverse medical and healthcare interventions, practices, products or disciplines that are not considered as part of conventional medicine [1]. Specifically, the National Center for Complementary and Integrative Health (NCCIH) defines “complementary” medicine as a non-mainstream practice used together with conventional medicine, whereas “alternative” medicine refers to a non-mainstream practice used in place of conventional medicine [2]. In contrast, “integrative health” is defined as the coordinated delivery of conventional and complementary approaches together [2]. These three words – complementary, alternative, and integrative – comprise the most common ways to refer to these types of therapies [3], in additional to “traditional medicine” which has been defined by the World Health Organization as “the sum total of the knowledge, skill and practices based on the theories, beliefs and experiences indigenous to different cultures, whether explicable or not, used in the maintenance of health as well as in the prevention, diagnosis, improvement or treatment of physical and mental illness” [4]. For the purpose of the present study, these therapies will be referred to collectively as “traditional, complementary, alternative and integrative medicine” or “TCAIMs” hereafter. At present, a lack of consensus exists regarding how to categorize TCAIMs; in fact, by definition every therapy that falls under the umbrella of “TCAIM” exists as a result of being considered outside of the purview of conventional Western medical practices [3]. Therefore, one TCAIM therapy can be highly unrelated to another due to the fact that each originates from a different region in the world, culture, system of traditional medicine, and school of thought [4, 5]. Despite these challenges, attempts have been made to categorize TCAIMs. For example, the NCCIH divides TCAIM therapies into two main types: 1) natural products and 2) mind and body practices. Within the former category, they include therapies such as herbs, vitamins and minerals, and probiotics, while in the latter, they include therapies such as yoga, chiropractic and osteopathic manipulation, and meditation, as well as acupuncture, relaxation techniques, tai chi, qi gong, and hypnotherapy, among others [2]. Despite these efforts, the NCCIH has stated, however, that some TCAIMs may not fit neatly into either of these two groups, citing many systems of TCAIM including practices of traditional healers, Ayurvedic medicine, traditional Chinese medicine, homeopathy, naturopathy, and functional medicine [2].

Regardless of how TCAIMs are categorized, these therapies are perceived to be of value by their proponents for their emphasis on a holistic, patient-focused approach to healthcare, which include mental, emotional, functional, spiritual, economic, and social aspects [2, 6]. TCAIM is widely used around the world, with 88% of World Health Organization member states acknowledging their use, which by definition means that these 170 countries have formally developed policies, laws, regulations, programs and offices for TCAIM [4]. The prevalence of TCAIM use is high in many Western countries; for example, it is estimated that around 80% of Canadians have used TCAIM [7]. The prevalence of TCAIM use is also documented to be high among certain patient populations; in cancer patients, as many as 90% report using some type of TCAIM [8,9,10]. TCAIM is used by these patients for a variety of reasons, including symptom relief, improved quality of life, supplementing conventional therapy, supporting one’s philosophical orientations toward health, and achieving a sense of control over one’s care [11,12,13]. Integrative medicine (the use of complementary and conventional therapies) is becoming increasingly popular among patients and practitioners [14, 15], and sub-specializations of integrative care for specific diseases/conditions have also been established, such as integrative oncology [16, 17].

While some TCAIMs, such as meditation and yoga [18, 19], have undergone more thorough testing and have been found to be generally safe and effective, others have not been adequately researched to determine their effectiveness, and some have been found to be potentially harmful or interact negatively with conventional medicines [20,21,22]. The belief among patients that “natural means safe and better” [23] is well-documented, however, evidence from the research literature suggests otherwise. Many herbal and dietary supplements can be harmful when taken in large quantities. Certain weight loss and bodybuilding supplements have been shown to cause hepatotoxicity or even hepatic failure at therapeutic doses [24]. Furthermore, systemized pharmacovigilance of TCAIMs is poorly coordinated on a national and international level, and TCAIM therapies are generally not held to the same standards of regulation as that of pharmaceutical medicines in terms of quality, effectiveness, and safety [20].

The increase in popularity and prevalence of TCAIM use among patients, and growing acknowledgement among conventional healthcare providers that a need exists to approach TCAIM therapies, their traditions, and their practitioners with respect, are among some of the reasons for an increase in TCAIM research productivity which has resulted in a growth in the volume of the published literature over the past few decades [25,26,27]. The application of a research method known as a bibliometric analysis can facilitate a better understanding of a given field, such as that of TCAIM. A bibliometric analysis involves the statistical assessment of scientific publications, to identify the characteristics and determine the impact of the literature published in a specific academic discipline [28,29,30]. This increased interest in TCAIM research has led to the establishment and indexing of multiple TCAIM journals. While a number of bibliometric analyses have made attempts to evaluate the characteristics of all publications published in the area of traditional, complementary, alternative, and/or integrative medicine through the use of various search strategies [31,32,33,34,35], no study has comprehensively assessed the characteristics of the publications found within these source titles to date. Thus, the purpose of the present study is to provide current insight into the characteristics of publications published across TCAIM journals through a bibliometric analysis.

Methods

Publication search and characteristics

The 2021 Scopus Source List [36] was downloaded, and all Scopus-indexed journals belonging to the “complementary and alternative medicine” category (code 2707) were identified based on the All Science Journal Classification (ASJC). A single search containing the International Standard Serial Numbers (ISSNs) of all of these journals was run on Scopus on April 17, 2021; the search strategy can be found in Table 1. Search results were exported on the same day to prevent discrepancies between daily database updates. Searches were only conducted on Scopus because it is the largest abstract and citation database of peer-reviewed literature [37]; in comparison, Web of Science contains considerably fewer TCAIM-categorized journals, while OVID databases do not provide certain metrics such as publication citation counts [38]. All publication types were included, and no further search limits were applied. The following bibliometric data were collected: number of publications (in total and per year), authors and journals; open access status; journals publishing the highest volume of literature and their impact factors; language, countries, institutional affiliations, and funding sponsors of publications; most productive authors; and highest-cited publications. Trends associated with this subset of publications were identified and presented. Bibliometric networks were constructed and visualized using the software tool VOSviewer (version 1.6.16) [39, 40]. All aforementioned steps were conducted by a single author (JYN).

Table 1 Scopus Search Strategy Executed on April 17, 2021
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Bibliometric indicators of production

Relative growth rates and doubling times were calculated for publications published between 1938 and 2020. The relative growth rate represents the increase in the number of publications published per unit of time. The relative growth rate was calculated based on the following equation: [Relative Growth Rate = (logeW2 - logeW1)/(T2 - T1)], where loge W1 represents the log of initial number of articles, and loge W2 represents the log of final number of articles after a specific period of interval. T2-T1 represents the unit difference between the initial time and the final time. Doubling time is defined as the amount of time required for the subject matter to double its production. The doubling time was calculated based on the following equation: [DT = 0.693/Relative Growth Rate]. Price’s law was also applied to the subset of publications analysed [41]. This law proposes that the growth of scientific production follows an exponential function, and represents one of the most common indicators used to analyse productivity in a specific discipline or subset of publications. To assess whether the increase in data conforms to Price’s law of exponential growth, we carried out a linear adjustment of the values and another adjustment to an exponential curve.

Results

A total of 172,466 publications (42,331 open access), were published by 219,680 unique authors in 143 journals from 1938 to 2021. Since the 1940s, an upward trend with respect to the volume of publications can be observed, with a steep increase observed between the mid-2000s and mid-2010s. This upward trend has continued with 2020 marking the year with the highest number of publications to date. The Journal of Natural Products (n = 15,144) published the largest number of publications indexed in Scopus, followed by Zhongguo Zhongyao Zazhi (n = 14,577), and Planta Medica (n = 10,793). All journals included within this bibliometric analysis were hand-searched on InCites Journal Citation Reports [42]. As of 2020, 83 journals were still active (57.6%), of which 35 had a 2019 impact factor (range from 0.200 to 5.487). Table 2 provides complete details of the journals included in this bibliometric analysis, including the journal name, ISSN, whether the journal is active or inactive (as of 2020), coverage period, title history indication, publisher name, number of publications indexed in Scopus, and the 2019 impact factor (if available).

Table 2 Characteristics of TCAIM Journals Indexed in Scopus (n = 143)
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The subject area containing the largest number of publications was medicine (n = 172,456), followed by pharmacology, toxicology and pharmaceutics (n = 86,902), then biochemistry, genetics and molecular biology (n = 40,262). Publications were primarily published in English (n = 135,718), followed by Chinese (n = 24,614), then German (n = 8611). The most common document types were article (n = 139,540) and review (n = 13,418); articles primarily include original research, while reviews include literature, scoping, and systematic reviews. The most productive countries included China (n = 45,860), the United States (n = 29,523), and Germany (n = 10,120). The most common affiliations were the China Academy of Chinese Medical Sciences (n = 3560), the Beijing University of Chinese Medicine (n = 2896), and the Chinese Academy of Sciences (n = 2896); the most common funding sponsors were the National Natural Science Foundation of China (n = 5711), the National Institutes of Health (n = 4055), and the US Department of Health and Human Services (n = 4032). The general characteristics of eligible publications are summarized in Table 3. In addition, the 100 most highly published authors are provided in Table 4, and the 100 highest-cited publications are provided in Table 5.

Table 3 General Characteristics of Publications in TCAIM Journals
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Table 4 100 Most Productive Authors Across Publications in TCAIM Journals
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Table 5 100 Highest-Cited Publications in TCAIM Journals
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Figure 1 depicts the number of publications published per year from 1938 to 2020, inclusive of an exponential and linear curve. Mathematical adjustment to an exponential curve (y = 30.699e0.073x), as shown in this figure, resulted in a correlation coefficient r = 0.9698, which indicates that 5.94% of variability remains unexplained by this adjustment. In contrast, the linear adjustment (y = 97.915x - 1971.9) of the measured values provides an r = 0.8160, and thus an unexplained variability of 33.42%. These results suggest fulfilment of Price’s Law, with scientific production within CAIM journals showing exponential growth. Additionally, the relative growth rate was found to range from 0.05 to 0.67. Doubling time was found to range from 1.04 to 15.02. Table 6 provides annual relative growth rates and doubling times.

Fig. 1
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Number of Publications in Scopus-Indexed TCAIM Journals per Year from 1938 to 2020

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Table 6 Relative Growth Rates and Doubling Times
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Bibliometric networks were constructed and visualized using the software tool VOSviewer, and include all 172,466 captured by the present study’s search. This added layer of analysis of the most influential subset of publications captured provides a greater understanding of the relationship that exists between certain items (i.e. countries, keywords, authors, journals, etc.). In each bibliometric network (figure), each item is represented in a network visualisation by a label and a circle; the weight of an item determines the size of the label and the circle of an item. Figure 2 depicts a co-authorship analysis of the 50 most productive countries. In a co-authorship analysis, the relatedness of items is determined based on the number of co-authored publications. From this figure, it can be seen that while China is the most productive country, Chinese authors tend to collaborate less with researchers in other countries as shown by the distance between lines. In contrast, American authors tend to collaborate with many countries internationally, while German authors tend to collaborate more with researchers in other European countries. Figure 3 depicts a co-occurrence analysis of the 500 most frequent author keywords used across all publications. In a co-occurrence analysis, the relatedness of items is determined based on the number of publications in which they occur together. From this figure, a number of clusters can be observed representing different TCAIM topics. The yellow, red and dark blue clusters represent a large network of keywords related to laboratory-based studies, while the green cluster represents keywords related to clinical research and review-type studies. The smaller light blue cluster also highlights research conducted on traditional and indigenous medicines. This figure also provides insights into some of the most highly studied diseases/conditions published in TCAIM journals, which include breast and lung cancer, diabetes, anxiety, and low back pain.

Fig. 2
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Co-Authorship Analysis of the 50 Most Productive Countries

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Fig. 3
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Co-Occurrence Analysis of the 500 Most Frequent Author Keywords

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Discussion

The objective of the present bibliometric analysis is to capture the characteristics of the research literature published in TCAIM journals. The search conducted on Scopus yielded over 170,000 publications, representing the largest bibliometric analysis of TCAIM literature to date to the author’s knowledge. Since the 1940s, an upward trend with respect to the volume of publications can be observed, with a steep increase observed between the mid-2000s and mid-2010s. This upward trend has continued with 2020 marking the most productive year globally to date. Unsurprisingly, therefore, the production in this body of literature follows Price’s law of exponential growth, which is characteristic of fields of research which have experienced great and continued advances and interest from the international research community; other bodies of research literature that have experienced exponential growth include the topics of medical informatics [43], glaucoma [44], psychopharmacology [45], and antipsychotic drugs [46]. This growth in the volume of research published over the most recent decades can largely be explained by an increase in funding support by government and nongovernment sectors for TCAIM research [47,48,49,50]. In the present study, it was found that China was the most productive country with respect to TCAIM research at 45,860 publications, followed by the United States at 29,523 and Germany at 10,120. A vast amount of research continues to be conducted on traditional Chinese medicine in China [51,52,53], while the United States and Germany have both historically been the leading countries with respect to the research of various TCAIM therapies [31,32,33,34]. While the vast majority of publications were written in English, which is largely regarded as the international language of academic publication, it is also unsurprising that the second most common language was Chinese, and the third was German, as this corresponds with the national languages of the most productive countries. Of the top 20 institutional affiliations responsible for publishing this TCAIM research, 17 originated from China, with the remaining two from South Korea and one from Taiwan; a number of affiliations based in the United States and Germany existed as well, but below the top 20. Additionally, with respect to the top 20 funding sponsors, the countries with the largest number were China and the United States, with six organizations each.

In interpreting these results, the reader should be aware of a number of caveats. For example, authors who have spent more years working in research, and journals that have been publishing for a longer period of time and/or have a greater proportion of their archive indexed in Scopus, will have more publications, citations, and collaborations. Additionally, older publications will have an increased chance of receiving citations, as evidenced by only 15 of the most 100 cited articles being published since 2020. Additionally, it is worthwhile to note that while only the journal’s impact factor was reported in Table 2, other indices are increasingly being used to rank the impact of journals (and authors), such as the H-index and SJR ranking, and differences may be observed based on the metric used.

Comparative literature

The findings from published bibliometric analyses specific to the TCAIM research literature can be compared to that of the present study. One of the first bibliometric analyses of the TCAIM research literature was published by Barnes et al. in 1999 [31]. Using a number of TCAIM-related keywords, the authors conducted searches on MEDLINE and analysed the literature published from 1966 to 1996. At the time, they reported that the volume of TCAIM publications per year rose between 1972 and 1986, and then remained stable and approximated 1500 per year up until 1996. Although in the present study a growth in the volume of literature is still observed from 1986 to 1996, the mean number of publications per year over this decade was approximately 1400, which aligns closely with the findings of the authors [31]. Fu et al. (2011) analysed 17,002 publications found in 19 complementary and alternative medicine journals over approximately three decades [32]. They found that the most productive countries included the United States, China, India, England and Germany, all of which fell within the top seven most productive countries in the present study. A number of institutions were also identified by both Fu et al. (2011) [32] as well as the present study to be among the most productive internationally, including China Medical University and Kyung Hee University. Danell et al. analysed four decades’ worth of complementary and alternative medicine publication activity from 1966 to 2007 [33], then later repeated their study again to include five decades from 1966 to 2016 [34]. In their more recent study, they analyzed 105,216 publications, which prior to the present study, was the largest bibliometric analysis on this topic. Unlike the present study which sought to characterize publications in TCAIM journals, Danell et al.’s (2020) inclusion criteria included publications that had “Complementary Therapies” as their Medical Subject Heading major topic, in the MEDLINE database [34]. Lastly, Youn et al. (2021) conducted a bibliometric analysis of the integrative medicine research literature based on a search query using two keywords joined by the Boolean operator “OR”: “complementary and integrative medicine” OR “integrative medicine”, retrieving and analysing a total of 4660 publications. Although their study’s focus was on integrative medicine, a number of their findings are shared with the present study; for example, they also identified United States, China, and Germany to be the most productive countries (albeit in this order), and they also found that cancer was one of the most commonly studied diseases/conditions [35].

In line with the findings made by Barnes et al. (1999) [31], Danell et al. (2009) [33], Fu et al. (2011) [32], Danell et al. (2020) [34], and Youn et al. (2021) [35], the present study also found an upward trend with respect to the volume of TCAIM research being published each year over the past decades. With respect to the number of publications captured, although Danell et al.’s (2020) study was published in 2020, their coverage of the TCAIM literature only extended up until 2016 [34]. In the present study, over 37,000 publications were found to be published between 2017 and April 2021, comprising over 20% of the entire body of literature analysed.

Future directions

Beyond the aforementioned comparative literature, it is worth noting that it has been far more common for bibliometric analyses to be conducted on a specific TCAIM-related topic. These have included acupuncture [54,55,56], aromatherapy [57], apitherapy [58], complementary and integrative oncology [59], ethnopharmacology [60], homeopathy [61], medicinal plants [62], qi gong [63], and yoga [64, 65], as just some examples among others. Others have conducted bibliometric analyses specific to methodologies, such as clinical trials [64, 66, 67] or guidelines [55] in TCAIM. Bibliometric analyses of the TCAIM literature with specific sub-topics are more straightforward to conduct, as the keywords and searches applied are likewise also easier to standardize. One of the main challenges in conducting comprehensive bibliometric analyses of the TCAIM literature in its entirety is the fact that it is very difficult to operationalize a dynamic and unrelated group of therapies that have been defined on the basis that they lie outside of the purview of conventional Western medical care [68, 69]. As a result, all of the bibliometric analyses of the TCAIM literature to date have been based on searches of TCAIM-specific journals or TCAIM-specific indexed headings, both of which unquestionably provide an incomplete picture of all the TCAIM literature. Thus, future directions of value include 1) the creation of an operational definition of TCAIM informed by a systematic search strategy, and 2) the development of standardized search strategies for major academic databases based on this operational definition.

Strengths and limitations

This present bibliometric study captured and analysed the characteristics of over 170,000 publications, making it the largest conducted to date with respect to the TCAIM literature, and the most comprehensive with regards to TCAIM journal inclusion. Searches were conducted on Scopus as this academic database has a larger coverage in comparison to other databases such as Web of Science. Despite this, it must be acknowledged that all academic databases contain gaps in their indexing, and this was realized at the point of analysis in the present study. Publication data collected from Scopus was not externally verified against another source, and it is also important to note that the number of publications reflect what was indexed by the database as of the search date, and not necessarily the true number of publications published by the included journals themselves. It should be noted that publications included in this bibliometric analysis were based on the fact that they were published in a journal belonging to the “complementary and alternative medicine” category (code 2707), identified based on the ASJC provided by Scopus; as evidenced by Table 2, certain journals that changed names over their history were either not indexed in Scopus or were not included in the same ASJC category. Furthermore, it is always possible that some literature may not have been captured by not searching other databases, however, this would have introduced considerable complexities with respect to the ability to analyse search results efficiently (i.e. deduplication of such a large volume of publications, bibliometric network visualizations). The use of the software tool VOSviewer to create and visualize bibliometric networks serves as an additional strength to the present study, providing a deeper layer of analysis with respect to the strength and nature of relationships between different items (countries, keywords, authors, journals). Two final limitations include the fact that independent search results were extracted and analysed by a single author, and therefore, were prone to increased error as opposed to had the analysis been conducted in duplicate; additionally, results were not screened as this would have been impractical, and possibly unfeasible without the application of an operational definition of TCAIM. Without doing this, however, it is possible that this analysis also included non-TCAIM literature published in journals categorized as “complementary and alternative medicine” by Scopus.

Conclusions

The present study provides current insight into the characteristics of publications published across TCAIM journals, and represents the largest bibliometric analysis conducted to date with respect to the TCAIM literature. The most productive countries included China, the United States, and Germany; unsurprisingly, a large proportion of common institutional affiliations and funding sponsors associated with this subset of publications also originated from these countries. The volume of publications has increased steadily since the 1940s, and a steep increase was observed between the mid-2000s and mid-2010s, which is largely attributable to increased available funding for TCAIM research globally. This upward trend has continued with 2020 marking the year with the most publications to date. Beyond identifying the large diversity of TCAIMs studied, this study also highlights therapies which may be understudied and warrant further investigation. Given a high prevalence of TCAIM use among patients, increased acceptance of TCAIM among conventional healthcare providers, and growing interest in the research of TCAIM, future work should continue to investigate and track changes in the publication characteristics of the emerging research on this topic. The creation of an operational definition of TCAIM informed by a systematic search strategy, followed by the development of standardized search strategies for major academic databases based on this operational definition, may serve to achieve these goals more comprehensively.