INTRODUCTION
Hypertension is a significant risk factor for cardiovascular diseases (CVD)1,2 and affects more than two-thirds of the older population in most industrialized nations.3 The global population of hypertension is estimated to be more than 1 billion with a continuous increase and is emerging as a serious worldwide public health issue.3 Lifestyle factors, such as physical activity (PA) and nutrition, are recognized as critical modifiable determinants of hypertension.4,5 Therefore, intensive efforts to promote these strategies are required to lessen the considerable public health burden of hypertension on a global scale.
Accumulating data suggest that physical inactivity and/or inadequate PA are associated with metabolic outcomes that contribute to cardio-metabolic diseases (e.g., type 2 diabetes and CVD) and increased risk of all-cause mortality.6 On the contrary, many studies have shown that regular PA can exert various protective effects on such complications.7 In particular for blood pressure (BP) regulation, not only regular PA can reduce systolic BP by 3 to 5 mmHg and diastolic BP by 2 to 3 mmHg in normotensives,8 but also this effect is even more pronounced in hypertensive subjects: a recent meta-analysis indicated a mean reduction of 7 mmHg systolic BP and 5 mmHg diastolic BP. Therefore, regular PA is broadly recommended by current American and European hypertension guidelines.2,9 To date, the research topic in hypertension and PA has produced numerous publications; however, there have yet to be attempts to identify large volumes and growth patterns of literature affecting the development of the research field.
Bibliometric analysis is a technique used to identify research trends, including the emphasis and contributions made to scholarship by a particular field, country, author, or journal.10 Bibliometric findings can be a crucially significant information source for decision-makers and funding agencies of objective information about the quality and quantity of scientific efforts since these provide measurements of activity, impact, and linkage.11 In addition, analysis of the keywords used by authors or the content of published papers could reveal present and potential future trends in a research area. Although bibliometric analysis is becoming more widespread in various research fields,12-14 no bibliometric investigation has looked at the relationship between the keywords, ‘ hypertension’ and ‘ PA’, in the literature. This study aimed to conduct the bibliometric analysis of literature including two keywords, ‘ PA’ and ‘ hypertension’, expecting our findings to demonstrate the relevance of prior research and current trends while pointing the way for future study. The results from this study would have implications for researchers, healthcare professionals, and policymakers working to treat hypertension with PA interventions. By identifying the most prominent research trends and gaps using bibliometric analysis, this study can guide future research in this area and thus, raise awareness of the importance of PA as a key intervention for treating hypertension.
METHODS
1. Search strategy
Articles containing two keywords, ‘ hypertension’ (including high BP, elevated BP, hypertensive, hypertonicity, arteriopressor) and ‘ PA’ (including exercise, exercise training, resistance training, aerobic training, en-durance training, physical fitness) were searched in the SCOPUS, Web of Science, and PubMed from January 2000 to June 2023. The search was performed on July 19, 2023.
The data extraction initially selected 3,059 papers from SCOPUS, 2,606 from Web of Science, and 1,454 from PubMed. After merging these papers and removing duplicates, 2,568 papers constitute the primary body of literature. Table 1 shows the publication type for the primary body of literature: the majority were original research articles (n=2,042; 83.3%), followed by review articles (n=302; 12.3%) and editorial (n=44; 1.8%). After excluding not-original articles (reviews, editorials, etc.) and not-re-lated articles (animal studies, n=123), a total of 2,042 original research articles were used for the bibliometric analysis (Fig. 1).
2. Bibliometric visualization and mapping
The keywords extracted from the final publications (n=2,042) were independently reviewed by two researchers (S.P. and S.K.), where stan-dardized similar words were examined to unify terms among evaluators. Our primary goals for the bibliometric analysis were as followings: 1) to see the trend of publication year-wise, 2) to reveal the worldwide active authors in this research area and their collaboration, 3) to find other co-occurring keywords which have been studied together with ‘ hypertension’ and ‘ PA’. The co-authorship analysis, international collaboration among countries, and co-occurrence of keywords through the network visualization maps were executed using VOSviewer (version 1.6.19).10 The color and size of the circle, font size, and thickness of connecting lines are used to present specific parameters. For instance, units (such as countries, authors, institutions, or journals) with similar colors belong to one group. The size of the circle or font is indicative of the higher fre-quency of occurrence, greater productivity, or higher number of citations. The thickness of connecting lines (relative link strength) indicates 10
RESULTS
1. Analysis of the growth trend in publication numbers
As shown in Fig. 2, the number of publications including the two keywords has increased from 2000 to 2023, although with a small fluctuation. From 2000 to 2012, the number of publications slowly increased, showing less than 100 publications every year. However, since 2013, the number of publications per year has rapidly increased with more than 100 publications yearly. These results indicate that the relationship between hypertension and PA has received growing attention recently and is a still-ongoing active research topic.
2. Analysis of countries/regions
Authors from a total of 107 countries have published papers including the two keywords. Table 2 shows the number of publications from the top 10 countries and the total number of accumulated citations. Notably, the top 10 countries have published over 99% (n=2,554) of all publications on the research topic. The United States was ranked first (787; 30.8%), followed by Brazil (391; 15.3%) and Germany (217; 8.5%). Of the top 10 countries, four were in Europe, two were in North America, two were in Asia, and one was in Latin America and Western Pacific, respectively.
Table 2.
The top 10 prolific countries ranked by the number of publications
Articles containing the two keywords were published in 276 different academic journals. The top 10 journals accounted for 19.7% of the total publications (Table 3). The top 5 journals in ranks were: Hypertension; American Journal of Hypertension; International Journal of Cardiology; Circulation; and Arquivos Brasileiros de Cardiologia. Circulation had the highest number of citations per paper, followed by Hypertension, and Chest.
Table 3.
The top 10 journals ranked by the number of publications
3. Analysis of authors and co-cited authors
In total, 10,248 authors published 2,042 included papers. Most of the papers (1,875; 91.8%) were multi-authored (≥3 authors), while 116 (5.7%) were two-authored and 51 (2.5%) were single-authored. Accordingly, 97.5% of publications were team-based and throughout the study period, the level of collaboration was close to 100%.
The top 10 most productive authors on the research topic are shown in Table 4. Six were from China, four were from Germany. The researcher, Naeije R, was the most prolific author (n=29) and also had the highest number of citations (n=1,883). Co-cited author analysis demonstrates 10 collaboration clusters of authors (Fig. 3). The two largest clusters are the blue and red clusters, representing Belgium and Chinese research teams, respectively. Both teams have relatively complete cooperation networks.
Fig. 3.
Fig. 3.Visualization map of co-authorship network for hypertension and physical activity research.
Table 4.
The top 10 authors ranked by the number of publications
4. Top cited papers
The top 10 cited papers including the two keywords are listed in Table 5. The article with the highest number of citations (n=1,141) is “ Survival in patients with idiopathic, familial, and anorexigen-associated pulmonary arterial hypertension in the modern management era” published in Circulation in 2010, 15 followed by eight other articles having more than 500 citations.
Table 5.
Top 10 articles ranked by the number of citations
5. Research trends and frequent keyword
The 20 common keywords co-occurred with the two keywords, ‘ hypertension’ and ‘ PA’, were listed in Table 6. The keyword, ‘ BP’, most frequently appeared with the two keywords, followed by keywords related to non-communicable diseases, such as ‘ CVD’, ‘ obesity’, and ‘ diabetes’. Lifestyle and/or risk factors, for example, ‘ diet’, ‘ aging’, ‘ smoking’, and ‘ body mass index’, were also noticed. Fig. 4 reveals the network visualization map for those co-occurred keywords (≥10 times). The map included three clusters of 74 keywords with 27 minimum link strengths and 1,128 maximum link strengths. Each link has a link strength that the number of documents in which two keywords appear together. The group of keywords co-occurred in a way that the sum of the link strengths was 2,248. Keywords with the same color indicate the tendency to have close relations and usually co-occur together. For the cluster with blue, keywords, such as ‘ obesity’, ‘ diet’, ‘ alcohol’, and ‘ sedentary behavior’, commonly appear in the literature with the two keywords, indicating that the lifestyle factors are important research questions related to hypertension and PA. The cluster with red comprises keywords related to diseases and health status such as ‘ CVD’, ‘ diagnosis’, ‘ rehabilitation’, and ‘ hypertrophy’. This suggests that the relationship between BP and PA is one of the key mod-ulators influencing the individual's health and lifespan. The green cluster consists of keywords associated with organ (herein vessel) function and structure, i.e., ‘ endothelium’, ‘ inflammation’, ‘ arterial stiffness’, and ‘ oxidative stress’, which are popularly studied as the mechanisms in which PA exerts lowering effects on high BP.
Table 6.
Top 20 keywords ranked by the number of co-occurrences
DISCUSSION
In the present study, we applied bibliometric analysis to review the literature published between January 2000 and June 2023 on hypertension and PA research and presented findings of bibliometric maps and tables. The results found that the number of publications increased slowly during the first decade (from 2000 to 2009), but after that, rapidly grew up to date. This trend reflects the growing interest of institutions and researchers in hypertension and PA, highlighting its essential position in human disease, health, and lifespan worldwide.
The United States was the most productive country in the research area, and most of the top 10 prolific countries represented developed economies. We observed a similar pattern for leading institutions and productive authors in the research topic. For example, the United States, Brazil, Germany, China, and Italy contributed the most to the published literature. This could be considerably associated with several factors, for example, existing national recommendations and guidelines for PA, medical infrastructure, funding resources, and the presence of leading organizations that focus on promoting PA. Of note, developing countries have made subtle contributions to this research area, and researchers from these countries are less likely to publish in indexed journals. This might be related to factors such as insufficient funding, inaccessibility of objective hypertension and PA measurement, the absence of research resources, and a lack of awareness of the importance.16 The limited research may also be relevant to a lack of national-level PA policies for treating hypertension in developing countries.17 However, considering the rising burden of CVD in such low- and middle-income countries,18 efforts should be made, especially for those countries, to encourage research on PA as an approach for treating or preventing hypertension. This could be initiated in several ways, such as fostering collaborations with prominent researchers or institutions and building a pool of professionals capable of instructing PA for hypertensive patients.
The author keyword visualization map demonstrates that hypertension and PA research have primarily focused on non-communicable diseases, while communicable diseases were rarely addressed. This was in line with previous studies in that both hypertension and PA have been widely studied, considering for chronic disease complications such as CVD, type 2 diabetes, and cancers.6 Given that either hypertension or insufficient PA is widely known as a solely independent risk factor for metabolic diseases,1,6 the potential role of PA in treating hypertension would provide health benefits in that PA can not only reduce the preva-lence of hypertension, but also decrease the complications of chronic diseases like diabetes. These results support the need for future studies to determine the association of combined hypertension and PA with communicable diseases, such as flu, hepatitis, and seasonal virus diseases.
The results from this study can provide the historical basis and justification for further hypertension and PA research and are therefore cru-cial to future scholars.13 It is now well documented that PA is an efficient non-pharmacological way to treat/prevent hypertension.7 Thus, publications on the effects of PA on hypertension continue to be studied further and are therefore expected to be frequently cited. The future challenges could be the study of finding individualized and economically viable PA interventions for hypertension treatment/prevention.19
The present study has several limitations. Publications in non-English journals that are not indexed may have been unnoticed, and these have not always been easily included.12-15 The search query we used might also have missed some relevant papers. Nonetheless, we have tried to limit these concerns by manually reviewing the papers and by including those irrespective of the language publication. Finally, as a natural limitation of databases, the identities of authors and institutions may have needed to 10
CONCLUSION
This study represents the first attempt to conduct a bibliometric analysis of literature in the field of hypertension and PA research. The results indicate that publication output has significantly increased across various disciplines over the last two decades. In addition, citations have increased during the period, suggesting that researchers, clinicians, and policymakers are becoming more interested in this topic. Institutions, authors, and journals from developed countries have primarily contributed to this research field with significant contributions from North America and Europe. Contributions have also come from some countries in East Asia (e.g., Japan and China) and Latina America (e.g., Brazil). Despite of rising burden of CVD in such low- and middle-income countries, developing countries have had a negligible contribution to the literature. Thus, research collaboration should be strengthened to in-clude researchers from developing countries encouraging PA levels in hypertensive patients and even healthy individuals. Our findings also demonstrate that chronic disease complications, such as ‘ diabetes’, ‘ obesity’, and ‘ CVD’ were found to be the most popular research agenda associated with hypertension and PA.
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