Global hotspots and trends on environmental exposure and cardiovascular disease from 1999 to 2022

Abstract

BACKGROUND

The increasing risk of cardiovascular disease (CVD) associated with worsening environmental exposure is a critical health concern garnering global research attention.

AIM

To systematically assess the scope and characteristics of research on the relationship between environmental exposure and CVD.

METHODS

A thorough examination of publications on the relationship between environmental exposure and CVD from 1999 to 2022 was carried out by extensively screening the literature using the Web of Science Core Collection. The language of the selected publications was standardized to English. Afterward, different academic tools such as CiteSpace, VOSviewer, HistCite, Python, Matplotlib, and Bibliometrix were utilized to examine the research trends in this field.

RESULTS

The study’s findings indicated a steady increase in scientific publications among the 1640 analyzed documents, peaking in 2022 with 197 publications. The United States emerged as the leading nation regarding high-quality publications and international collaboration. Harvard University was identified as the most prolific institution. “Environmental research” was the most frequently contributing journal, and Muenzel T was recognized as the top contributor. Current research hotspots are primarily concentrated on themes such as “cardiovascular disease”, “exposure”, “risk”, “mortality”, and “air pollution”.

CONCLUSION

This study highlights increasing research on the link between environmental exposure and CVD, identifying key exposures and diseases while emphasizing the need for further investigation into underlying mechanisms.

Key Words: Bibliometrics; Environmental exposure; Cardiovascular disease; CiteSpace; VOSviewer; Web of Science

Core Tip: Environmental exposure plays a pivotal role in the development of cardiovascular diseases (CVD), which are a leading cause of global morbidity and mortality. Over the past 23 years, research in this field has expanded significantly, reflecting its growing importance. Various environmental exposures, including particulate matter, nitrogen dioxide, and ozone, have been linked to major CVDs such as coronary heart disease, hypertension, and heart failure. However, while existing studies have proposed potential mechanisms, the pathways connecting environmental exposure to CVDs remain insufficiently understood. This study provides a comprehensive analysis of global research trends and identifies key areas for future investigation.

INTRODUCTION

Environmental exposure encompasses a broad spectrum of non-genetic risk factors that individuals encounter through air, water, soil, and other mediums[1]. These exposures include particulate matter (PM) and noxious gases from industrial and vehicular emissions, various organic and inorganic chemicals from agricultural and household sources, heavy metals like lead and mercury prevalent in polluted environments, and electromagnetic and ionizing radiations[2]. Additional exposures arise from biological agents such as allergens and pathogens and noise pollution from urban and industrial activities[3,4]. Collectively, these environmental factors have been linked to an array of adverse health outcomes, including increased incidences of respiratory[5], cardiovascular disease (CVD)[6] and neurotoxicity[7], thereby posing significant public health challenges[1,8].

CVD, including ischemic heart disease, stroke, heart failure, peripheral vascular disease, and other heart and vascular system disorders, is a leading cause of mortality worldwide and a critical factor in the significant decline in quality of life[9,10]. According to data from 2021, CVD is responsible for approximately 18.6 million deaths worldwide annually. This considerable health burden equates to a loss of around 360 million years of potential life and over 170 million years of healthy life[11]. Extensive epidemiological evidence indicates that exposure to environmental exposure increases cardiovascular risk factors such as dyslipidemia, hypertension, atherosclerosis, and diabetes, leading to higher incidence and mortality rates of CVD, including ischemic heart disease, heart failure, and stroke[6,12-14]. These findings highlight the broad impact of environmental exposure on cardiovascular health as a public health challenge, emphasizing the need to strengthen environmental monitoring and health intervention strategies to mitigate its adverse effects on global cardiovascular health[15-17].

The negative consequences of exposure to environmental factors on human health are thoroughly recorded[8,17]. Environmental exposure to PM and industrial emissions has been robustly associated with an increased risk of CVD[6]. PM is a mixture of multi-component aerosols, including metals, elemental carbon, organic compounds, and inorganic nitrates and sulfates[18]. PM_2.5 can induce systemic inflammation and oxidative stress, leading to endothelial dysfunction and atherosclerotic plaque formation[6]. Moreover, exposure to ambient air pollutants like nitrogen dioxide and sulfur dioxide has been linked to alterations in heart rate variability and increased blood pressure, precipitating cardiac events[19,20]. Chronic noise exposure, another environmental risk factor, contributes to hypertension and stress-related hormonal changes, further exacerbating cardiovascular risk[21,22]. These environmental factors significantly contribute to the global burden of cardiovascular morbidity and mortality, underscoring the need for stringent environmental control measures to mitigate their impact on public health[23]. According to the Global Burden of Disease Study in 2019[24], approximately 9 million deaths worldwide were related to air pollution, with 61.9% of these deaths caused by CVD, including ischemic heart disease (31.7%) and stroke (27.7%). Environmental exposure ranks as the fourth leading cause of death among the 73 principal causes worldwide, trailing only high blood pressure, tobacco use, and poor dietary habits, posing a significant public health challenge[11].

However, numerous pressing issues remain unresolved regarding the complex association between environmental exposures and CVD. First, the biological mechanisms by which different types of environmental pollutants affect the cardiovascular system are not yet fully understood[18-20]. Second, research on the dose-response relationships, long-term exposure effects, and individual susceptibility differences to environmental exposures is still insufficient[25]. Furthermore, current studies are predominantly concentrated in developed countries, with relatively less focus on developing countries and regions, limiting a comprehensive understanding of the relationship between environmental exposures and CVD on a global scale[23]. Therefore, in-depth exploration of the mechanisms, regional differences, and prevention strategies linking environmental exposures to CVD has become a research hotspot and trend in this field.

Bibliometrics utilizes citation data from databases to assess published research, systematically studying and visualizing specific scientific fields' knowledge structure and dynamics through qualitative and quantitative analysis of publication cooperation, co-occurrence, and co-citation relationships[26,27]. Bibliometric analysis has been widely applied across multiple disciplines as a powerful tool for tracking scientific theme progress and predicting future research directions[28]. Bibliometric analysis has been utilized extensively in numerous disciplines of medical research, such as cardiology[29], oncology[30], ferroptosis[31], immunology[32], and public health[33], due to its potent prognostic function for the research outlook. The environmental exposure and human health bibliometric analysis has been published[34]. However, specific bibliometric studies in the interdisciplinary research area of environmental exposure and CVD still need to be included. To address this research gap, an extensive bibliometric analysis was performed on the literature pertaining to environmental exposure and CVD published between 1999 and 2022, utilizing the Web of Science Core Collection (WoSCC)[35]. We utilized various data analysis tools like VOSviewer and CiteSpace to examine information on keywords, authors, institutions, countries/regions, and published journals[36-38]. CiteSpace is a Java-based software designed for literature analysis within specific fields. It enables users to investigate the development trends of related disciplines by generating visual maps utilizing collaborative analysis theory and pathfinding network scaling[39,40]. CiteSpace introduces distinctive concepts such as centrality, burst detection, internumber, and heterogeneous networks, which are instrumental in identifying the characteristics of research frontiers, emerging trends, and abrupt temporal changes, thereby enabling a thorough analysis of field development[41]. Additionally, VOSviewer can create a more intuitive visual representation of the cooperative networks among countries and the clustering analysis of keywords[38].

The aim is to gain a more comprehensive understanding of the complex connections between environmental exposure and CVD, explore research hotspots and frontier trends in this field, and provide a scientific basis for future research directions[42]. Additionally, the findings of this study will assist researchers in exploring new scientific questions, supporting the formulation of evidence-based public health strategies, and ultimately helping to reduce the global burden of CVD.

MATERIALS AND METHODS

Data sources and searches

We chose the WoSCC as the database for obtaining literature, which includes the science citation index, social science citation index, conference citation index, arts and humanities citation index, and others. The Web of Science (WoS) is widely recognized by researchers as a high-quality digital literature database and is considered highly suitable for conducting bibliometric analysis (Table 1). Compared with other databases, it has a strong coverage and provides detailed information for bibliometric analysis[35].

Table 1 Main information from bibliometric analysis.

Category and description	Values
Time span	1999-2022
References	75629
Authors (n)
Authors	8924
Authors of single-authored documents	54
Author collaboration
Single-authored documents (n)	59
Coauthors per document (mean)	7.23
International coauthorships (%)	31.5
Document contents (n)
Keywords plus	3941
Author keywords	3152
Documents
Total documents (n)	1640
Age of document (mean)	7.84
Citations per document (mean)	58.12

The search strategy adopted for this study is shown in Figure 1. The search for papers related to environmental exposure and CVD was conducted on September 10, 2023, in the WoSCC database from January 1, 1999, to December 31, 2022, using the following search strategy: Topic = (“environmental exposure” AND “cardiovascular disease”). The document type was refined to articles and reviews only; book chapters, letters, proceedings papers, editorial material, meeting abstracts, and reprints were all excluded. We focused solely on the documents published in English. Furthermore, we conducted a manual review to examine the content of each paper (including the paper title and abstract) to eliminate repeated and irrelevant publications and ensure that the selected documents were about environmental exposure and CVD. This criterion resulted in a total of 1640 records (1528 articles and 182 reviews). The resulting records were saved as plain text files named download_txt. The dataset contained all the bibliographic information, such as author, title, source, abstract, cited references, and keywords., which were essential for the analysis.

Figure 1  A flow chart displays the process of bibliometric analysis.

Statistical analysis

In this study, the main bibliometric approaches used were: (1) Analysis of cooperation networks. With the advancement of science, scientific research cooperation has become a significant way of enhancing the outcomes of scientific research, and scientific collaboration is vital for information exchange, knowledge dissemination, and resource sharing. Specifically, a cooperative relationship is considered to exist between authors or institutions that appear in the same publication; (2) Analysis of co-citation. Co-citation analysis is a bibliometric approach that creates a co-citation network based on the co-occurrence relationship of references, which can be used to demonstrate the structure and clustering relationship of citations. These two studies constitute a co-citation relationship if they are cited simultaneously by a subsequent study, which varies over time. Consequently, it can investigate the development and evolution of this area. Then, the co-citation analysis of authors and journals was created by extending the concept of co-citation analysis from the references to the author and the journal; and (3) Analysis of co-occurrence. Co-occurrence of keywords refers to the simultaneous occurrence of two or more keywords in a publication. Keywords are an essential component of the publication. In addition to being meticulously considered by researchers, the keywords used in the articles are also intrinsically related. Indirectly, keyword analysis can also disclose a variety of crucial research topics and frontiers in the research field.

Our research concentrated primarily on the following areas: (1) Analyzed the number of publications, using the quantitative visualization report provided by WoSCC to display the changes in the number of publications each year and the distribution of the number of publications across countries; (2) Understood the essential authors, institutions, and journals in the field; (3) Unearthed the highly influential literature in this field and conducted analysis; (4) Comprehended the research frontiers and hot spots; and (5) Explored the future development direction of this field.

In this study, the literature data were comprehensively analyzed and visualized using the following tools. HistCite 2.1 was utilized to provide an overview of the field's development history and identify the most influential literature and authors. Specifically, total global citation scores (TGCS) and total local citation scores (TLCS) were generated using this tool. The literature analysis tools within the WOS database were employed to determine the annual publication volume. Additionally, Python 3.7.5 and Matplotlib 3.1.1 packages were utilized to generate dot-broken line graphs. Furthermore, VOSviewer 1.6.19 was employed to analyze the factor scores and profile descriptions, while Microsoft Charticulator facilitated the mapping of country cooperation networks based on the outputs of VOSviewer[38,43]. This analysis involved examining the number of publications per country and identifying influential countries. The Bibliometrix Online Analysis Platform was also utilized to explore the scientific collaborative networks among institutions. Finally, Citespace 6.2.4R was employed to report burst keywords, co-occurrence maps of keywords, authors, references, and the dual-map overlay of journals in this study.

RESULTS

Analysis of annual publications and citation trends

After a comprehensive search identified 1640 English-language scholarly articles related to “environmental exposure” and “cardiovascular disease”. Cumulative data indicate that these publications have been cited 12991 times, with an average of 58.12 citations per item (average citations per item) (ACI). As depicted in Figure 2, Figure 2A clearly illustrates the annual number of publications and their proportion of the total publications. The data demonstrate a yearly increase in literature on CVD related environmental factors. Figure 2B displays a markedly ascending curve, showing the trend of cumulative literature production. This trend not only reveals a sustained increase in the volume of literature but also symbolizes the rising importance of this research area within the scientific community. Panel C presents the annual TGCS and TLCS. TGCS, a key bibliometric indicator of global academic influence, reflects the citation frequency of articles in the WoS database. Concurrently, TLCS, as a local citation assessment tool, indicates the frequency of citations within a specific research field. Until 2018, despite some fluctuations, the overall upward trend in TGCS reveals a growing global recognition and impact of the research outputs.

Figure 2 Publication outputs and citations about environmental exposure and cardiovascular disease. A: Annual number and percentage of publications; B: Annual cumulative production trends; C: Annual total global citation score and total local citation score of publications; D: Stack bar plot of top 10 countries in publications. TGCS: Total global citation score; TLCS: Total local citation score.

Similarly, TLCS more distinctly mirrors the academic influence of the research on a regional scale. However, since 2018, both TGCS and TLCS have shown a noticeable downward trend. A decrease in recent citations does not necessarily imply that newer publications are cited less frequently than earlier ones. This downward trend might partly be due to a shorter accumulation time required for new publications to garner citations. Although there has been a general decrease in total citation numbers in recent years, the ACI has risen. This suggests that as new studies are continually published, the influence of previously published articles may gradually diminish, even though these new studies require sufficient time to accumulate citations. Considering the volume of publications and citation data, it is evident that environmental exposure issues related to CVD have become an increasingly prominent research topic in the scientific community. It is anticipated that this field will continue to progress and unveil more profound research findings.

Contribution of active countries/regions

From 1999 to 2022, research papers on environmental exposure and CVD were published in 41 countries and regions. Figure 2D displays the annual publication numbers of the top 10 producing countries/regions, indicating rapid growth in publications concerning environmental exposure and CVD. The United States leads this field with 555 papers, accounting for over 33.84% of all included papers and amassing 37601 citations, marking it the pioneer country in researching environmental exposure and CVD. China started its research in this field later but has shown rapid development, contributing 265 papers. The rapid increase in Chinese publications, especially in the last decade, mirrors the country’s growing focus on environmental health challenges associated with its rapid industrialization and urbanization. China’s research often emphasizes large-scale epidemiological studies and the health impacts of air pollution, providing valuable insights into population-level effects and interventions. Meanwhile, despite having fewer publications (n = 87), Germany ranks second in total citations with 9852. Other European countries such as Germany and Spain also hold significant positions in this field (Table 2).

Table 2 Top 10 coauthorships by country using Biblioshiny.

Country rank	Country	Number of documents	Total citations (n)
1	United States	555	37601
2	China	257	8169
3	Italy	87	3542
4	United Kingdom	79	4877
5	Germany	70	9852
6	Canada	55	4951
7	Brazil	49	1127
8	Iran	45	2078
9	Korea	38	1257
10	Spain	34	1303

Figure 3 illustrates the geographical distribution of research on environmental exposure and CVD, highlighting extensive collaboration among countries. Research primarily originates from North America, Europe, and Asian countries. A visualization of the international cooperation network shows close collaborations, with the United States consistently partnering with nearly all other countries.

Figure 3  Geographical distribution in environmental exposure and cardiovascular disease.

Furthermore, the analysis indicates that research involving multiple regions often addresses diverse populations, considering varying genetic backgrounds, lifestyles, and environmental exposures. This diversity enriches the understanding of how environmental factors contribute to CVD across different demographic groups. Studies focusing on vulnerable populations, such as the elderly or those with pre-existing health conditions, are particularly noteworthy, as they provide insights into risk stratification and targeted interventions.

In addition to the quantity of publications, the impact of research from different countries is evident in citation metrics and high-impact journal publications. For instance, despite fewer publications, countries like Australia and the Netherlands have high citation averages, indicating that their research outputs are highly regarded and influential in shaping the field.

Overall, the collaborative landscape and contributions from various countries highlight a growing global recognition of the importance of environmental exposures in cardiovascular health. The increasing trend in publications and international collaborations underscores the urgency and collective commitment to address these challenges through research and policy interventions.

Contribution of productive institutions

Table 3 shows the top 10 institutions with the highest output in studying CVD and environmental exposure factors. Harvard University leads with 66 related publications, achieving a TLCS of 366 and an impressive TGCS of 6967. The University of Michigan and Columbia University are closely followed, with publication counts of 55 and 41, respectively, and TGCS of 4062 and 4550, respectively. Research institutions from various countries, such as the United States Environmental Protection Agency, Johannes Gutenberg University Mainz in Germany, and the Karolinska Institute in Sweden, also demonstrate prominent academic output.

Table 3 Top 10 institutions in environmental exposure in cardiovascular disease.

Affiliation	Articles	Total local citation score	Total global citation score
Harvard University	66	366	6967
University Michigan	55	315	4062
Columbia University	41	124	4550
University Washington	41	185	5523
Johns Hopkins University	34	155	4714
University N Carolina	34	35	989
United States Environmental Protection Agency	34	59	3412
Johannes Gutenberg University Mainz	28	187	1404
New York University	27	106	3098
Karolinska Inst	26	104	3204

The VOSviewer institution collaboration network map (Figure 4) reveals a complex web of cooperative relationships among these institutions, with Harvard University and the University of Michigan occupying central positions in the network. They have established extensive collaborative networks with numerous research institutions globally. This dense academic cooperation has facilitated the exchange and integration of research findings in CVD and environmental exposures, accelerating the innovation and development of scholarly knowledge in this area.

Figure 4  Network map of institutional cooperation by VOSviewer.

Analysis of influential journals and co-cited journals

Table 4 lists the top 15 most productive journals, with “Environmental Health Perspectives” ranking first based on citations and “Environmental Research” having the highest total publications. A network visualization map of cited and co-cited journals was created using CiteSpace, depicting the thematic distribution of scientific journals. As shown in Figure 5, the color bar on the left of the map represents the disciplines of citing journals, while the color bar on the right represents the disciplines of cited journals. Different colored lines indicate citation paths between fields, with the width and color intensity reflecting the strength of citations and the density of cross-disciplinary connections. From the perspective of research on CVD and environmental exposure, three citation paths flow from the “citing journals” section to the “cited journals” section, representing the flow and cross-disciplinary nature of the research. Annotations at the start and end of these paths involve the research fields of the relevant journals. The dual-map reveals knowledge transfer paths from clinical medicine, biology, and immunology to environmental science and ecology.

Figure 5 Dual-map overlay of journals produced by CiteSpace. The color bar on the left side of the figure represents the field of the citing journals, the color bar on the right side speaks for the domain of the cited journals, and the connecting line between them represents the citation relationship.

Table 4 Top 15 journals on environmental exposure and cardiovascular disease, n (%).

Journals	Total publications (n = 1657)	Total citations	CiteScore 2022	Ranking based on citation	Citation Per document	Most cited article	Times cited	Publisher
Environmental Research	76 (4.59)	2615	1.78	3	34.41	Road traffic noise effects on cardiovascular, respiratory, and metabolic health: An integrative model of biological mechanisms	182	Elsevier
Environmental Health Perspectives	74 (4.47)	8516	2.29	1	115.08	The Broad Scope of Health Effects from Chronic Arsenic Exposure: Update on a Worldwide Public Health Problem	820	Res Triangle PK
International Journal of Environmental Research and Public Health	56 (3.38)	1811	4.61	6	32.34	World Health Organization Environmental Noise Guidelines for the European Region: A systematic review on environmental noise and cardiovascular and metabolic effects: A summary	301	MDPI
Science of the Total Environment	50 (3.02)	2610	10.75	4	52.20	Is low-level environmental mercury exposure of concern to human health	294	Elsevier
Environmental Science and Pollution Research	44 (2.66)	672	3.28	15	15.27	Exposure to PM10, NO2, and O3 and impacts on human health	155	Springer
Environment International	39 (2.35)	1355	22.00	8	34.74	Long-term residential exposure to PM2.5, PM10, black carbon, NO2, and ozone and mortality in a Danish cohort	138	Elsevier
Environmental Pollution	37 (2.23)	1215	14.90	9	32.84	Exposure to PM10, NO2, and O3 and impacts on human health	155	Springer
Toxicology and Applied Pharmacology	32 (1.93)	2069	7.20	5	64.66	Pesticides and human chronic diseases: Evidences, mechanisms, and perspectives	687	Elsevier
Plos One	30 (1.81)	712	6.00	12	23.73	Built environment, selected risk factors and major cardiovascular disease outcomes: A systematic review	152	Public Library of Science
Environmental Health	25 (1.51)	936	9.40	10	37.44	Knowns and unknowns on burden of disease due to chemicals: A systematic review	212	BioMed Central
Journal of the American Heart Association	22 (1.33)	705	8.60	13	32.05	Cardiovascular effects of long-term exposure to air pollution: A population-based study with 900845 person-years of follow-up	115	Wiley
Circulation	21 (1.27)	5046	42.10	2	240.29	Air pollution and cardiovascular disease	1661	Lippincott Williams and Wilkins
Chemosphere	20 (1.21)	693	13.30	14	34.65	Children with health impairments by heavy metals in an e-waste recycling area	150	Elsevier
American Journal of Epidemiology	19 (1.15)	1674	7.00	7	88.11	Health effects of dioxin exposure: A 20-year mortality study	158	Oxford University Press
Bmc Public Health	18 (1.09)	757	6.10	11	42.06	The association between green space and cause-specific mortality in urban New Zealand: An ecological analysis of green space utility	310	BioMed Central

PM: Particulate matter.

Analysis of references and co-cited references

Figure 6, generated by CiteSpace, presents a cluster map showcasing the citation analysis results of literature related to CVD and environmental exposure. The 16 color-coded blocks represent 10 thematic clusters, each corresponding to different research directions. These clusters include (1) Air pollution; (2) Environment epidemiology; (3) Environment noise; (4) Hospital admission; (5) Secondhand smoke; (6) DNA methylation; (7) Cardiometabolic disease; (8) Epidemiologic studies; (9) Community noise; (10) Epidemiologic finding; (11) Persistent organic pollutant; (12) Thoracic toxicology perspective; (13) Heavy metal; (14) Chronic arsenic exposure; (15) Plasma; and (16) Carotid-femoral pulse wave velocity. This diversity and breadth illustrate the extensive range of research within this field. By analyzing the co-occurrence relationships within the clusters, it is evident which themes hold central positions in the study of CVD and environmental exposure and the degree of interconnection among different research topics. For instance, the “air pollution” cluster includes citations related to PM and ultrafine particles. In contrast, the “DNA methylation” cluster reflects studies on the molecular mechanisms by which environmental factors affect cardiovascular pathology. Based on these results, works by Miller KA (2007), Cohen AJ (2017), and Van Kempen E (2018) are considered seminal articles in this field.

Figure 6 Cluster diagrams of references. It shows 16 color blocks representing 10 clusters, each composed of articles on the same topic.

Contribution of authors

Total 8924 authors have published 1640 documents on CVD and environmental exposures. Out of these authors, 54 have contributed single-authored documents. Figure 7 is a co-occurrence cluster map that shows the academic community structure within this field. The different colored nodes represent various research authors, and the size of each node reflects the author's output or influence in this field. The lines or links between the nodes indicate co-authorship or academic connections between different authors, with the thickness of the lines representing the closeness of collaboration. The map highlights critical nodes such as Munzel T, Rajagopalan S, and Brook RD, who occupy central positions in the collaboration network within this field. These authors showcase a pattern of close cooperation in studying the effects of environmental exposure on the cardiovascular system.

Figure 7  Author co-occurrence cluster map by CiteSpace.

Analysis of keyword co-occurrence

In Figure 8, the x-axis represents centrality, indicating the importance of a theme, while the y-axis represents density, reflecting the degree of development within the topic research. The upper right quadrant (dynamic themes) features themes with high centrality and density, signifying that they are mature and significant within the research field. Within this dynamic theme, key research areas include “DNA methylation”, “prenatal exposure”, “bisphenol-A”, “oxidative stress”, and “gene expression”. Due to their central position and density, these themes are considered pivotal for supporting knowledge development and enhancement. The upper left quadrant (niche themes) represents internally well-developed themes. This cluster includes topics like “acute respiratory infections”, “biomass combustion”, “ionizing radiation”, “atomic bomb survivors”, “DNA”, “current knowledge defects”, and “cardiovascular malformations”, identifying niche or emerging themes within specific research areas that may hold significance within particular research communities but are not as prominent across the broader field. The lower right quadrant (basic themes) includes foundational and continuously relevant topics in the research field, such as “long-term exposure”, “particulate matter”, “particulate air pollution”, “drinking water”, “national health”, “insulin resistance”, “cardiovascular disease”, and “exposure risk”. Clusters from the lower left quadrant (emerging or declining themes) are marked as less central and less dense; that is, they are less advanced, gradually emerging, and significantly peripheral, with “cancer risk”, “West Bengal”, “skin lesions”, and “blackfoot disease” as main topics. They cover general themes spanning different research areas within the field. This thematic map provides a comprehensive perspective on the research in CVD and environmental exposure, displaying the study’s significant trends and developmental directions.

Figure 8  Thematic mapping of keywords (1999-2022).

A distribution chart of 30 high-frequency keywords was created to understand the evolution of keywords over time, as shown in Figure 9. The vertical axis lists terms based on the keywords provided by authors, while the horizontal axis spans the years from 1990 to 2022. This heatmap encodes the frequency of keywords in medical research by color, ranging from black to yellow, where yellow indicates the highest frequency (value approaching 1) and black represents the lowest frequency (value approaching 0). Key terms in the field of CVD, such as “coronary heart disease”, “myocardial infarction”, and “atherosclerosis”, along with the timeline on the horizontal axis, reveal how academic interest in these topics has shifted over time. For environmental pollution-related keywords like “environmental tobacco smoke”, “PM_2.5”, and “air pollution”, the areas of high-frequency co-occurrence indicate that the link between environmental factors and CVD has been extensively studied at specific times. Over time, the clustering and color changes of these keywords highlight shifts in research focus, such as the rising trends in “oxidative stress” and “inflammation”. This likely reflects an increasing recognition of these pathological processes' roles in the development of CVD.

Figure 9  Thermodynamic map of keyword frequency and national publications.

Figure 10 illustrates the interconnections between critical reference (CR) articles, principal authors, and frequently occurring keywords in the study of CVD and environmental exposure factors. The left field lists CR articles often cited, and the middle field displays authors who have made significant contributions to the research area. The right field presents high-frequency research keywords within the field. Items in each column are interconnected by lines, where the width and number of lines indicate the strength of the connections and the frequency of collaboration between different references, authors, and keywords. The research primarily focuses on keywords such as “air pollution”, “cardiovascular disease”, and “particulate matter”, highlighting central themes and collaborative networks within the field.

Figure 10  Three-field plot among reference, authors, and keywords. Left field: Reference; Middle field: Authors; Right field: Keywords; Number of items in each column: 20. AU: Authors; CR: Reference; DE: Keywords.

DISCUSSION

Recent research increasingly illuminates the link between environmental exposure and CVD, emphasizing the harmful impacts of various environmental pollutants on heart health. Comprehensive studies have established a significant relationship between air pollution and heightened risks of major cardiovascular events, such as stroke, heart failure, myocardial infarction, and hypertension. Data reveals that exposure to pollutants like PM_2.5, PM₁₀, SO₂, NO₂, CO, and O₃ is strongly associated with increased rates of stroke hospitalizations, deaths, and myocardial infarctions[10,38-40]. Additionally, both acute and chronic exposure to air pollution adversely influences cardiovascular outcomes, intensifying hypertension and raising systolic and diastolic blood pressures while lowering pulse pressure[41-44]. Furthermore, air pollution drives cardiovascular morbidity through mechanisms of oxidative stress, inflammatory responses, and endothelial dysfunction, strongly correlating with increased risks of cardiac metabolic diseases[45].

Toxic metal contaminants have been identified as significant risk factors for CVDs. Studies have demonstrated that exposure to arsenic and lead significantly increases the risk of coronary heart disease (CHD) and stroke. Specifically, the relative risk (RR) of CHD due to arsenic exposure is 1.23 (95%CI: 1.04-1.45), and the RR of stroke is 1.15 (95%CI: 0.92-1.43). For lead exposure, the RR of CHD is 1.85 (95%CI: 1.27-2.69), and the RR of stroke is 1.63 (95%CI: 1.14-2.34). Additionally, exposure to cadmium and copper is also associated with an increased risk of CVDs. The RR of CHD due to cadmium exposure is 1.29 (95%CI: 0.98-1.71), and for stroke, it is 1.72 (95%CI: 1.29-2.28). For copper exposure, the RR of CHD is 2.22 (95%CI: 1.31-3.74), and the RR of stroke is 1.29 (95%CI: 0.77-2.17). Furthermore, the relationship between cadmium exposure and heart failure risk has been corroborated by several studies. In a prospective cohort study involving 3348 adults with baseline ultrasound assessments, urinary cadmium was found to be significantly associated with an increased incidence of heart failure, with a hazard ratio of 1.39 (95%CI: 1.01–1.94)[46]. The studies indicate a linear dose-response relationship between exposure to arsenic, lead, and cadmium and the risk of CVDs. In contrast, no significant association has been found between mercury exposure and cardiovascular outcomes[47,48]. Moreover, there are reports linking high S-Cu levels to an increased risk of overall stroke, myocardial infarction, and cardiovascular mortality[49].

There is a growing body of evidence supporting the relationship between noise pollution and CVDs. Cohort studies have demonstrated that the effects of road traffic, railway, and aircraft noise all follow a positive linear trend with the incidence of CVDs. Long-term exposure to traffic noise is positively correlated with an increased risk of cardiovascular events, particularly road traffic noise, which significantly raises the risks of CVDs, stroke, and heart failure[50]. Notably, there are significant gender differences in the impact of noise exposure, with women showing a stronger association between noise exposure and an increased risk of CVDs and mortality[51,52].

Additionally, research on electromagnetic radiation indicates that radiation exposure can initiate or accelerate various pathogenic processes that may increase the incidence of myocardial infarction and stroke[53]. Further studies have revealed that occupational exposure to low-dose ionizing radiation increases the risk of mortality from ischemic heart diseases[54]. These studies indicate that various types of environmental exposure significantly impact the incidence and progression of CVDs. Therefore, further exploration of the mechanisms underlying disease occurrence and the implementation of effective measures to reduce environmental pollution are crucial for the prevention and control of CVDs.

In contrast to systematic reviews or meta-analyses, bibliometric analysis offers distinct advantages in mapping development trends and identifying critical research hotspots within a specific domain. This study represents the first to apply bibliometric techniques to elucidate the knowledge structure and predict emerging research frontiers in environmental exposure and CVD.

This study comprehensively searched the WoSCC science citation index database for publications on environmental exposure and CVD from 1999 to 2022. We identified 1640 relevant publications from 41 countries. Research output has generally increased over this period, with a notable surge in 2020, reflecting heightened interest and understanding of this topic. The average citations per article have varied annually, with TGCS peaking in 2015 and TLCS reaching their highest in 2017-2018, indicating the publication of influential papers during these years. This highlights the need for researchers to prioritize high-impact studies over sheer publication volume. Overall, research in this field is poised to remain a significant area of focus.

To elucidate the spatial distribution of research contributions in this domain, we analyzed and visualized country-specific outputs, presented in Figure 3. Researchers from different regions can leverage the spatial distribution data to optimize their collaborative frameworks strategically, enhancing future research efficiency, expediting information access, and bolstering regional contribution standings. The United States is leading in studying environmental exposure and CVD, with the highest publication volume and extensive collaborations with nearly all research-active nations, followed by China and Italy. Research efforts are predominantly concentrated in North America, Europe, and Asia. Regarding institutional contributions, Harvard University, the University of Michigan, Columbia University, the University of Washington, and Johns Hopkins University emerged as the most active entities headquartered in the United States. The United States has substantially contributed to the volume and impact of publications, underscoring its preeminent role in this research field.

In bibliometric analysis, the evaluation of an author’s research impact is often measured by publication count and citation frequency. According to Figure 7, the study highlights Muenzel T, Schwartz J, Daiber A, Rajagopalan S, and Brook RD, as the leading contributors in terms of publication volume within this field. Notably, Omar H, despite a lower publication count, emerges as the author with the highest citation impact, amassing 6734 citations, underscoring his significant role in pioneering research and collaborative solid efforts. The analysis reveals that researchers focusing on environmental pollution and CVD are predominantly in the United States. United States researchers have made substantial contributions and fostered extensive collaborations within the country. Nevertheless, there is a critical need to bolster international collaborations to enhance the global influence of United States research and further augment scientific output in this field.

By analyzing journal sources (Table 4), researchers can efficiently identify journals best suited for their studies and visualize the most influential journals within the field, facilitating access to cutting-edge research. The examination of the journal and co-cited journal data reveals that “Environmental Research” (n = 76) leads in publication volume, followed by “Environmental Health Perspectives” (n = 74) and the “International Journal of Environmental Research and Public Health” (n = 56). This highlights these journals' substantial interest and contributions to environmental factors and CVD studies. Nonetheless, the CiteScores for these three journals are below 5, indicating a need to elevate the impact of their publications. Conversely, high-impact journals feature fewer articles in this field, suggesting that this area of research may still need to be fully acknowledged and could emerge as a focal point for these prominent journals. “Circulation” is the top-cited journal with 1661 citations, underscoring its pivotal role in the academic landscape. The article “Air pollution and cardiovascular disease: A statement for healthcare professionals from the Expert Panel on Population and Prevention Science of the American Heart Association”[55] is the most cited, reflecting its status as a cornerstone in research linking environmental pollution to cardiovascular health. This study demonstrates that short-term exposure to elevated PM significantly escalates the risk of acute cardiovascular mortality, especially in vulnerable subpopulations. Additionally, hospital admissions for various cardiovascular and pulmonary diseases acutely rise in response to higher ambient PM concentrations. The evidence further indicates that prolonged exposure to elevated PM levels is associated with a reduction in overall life expectancy by several years. Several mechanisms may contribute to this effect, including enhanced coagulation and thrombosis, increased arrhythmogenic potential, acute arterial vasoconstriction, systemic inflammatory responses, and the long-term promotion of atherosclerosis. Systemic inflammation plays a critical role, as exposure to pollutants such as PM_2.5 has been shown to elevate key pro-inflammatory cytokines, including interleukin (IL)-6, IL-8, and tumor necrosis factor-α, which contribute to endothelial injury, increased vascular permeability, and the initiation of pro-atherogenic changes. These inflammatory processes, combined with the suppression of angiogenic growth factors such as vascular endothelial growth factors and platelet-derived growth factor, further exacerbate endothelial dysfunction and promote cardiovascular damage over time. This also indicates that journals contributing significantly to the core literature with high impact are typically of superior quality. Enhancing the balance between the quantity and quality of journal articles is crucial for increasing a journal’s impact. This realization stimulates and incentivizes researchers to broaden and innovate their methodologies. Collectively, literature from highly influential authors in this domain offers a more effective and comprehensive grasp of the foundational theories, advancing the field’s academic depth and breadth.

Keywords are precise distillations of research themes and article content that delineate the literature’s fundamental topics and focal points. Analyzing the co-occurrence of keywords allows researchers to identify the most significant research areas in the field by evaluating the frequency of keyword usage.

The keyword “cardiovascular disease” is the most frequently used, appearing 418 times and ranking first. The primary focus of the keywords is on environmental exposure, including terms such as “air pollution”, “particulate air pollution”, “passive smoking”, and “environmental tobacco smoke”, as well as keywords related to CVD such as “blood pressure”, “coronary-heart-disease” and “myocardial-infarction”. These keywords are prevalent in the literature examining the relationship between environmental exposure and CVD. Our analysis indicates a growing recognition among researchers of the substantial role environmental exposure plays in cardiovascular health, particularly in the context of increasing environmental exposure levels. This underscores the potential for environmental exposure to be a crucial component in strategies for preventing CVD.

Additionally, we observe that keywords related to pathological mechanisms and biomarkers are attracting attention, such as “c-reactive protein”, “lipid-peroxidation”, “superoxide-dismutase”, “serum-lipids”, and “alveolar macrophages”. This suggests a need for more compelling high-impact or highly cited literature in these areas, highlighting the need for further investigation into the specific mechanisms and pathways by which environmental exposure contributes to CVD development. The mechanisms by which environmental noise leads to CVDs are complex and not yet fully elucidated. Continued research is essential to understand the detailed pathways and interactions involved. It's known that noise induces stress responses, including releasing stress hormones like cortisol and adrenaline, which can affect heart rate and blood pressure. However, the precise cellular and molecular mechanisms linking these responses to long-term cardiovascular health outcomes remain unclear[56-58]. Investigations into how noise disrupts endothelial function, alters cardiac autonomic balance, and promotes inflammatory processes are crucial[59]. Additionally, understanding individual susceptibility, including genetic factors, age, existing health conditions, and lifestyle choices, will help to identify populations at higher risk and tailor preventive measures effectively. Advancing research methodologies, including longitudinal cohort studies and controlled laboratory experiments, will enable better isolation of noise effects from other environmental factors like air pollution. This approach will contribute significantly to public health policies to reduce the burden of CVDs associated with environmental noise exposure. This gap represents a promising area for future research, warranting increased attention from the scientific community.

Therefore, future research should focus more on elucidating the specific pathophysiological mechanisms of how environmental exposure impacts CVD and identifying related biomarkers. This focus will not only address existing gaps in current research but also provide a scientific basis for developing new preventive and therapeutic strategies. Such advancements could significantly mitigate the adverse effects of environmental exposure on global cardiovascular health.

In the age of information boom, it is a challenging task for scholars to keep track of the progress of a field. However, as a practical and scientific tool, bibliometric analysis offers a broader perspective of a field's past, present, and future. By analyzing the trends of research in a particular domain over the past few decades, bibliometrics provides valuable information about the trajectory of research. It serves as a helpful resource for researchers to direct future research efforts. Global research trends and hotspots in environmental exposure and CVD are highlighted in this study. Environmental exposure and CVD have received much attention and made breakthroughs during the past 20 years. The current research hotspots mainly include studies on the pathophysiological mechanisms of environmental exposure and CVD. It can aid researchers in swiftly grasping this field's present state and critical areas. In summary, a bibliometric analysis of the rapid advancements in environmental exposure and CVD provides an overview of this period’s history.

This study has several limitations that should be considered. Firstly, the data utilized were exclusively from the WoSCC database, which may result in the omission of pertinent studies indexed in other databases. Secondly, the analysis was restricted to English-language publications, potentially overlooking high-quality articles published in other languages and introducing selection bias. Lastly, recently published high-quality papers may need to be adequately represented in our analysis due to their lower citation rates during data collection.

This bibliometric analysis provides an overview of general research trends and hotspots related to environmental pollutants and CVDs. However, it does not encompass all possible factors due to the vastness of the field. Specifically, research on the effects of formaldehyde and phenol on the cardiovascular system is still in its early stages and was not prominently featured in our study. Future research endeavors should aim to include these compounds to provide a more comprehensive understanding of their potential cardiovascular impacts.

CONCLUSION

This study conducted a bibliometric analysis to investigate the relationship between environmental exposure and CVDs. The analysis results indicate that recent research hotspots in this field are primarily focused on themes such as “air pollution”, “cardiovascular disease”, “particulate matter”, “inflammation”, and “oxidative stress”. The research trends suggest that the impact of environmental exposure on cardiovascular health is receiving increasing attention, particularly regarding the association between air pollution and the incidence and mortality of CVDs. Despite significant progress in this field, more research still needs to be conducted, particularly concerning the specific mechanisms underlying these associations and the effects of less-studied pollutants. In summary, this study utilized bibliometric analysis to emphasize the significant impact of environmental exposure on CVDs, providing a reference for further exploring underlying mechanisms and developing targeted interventions.