Visual Mapping of Studies on Vitamin D in Football Players

Vitamin D is important in addition to the general health status of individuals. which induces bone and muscle development, as well as bone and in many mechanisms in the body that affect muscle growth Fat-soluble sterol structure that acts directly or indirectly molecule. Vitamin D also plays an important role in maintaining mineral balance as it ensures the absorption of calcium and phosphorus in the intestine and kidney. Vitamin D Deficiency, It causes the formation of some types of cancer such as colon, diseases such as diabetes, multiple sclerosis and rheumatoid arthritis, and also reduces high blood pressure has been reported to be effective Vitamin D in the body [1,2].

It has been used as a vitamin with hormone properties in recent years due to its ability to be synthesized from cholesterol, stored in fat cells and released into circulation when necessary, its regulatory functions in maintaining mineral balance and its functions in different tissues [3]. Vitamin D is produced endogenously by photochemical reactions in the dermis and epidermis cells of ultraviolet B (UVB) rays. Synthesis in our body from 7-dehydrocholesterol (vitamin D3, cholecalciferol) [4]. Active vitamin D exerts its effect in cells and tissues either genomically through its receptors (VDR) in the nucleus or through voltage-dependent calcium channels in cell membranes [3]. It has been stated that when stimulated through the receptor, the effect of the genomic pathway continues for days or even weeks, and it is still not fully known how many genes it regulates [5].

The best serum value that shows the vitamin D status in the body is the 25-hydroxyvitamin D level. Since this value is a common metabolite for both vitamin D3 and vitamin D2 pathways, the 25-hydroxyvitamin D value provides information about the general condition of the individual. Additionally, since its half-life in the human body is approximately 3 weeks, it provides clearer information about the metabolism of the vitamin [6]. The half-life of 1,25(OH)2D3 is approximately 6 hours and it is approximately 1000 times more potent in the blood than 25(OH)D is lower, 25-hydroxyvitamin D is more ideally measured. It also strengthens its metabolite [7].

Vitamin D deficiency causes clinical, physiological and pathological disorders, and is a defined risk factor especially for osteoporosis and bone fractures [8]. There are studies showing that melanin in the skin of Africans and South Americans inhibits vitamin D production by up to 99%, and that 50-70% of children and adolescents and 90% of Africans and South Americans have vitamin D deficiency [9]. Possible effects include decreasing training quality, prolonging the frequency and duration of injuries and illnesses, and thus decreasing athletic performance [10]. The importance of vitamin D in healing injuries has been reported in studies conducted in water sports and synchronized swimmers [11]. However, since the exact mechanism of action of vitamin deficiency is not clear, it has not yet been fully clarified how it causes disability and structural problems in individuals.

Although the effect of vitamin D on optimal bone health and muscle physiology is known, body inflammation, reduces risks for infectious diseases and some types of cancer. It has been proven by studies conducted to date [12]. However, considering athlete health and performance, the most important function of vitamin A is the muscle and bone development of individuals. will have an impact on development and growth. Research conducted on athletes shows that under normal conditions, bone Vitamin D at a daily level of 20ng/ml is sufficient for health. Although it is important to support immunity in athletes and exercise more like 32-40ng/mg to reduce associated inflammation showed that higher levels may be required [12]. Most studies on vitamin D deficiency have generally focused on muscle physiology. At the same time, the relationship between vitamin D and the cardiovascular system Relationship is also very important for athletes. In a study, elite football, basketball, handball and Vitamin D levels, aortic root, intraventricular septum diameter in 506 athletes including volleyball players Structural heart parameters such as were compared, 25(OH)D In athletes showing insufficiency, insufficient and sufficient levels These structural parameters are smaller than athletes with It has been stated that [13].

Football has became increasingly an important part of daily life in every society throughout the history [14]. Football is defined as a highly coordinated sports discipline in which aerobic and anaerobic efforts are used consecutively and factors such as speed, strength, agility, flexibility, mobility, balance, muscular and cardio-respiratory endurance and coordination affect performance together. Performance in football develops depending on many variables such as technical, tactical, biomechanical, mental and physiological areas [15]. Performance and strength, especially in football, are closely related to height, body weight and flexibility levels [16]. Being durable is as important as being fast in football. The reason is that the football game is played at high tempo for long periods of time. In order for the players to adapt to this situation, efforts are made to improve strength, endurance, speed, coordination and flexibility with scientifically based training, while also optimizing body composition [17].

Research model: This study employed a bibliometric analysis to examine research on vitamin D in football players. Bibliometric analysis is a quantitative method that allows for the examination of the characteristics and development of scientific output [18]. This method statistically presents specific features of scientific publications, such as authorship, author collaboration, cited authors, topics, and publication information, through visual maps and networks [18-21].

Bibliometric analysis procedure: The bibliometric analysis in this study involved two primary procedures. The first procedure assessed the scientific output performance, enabling the evaluation of the impact of the research field and its scientific actors, including countries, universities, and authors [22,23]. The second procedure employed a combination of clustering techniques to analyze the topics, disciplines, and research themes, revealing the cognitive structure and dynamics of the research field [24,25].

The sample for this study consisted of 132 publications on vitamin D in football players, published between 1975 and 2024 and indexed in the Web of Science Core Collection (WoSCC). WoSCC was selected for its inclusion of scientific publications with the most significant impact and its status as a primary criterion in academic decision-making.

Search Criteria and Source Identification: Relevant publications were identified through keyword searches in the WoSCC database. Software and Data Extraction: The data retrieved from WoSCC were prepared for bibliometric analysis using VOSviewer software. Data Analysis and Interpretation: The collected data were analyzed using VOSviewer (version 1.6.19). High-frequency keyword cooccurrence analysis, a form of co-word analysis, was utilized in the second stage to identify leading topics and assess the research status in the field. This analysis method was applied in the second stage of the study, and the findings were interpreted accordingly [26,27].

Examining the distribution of publication types, as illustrated in the table, research articles constitute the works largest share. Out of a total of 132 records, 107 are articles, making up 81.061% of the. Additionally, there are 16 review articles, representing 12.121%, and 4 book chapters and 4 editorial materials, each accounting for 3.030%. Furthermore, there are 3 meeting abstracts, comprising 2.273% of the total. This distribution indicates that a significant portion of the works is research-based (Table 1 & 2).

Table 1:Distribution of publications by type.

Table 2:Distribution of publications by scientific field.

When examining the distribution of publications by field, sports sciences account for the largest share at 46.21%. Research related to nutrition and dietetics comprises 27.27% of the publications. Physiological studies make up 9.8%, orthopedic studies 8.3%, and public health-related research accounts for 6.06%. Publications under general medicine constitute 5.3%. This distribution indicates that a significant portion of the research focuses on sports sciences and nutrition and dietetics (Figure 1).

Figure 1:Distribution of authors’ citation counts and link strengths.

Figure 2:Distribution of authors’ publication counts and citation numbers.

Jukic’s study from 2020 received 128 citations with a total link strength of 22. Shaw’s 2017 study received 120 citations and has a total link strength of 8. Owens’ 2018 study garnered 117 citations and has the highest total link strength in the list, which is 254. Bongiovanni’s 2020 study received 90 citations and a total link strength of 69. Hamilton’s study from 2014 has 85 citations with a total link strength of 146. Waddington’s 2005 study received 79 citations, but its total link strength is recorded as zero. Morton’s 2012 study received 74 citations with a total link strength of 113. Maroon’s 2015 study garnered 60 citations and has a total link strength of 133. Koundourakis’ 2014 study received 57 citations with a total link strength of 231 (Figure 2).

Radziminski, Lukasz has the most documents with 7 and has received 62 citations. Knechtle, Beat has 6 documents with 53 citations. Close, Graeme L. has 5 documents but stands out with the highest citation count of 284. Slowinska-Lisowska, Malgorzata has 5 documents with 87 citations, while Jastrzebska, Joanna has 5 documents with 51 citations. Zagrodna, Aleksandra has 47 citations across 5 documents. Jastrzebski, Zbigniew has 83 citations from 4 documents, and Lombardi, Giovanni has 62 citations from 4 documents. Ksiazek, Anna has 45 citations from 4 documents, while Skalska, Maria has 21 citations from 4 documents. Farooq, Abdulaziz and Hamilton, Bruce both have 3 documents and have each received 149 citations (Figure 3).

Figure 3:Visual mapping of authors’ publication distribution and interconnections.

The colors red, green, blue, and yellow represent authors who are central to studies on the topic. The analysis of author relationships reveals four primary centers and their interconnections. Radziminski Lukasz is at the center of the red network, while Knechtle Beat is a key figure in the common network. Klose Graeme is highlighted in yellow, representing a central node in terms of work and connections. Lombardi Giovanni, marked in green, is a leading author whose work is related to other centers. The graph illustrates that Radziminski Lukasz, indicated in red, forms the core of significant studies in this field.

These studies are also influential in related research; for instance, the works of Knechtle Beat and Skalska Maria are notable among these shared studies. Additionally, Lombardi Giovanni’s work, marked in green, plays a significant role and connects to other relevant studies. The works of Faruk Abdülaziz, shown in blue, and Klose Graeme, indicated in yellow, represent central points of intensity and highlight their shared contributions. Overall, studies marked in red form the foundation of this research and represent the primary central points (Figure 4 & 5).

Figure 4:Density map of the relationship between publication and citation counts by country.

Figure 5:Distribution of publication counts and total citation counts by country.

most documents, with 26 documents receiving a total of 419 citations. England, with 24 documents, has the highest citation count at 631. Poland also has 24 documents with 291 citations. Italy has 19 documents that have received 393 citations. Spain, with 17 documents, has garnered 349 citations. Greece has 178 citations from 8 documents, while Switzerland has 80 citations from 8 documents. Both Canada and Brazil have 6 documents; Canada has received 86 citations, while Brazil has 81 citations. Turkey has 6 documents with 25 citations, whereas Qatar, with 5 documents, has received 295 citations. As shown in the density map, the USA, England, and Poland form the central density of research. The density map illustrates that Poland and Spain have a significant number of studies and related research. Countries shown in green have lower publication and citation densities, indicating fewer publications and citations. The strength of international cooperation score increases from blue to red (blue-green-yellowred) (Figure 5 & 6).

Figure 6:Visual map of keyword density.

The strength of international cooperation score increases from blue to red (blue-green-yellow-red). The analysis are vitamin D, athletes, football, and soccer. These keywords represent the focal points of the research and will guide future studies in this area. Vitamin D appears 28 times, football 20 times, soccer 20 times, and athletes 12 times in the keyword frequency. The intensity of these keywords may be related to the country in which the studies were conducted; for example, the term soccer is more prominent in the United States, making it a central keyword following football. Additionally, most studies focus on the direct relationship between vitamin D and football, highlighting the centrality of these concepts in the research. In the study, the occurrences of key terms are as follows: Vitamin D appears 28 times, while football and soccer each occur 20 times. The term athletes is mentioned 12 times. The term 25(oh)d appears 10 times, and body composition is noted 9 times. Nutrition is mentioned 8 times, supplementation occurs 7 times, and physical activity appears 6 times. Additionally, vitamin D deficiency is also mentioned 6 times.

The analysis of publication types reveals key insights into research on vitamin D in football players. As shown in Table 1, research articles dominate, with 107 out of 132 records (81.061%) being original research. This highlights the central role of primary research in this field. Review articles follow, with 16 articles making up 12.121% of the total. These reviews synthesize existing research and identify trends, underscoring efforts to consolidate current knowledge on vitamin D in football players. The dataset also includes 4 book chapters and 4 editorial materials (3.030% each). Book chapters provide in-depth analysis, while editorials contribute to academic discourse. Additionally, there are 3 meeting abstracts (2.273%) and 2 conference papers (1.515%). Meeting abstracts offer brief summaries of conference research, and conference papers preview emerging trends. Overall, the predominance of research articles emphasizes original research, with reviews, book chapters, and other materials enriching the understanding of vitamin D in football players.

The distribution of publications by field reveals that sports sciences account for the largest share at 46.21%. Research related to nutrition and dietetics comprises 27.27% of the publications. Physiological studies make up 9.8%, orthopedic studies 8.3%, and public health-related research accounts for 6.06%. Publications under general medicine constitute 5.3%. This distribution indicates that sports sciences and nutrition and dietetics are the primary focus areas in research on vitamin D in football players. The substantial proportion of sports sciences highlights the extensive nature of scientific studies in this field and signifies its importance as a research area. The most-cited studies have been conducted within the field of sports Sciences.

The high share of nutrition and dietetics suggests that studies examining the relationship between vitamin D and performance are prominent. The lower proportions of physiological and orthopedic studies may imply that these areas are less explored compared to sports sciences and nutrition. The smaller shares in public health and general medicine suggest that these topics have less focus in research specifically on vitamin D in football players. In conclusion, a significant portion of research on vitamin D in football players is concentrated in sports sciences and nutrition and dietetics, while physiological, orthopedic, public health, and general medicine fields have comparatively less research coverage.

Figure 1 shows that some studies have both high citation counts and high link strengths, while others have high citations but lower link strengths. Owens’ 2018 study has received 117 citations and has the highest link strength (254), indicating a broad impact and strong research connections [28]. Similarly, Koundourakis’ 2014 study also shows high citations (57) and significant link strength (231), reflecting both high impact and robust research connections [29]. Jukic’s 2020 study, with 128 citations, stands out but has a lower link strength of 22, suggesting that while it has received many citations, its influence might be more focused [30]. Maroon’s 2015 study also shows 60 citations and high link strength (133), indicating its significant role and impact within the research community [31]. Additionally, some studies exhibit high citation counts but low link strength, suggesting that these studies might be influential within a specific context but may not have a broad impact. Overall, these differences between citation counts and link strengths reflect the diversity of research interaction and academic significance across studies.

Figure 2 displays the distribution of authors’ publication counts and citation numbers. Radziminski, Lukasz has the highest number of documents (7) with 62 citations. Knechtle, Beat has 6 documents and 53 citations. Notably, Close, Graeme L. stands out with 5 documents but the highest citation count of 284, indicating a significant impact of his research. Slowinska-Lisowska, Malgorzata also has 5 documents with 87 citations, while Jastrzebska, Joanna and Zagrodna, Aleksandra have 5 documents with 51 and 47 citations, respectively. Jastrzebski, Zbigniew has 4 documents with 83 citations, and Lombardi, Giovanni has 4 documents with 62 citations. Ksiazek, Anna has 45 citations from 4 documents, while Skalska, Maria has 21 citations from 4 documents. Farooq, Abdulaziz and Hamilton, Bruce each have 3 documents and 149 citations. These data highlight that some authors have achieved high citation counts despite having fewer publications, while others with more publications have received fewer citations. Particularly, Close, Graeme L.’s high citation count suggests that his research has had a broad impact and contributed significantly to the field. In contrast, authors with more publications but lower citation counts might have a more limited influence.

Figure 3 visually represents the distribution of authors’ publications and their interrelationships in studies related to vitamin D and football players. Authors are color-coded to illustrate their roles within the network: Radziminski Lukasz is highlighted in red as the central figure in significant studies within this field. His works form the core of major research efforts and are crucial in linking various studies. Lombardi Giovanni, marked in green, is a leading author whose work is interconnected with other key centers. The blue-shaded Farouk Abdulaziz and the yellowhighlighted Klose Graeme represent significant nodes within the network, each contributing centrally to the research landscape. This visual mapping shows that Radziminski’s red-highlighted studies are foundational to this research area, with notable connections to other works, including those of Knechtle Beat and Skalska Maria. Lombardi Giovanni’s green-marked contributions play an important role, connecting with other related studies. Overall, the studies highlighted in red form the core of this research and represent the main central points, offering a clear perspective on the research dynamics and the interplay between key authors in the field.

Figure 4 shows that the USA, England, and Poland are central to research on this topic, with the USA leading in publication count (26 documents) and England in citations (631). Poland follows closely with 24 documents and 291 citations. Italy and Spain also contribute significantly but have fewer citations compared to England. The density map emphasizes the prominence of the USA, England, and Poland, indicating high publication and citation volumes in these countries. The close association between Poland and Spain suggests a strong connection in their research activities. Conversely, countries like Turkey, with fewer publications and citations, demonstrate a less prominent research presence. Figure 5 further highlights the strength of international research collaborations. The color gradient from blue (low cooperation) to red (high cooperation) indicates varying levels of research partnerships. Red areas denote strong collaborative networks, while blue areas show weaker connections. The map underscores the significant international research ties among the USA, England, and Poland, reflecting their key roles in global research collaboration and suggesting that these countries are at the forefront of international research efforts.

Figure 6 shows the visual mapping of keyword density, with a gradient from blue to red indicating the strength of international cooperation. The prominence of “vitamin D,” the most frequently mentioned term, underscores its critical role in the research landscape. The frequent appearance of “football” and “soccer” suggests their significant relevance, though the regional dominance of “soccer” in the U.S. compared to “football” elsewhere points to regional variations in terminology and focus.

The term “athletes” being cited multiple times indicates a strong emphasis on their role in the context of vitamin D and sports. The presence of terms like “25(OH)D” and “body composition” also highlights their importance in understanding the relationship between vitamin D and athletic performance. Meanwhile, “nutrition,” “supplementation,” and “physical activity” are mentioned less frequently but still contribute to the broader context of research. These patterns suggest that regional preferences and terminological differences play a role in the distribution of keywords. Future research should consider these factors to provide a more comprehensive understanding of how regional contexts influence the focus and outcomes of studies. The centrality of “vitamin D” in the research underscores its significance and indicates that future studies should continue to explore its impact on athletes and related health outcomes.

The bibliometric reveals a predominant focus on sports sciences and nutrition, with research articles being the most common publication type. High-impact studies and notable contributors underscore the significance of primary research and international collaboration, particularly from leading countries in the field. While the research is well-developed in sports sciences and nutrition, there are opportunities for further exploration in less examined areas like physiological and orthopedic studies. Future research should leverage these insights, taking into account regional variations and collaborative networks, to enhance our understanding of vitamin D’s impact on football players.

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