Global research on vitamin D and coronavirus disease 2019: A bibliometric and visualized study

Vitamin D play a substantial role in immune function, but little is known about its prevention in coronavirus disease 2019 (COVID-19). A detail bibliometric analysis of the published scientific literature indexed in Web of Science on vitamin D as a therapeutic option for the COVID-19 patients' treatment is lacking. Thus, the current study was conducted to determine the key bibliometric indices and plot the global research on vitamin D and COVID-19.

The Web of Science Core Collection database was utilized to retrieve publications on vitamin D and COVID-19. A Boolean search strategy was applied and the obtained data were exported to Microsoft Excel to generate relevant graphs. Furthermore, VOSviewer software version 1.6.17 for Windows was used to generate co-authorship countries, bibliographic coupling sources and co-occurrence keyword network visualization mapping. In addition, RStudio and Bibliometric online tool were used to generate WordCloud and thematic map, and intercountries relation map, respectively.

A total of 818 publications on vitamin D and COVID-19 were included in the final analysis. These publications were cited 10,713 times, with an H-index of 50. The number of publications and citations score from 2020 to November 2021 increased from 317 (2423 citations) to 501 (8290 citations). Delanghe JR and Speeckaert MM were the most prolific authors with 13 publications each. The most productive journal was Nutrients (n = 63). The most studied research area is nutrition dietetics. The most widely used author keywords were COVID-19 (n = 444), Vitamin D (n = 312), and SARS-CoV-2 (n = 190). The National Institute of Health and US Department of Health and Human Services were the leading funding agencies. Harvard University was the most active institution with 25 publications. The United States of America was the highly contributing and influential country in terms of publications (n = 203) and total link strength (n = 185).

It was concluded that an increasing trend in the number of publications on vitamin D and COVID-19 has been observed. Significantly, the majority of the research has been conducted in developed countries. Most importantly, over the time, the direction of research has been changed and the recent trend topics are vitamin D deficiency, risk and infection, and vitamin D supplementation based on KeyWords Plus. The use of vitamin D supplement is one of the promising therapeutic options for COVID-19 treatment. Therefore, the current study not only highlight the global research trends but also provide standard bibliographic information for future studies.