Taehan Tangnyobyong Hakhoe (Korean Diabetes Association, KDA) was founded in 1968 with 30 members. By 2014, it had more than 3,000 society members. Its aims are to promote people's health, to encourage medical progress through active academic exchange between members and to develop research in the fields of diabetes and metabolism. To fulfill those aims, KDA began to publish Tangnyobyong (The Journal of the Korean Diabetes Association), with volume 1, number 1 issue in 1972 continuing up to volume 31, number 6 in 2007. It then continued as the Korean Diabetes Journal from volume 32, number 1 in 2008 to volume 34, number 6 in 2010. In 2009, KDA decided to change the text language from Korean or English to English only beginning with the issues published in 2010. The purpose of the language change was to include Korean Diabetes Journal in PubMed Central (PMC) and PubMed and thereby make the invaluable research results from Korea and other countries accessible via the web to physicians, researchers, patients and their families, and other interested people throughout the world without any access barriers [1,2]. KDA also hoped that the Korean Diabetes Journal would be competitive in the worldwide journal market given the high level of research activities and medical service in Korea. In 2011, the journal underwent another change in title to Diabetes & Metabolism Journal (DMJ) to broaden its scope to these worldwide problems. Because 4 years have passed since the change of language into English only, it is time to thoroughly examine the journal's position in the worldwide journal network based on journal metrics. The results can be used to assess whether the change in the journal's language policy was successful based on journal metrics.

The change in the language of DMJ to English only can be considered successful based on journal metrics. Its citation frequency, according to Web of Science, increased markedly after the change in language. Its impact factor, according to Web of Science, increased from less than 0.01 to 1.907, excluding self-citations. The number of total citations also increased rapidly starting in 2011. There was no marked change in the impact factor or the total citation from KoMCI, indicating that the number of readers of DMJ in Korea had reached its peak level prior to the change in the language policy. The proportion of funded articles from 2010 to 2013, i.e., 43.9% of the original articles, is also remarkable. These articles had been screened by funding agencies prior to submission, and the quality of the article is thus likely to be higher. The proportion of papers from outside Korea began to increase starting in 2000 and was 36.5% in 2013. This increase may have been due to its indexing in PMC, which enabled foreign researchers to find DMJ easily from PMC or PubMed as the journal of submission. The distribution of authors from 64 countries who cited DMJ shows that DMJ contains useful information for researchers throughout the world. The H-index from Web of Science was greater than that from KoreaMed Synapse, showing that, although DMJ has been cited by Korean researchers for a long time, its citation by researchers throughout the world has only recently increased. The frequent citation of review articles is a common phenomenon in most journals.

The 2013 impact factor of 2.054 that was calculated from Web of Science, including self-citations, showed that DMJ is a top journal in comparison to the four other SCIE journals from India and Japan in the category of endocrinology and metabolism. This high ranking is believed to be the effect of the journal's inclusion in PMC and PubMed. The increase in its impact factor after being indexed in PMC is a consistent pattern that has been observed with other medical journals from Korea [10]. To be included in PMC, the production of journal article tag suite extensible markup language (JATS XML) file is mandatory [11]. Because it is not difficult to produce JATS XML file, every medical journal written in English can be added to PMC.

There have been other reports on journal metrics from medical journals in Korea. The dramatic increase in the impact factor of The Korean Journal of Internal Medicine was reported 2 years after the first journal metric analysis. Its impact factor increased from 0.623 in 2010 to 1.274 in 2012, and the journal has a ranking of 70/151 (46.4%) in the category of general medicine of JCR [12,13]. The other example is the International Neurourology Journal, which changed its language policy in 2010 and had an impact factor of 0.857 in 2013, corresponding to 85.7% in the category of nephrology-urology [14]. To obtain immediate results regarding journal metrics, inclusion in Web of Science is necessary because the position of a journal in the journal network can be easily found in this database [15].

For the future progression of DMJ, its style and format should be further considered. Currently, the international standard of scholarly journals is frequently suggested by CrossRef and includes items such as a digital object identifier, CrossMark, and FunRef [16]. DMJ has rapidly applied new technologies, and editors should be alerted when new functions are implemented. Another suggestion is the inclusion of multimedia data, such as voice recording of abstracts [17] and the inclusion of video files. Another policy is leadership to the endocrinology and metabolism category journals in Asia. DMJ can serve as an official journal for neighboring countries in East and South-East Asia, as is Journal of Neurogastroenterology and Motility [18]. The preliminary uploading of the citation XML of accepted articles to PubMed (epub ahead of print) is also mandatory for the rapid propagation of the accepted papers [19]. For rapid and efficient peer review, the cascade peer review system can be considered with cooperation from other diabetes journal editors [20].

In conclusion, DMJ can be considered an international journal according to its international diversity of authors and editors, citations from authors from a variety of countries, sufficiently high proportion of funded articles, relatively high impact factor, and number of total citations.