A bibliometric analysis of epidemiological studies investigating the relationship between community fluoridated water consumption and human cancers

INTRODUCTION

Dental caries can be defined as a multifactorial, biofilm-mediated, sugar-driven, and dynamic disease that is characterized by the localized destruction of the mineralized structures of the tooth.^[1] According to the World Health Organization, dental caries is the most common noncommunicable diseases globally, affecting over 2 billion people.^[2] If dental caries is not treated early, it can progress into serious complications – such as pulpitis, pulpal necrosis, odontogenic abscess, sinusitis, and others –which can significantly reduce the quality of life of the person affected.^[2-4] The economic implication of dental caries is so enormous;^[2] for example, the cost of treatment of dental caries consumes about 5–10% of the health-care budgets of industrialized countries.^[2]

As part of dental public health protection strategy, community water fluoridation has been used to significantly reduce the burden of dental caries across populations.^[5,6] The history of water fluoridation can be traced to Colorado Springs, Colorado, in 1901, when Dr. Frederick McKay – a fresh dental graduate – discovered “mysterious” brown stains in the teeth and decided to investigate the cause.^[7] In his research journey, Dr. McKay met Dr. G.V. Black – a renowned American dentist – in 1909 who agreed to collaborate with him in tracing the root cause of the brown teeth stains among Colorado people.^[8] Together, they discovered that those teeth with “mysterious” brown stains were highly resistant to dental caries.^[8] Thereafter, there arose a growing interest, in the scientific communities, concerning the phenomenon discovered by McKay and Black.^[8] Eventually, in 1931, McKay discovered that those brown dental stains – dental fluorosis – occurred due to high fluoride levels in drinking water.^[8] In the late 1930s, Dr. H. Trendley Dean – a researcher at the National Institute of Health (USA) – and his staffers discovered that a fluoride concentration of 1.0 part per million rarely cause dental fluorosis.^[8] By 1945 – the year when the World War II ended – the first trial of the effectiveness of community water fluoridation programs in dental caries prevention began in Grand Rapids, Michigan.^[8] The Grand Rapids water fluoridation project took 15 years, and from the project, it was proven that the fluoridated water consumption reduced the caries rate in children living in Grand Rapids by 60%.^[8]

Since the Grand Rapids discovery, may cities in the US, as well as several other places in the world, have incorporated community water fluoridation into their dental public health programs.^[8]

In 1999, the Center of Disease Control and Prevention regarded community water fluoridation as one of the 10 greatest achievements in public health in the 20^th century due to the huge successes, it has recorded in the reduction of the global disease burden of dental caries.^[6]

However, there have been a lot of controversies and debates regarding the safety profile of fluoridated water.^[9] For example, there is an ongoing debate in the scientific community about the role of fluoridated water in cancer development in humans; and different epidemiological studies had been conducted to establish or refute this relationship.^[10-22] While some studies reported no relationship between fluoridated water consumption and cancer occurrence, others reported a direct or an inverse relationship between them.^[10-22]

Despite the significant quantity of epidemiological studies that had investigated the relationships between community water fluoridation and human cancers, no known study has the quantity of the existing epidemiological evidence. Therefore, there is a need for a bibliometric analysis of these studies. A bibliometric analysis is a kind of research which seeks to statistically measure the impact of research publications and the researchers or organizations investigating a topic area of interest.^[23-29] Through bibliometric analysis, research hotspots and the trend of productivity on a research topic area can be evaluated.^[30]

MATERIAL AND METHODS

RESULTS

In the SCOPUS and PubMed databases, only 12 epidemiological articles on the topic area of interest (i.e., epidemiological studies investigating the relationship between community fluoridated water intake and cancer occurrence) were written in English, with accessible full text, and published between 2000 and November 23, 2021. These articles were authored by a total of 70 authors [Appendix 1].

Trend analysis

Figure 1 shows the trend analysis of the included epidemiological articles by year. Not all years had an article published on the research topic area. The years with the highest outputs were 2014 (n = 2) and 2019 (n = 2).

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Figure 1:

Trend analysis, by year, of the included articles.

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Funding

Less than half (5/12) of these articles were funded [Figure 2]. [Table 7] shows the information regarding the external funding sources (grants) of these articles. The UK was the country with the highest number of funding organizations on the research topic area. None of these funding organizations are situated in the African, Australian, or South American continent.

Table 7: Sources of funding for the funded articles.

Funding organization	Country	Articles funded*
National Institutes of Health	USA	3
CDI Research Inc.	USA	1
International Agency for Research on Cancer	France	1
European Commission	Belgium	1
Union for International Cancer Control	Switzerland	1
Bone Cancer Research Trust	UK	1
National Institute of Health Research	UK	1
Children with Cancer UK	UK	1
National Science Council	Taiwan	1

*Some articles had more than 1 source of funding

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Figure 2:

Funding status of the analyzed articles.

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DISCUSSION

The findings obtained in this study are noteworthy. The volume of epidemiological studies investigating the relationship between community fluoridated water intake and cancer occurrence, published within the past two decades, is very minute compared to that recorded concerning research on other cancer topics;^[31-33] for example, the annual publication rate in cancer rehabilitation research is currently 136 articles per year.^[33] Overall, this suggests that the level of global research interest on fluoridated water and cancer is low.

However, the country with the highest number of articles, authors, and institutions on the topic area is the USA. Furthermore, based on the number of articles per funding institutions, the USA is the home to the biggest funder of epidemiological studies on this topic area. This finding is consistent with that recorded concerning research in many other research topic areas.^{[25,31,33-37]} The reason why the USA has dominated the research world may be due to the huge pot of funding its government apportion to research and development.^[38]

It is also noteworthy that these studies investigated different cancer sites. However, the most investigated cancer site was the bone. The reason why majority of these studies focused on bone cancer may be because bone cancer is the most debated risk factor associated with fluoridated water consumption.^{[10,11,13-17,22]}

This study has its limitations. First, only those articles written in English with accessible full text were included in this study; this means that those articles written in other languages and those without accessible full texts were excluded from the study. However, all articles written in English were retrieved through our institutional library, except the article by Steiner^[12] which was inaccessible. Second, only those articles published from 2000 upward were analyzed in this study; studies older than 2000 were excluded from the study, and this may be considered as a limitation. Therefore, not all articles published on the topic since the inception of research on the topic area was included in this study.

Notwithstanding this limitation, this study has its strengths. First, to the best of the authors’ knowledge, this study is the first to do a comprehensive bibliometric analysis of articles on this topic area. Second, this study has identified the research hotspots concerning the topic area, which no other known study had identified these spots. Third, unlike most bibliometric analysis which used only one database, this study used the two largest databases of health literatures in the world.^{[23-31,33-37]}

CONCLUSION

The volume of research investigating the relationship between community fluoridated water intake and cancer occurrence is very low, with zero output from several countries. Globally, the USA is the hottest spot for research on this topic area.