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Public perceptions and scientific evidence for perceived harms/risks of community water fluoridation: An examination of online comments pertaining to fluoridation cessation in Calgary in 2011


OBJECTIVES: To examine the perceived harms/risks of fluoridation as expressed in online forums relating to cessation and aftermath in Calgary, specifically, 1) which harms/risks are mentioned, 2) for those harms/risks, what kinds of evidence are cited, 3) to what extent is scientific literature cited, and what is its quality, and 4) for a subset of harms/risks, what is known from the broader scientific literature?

METHODS: Relevant online comments were identified through free-text Internet searches, and those explicitly discussing the harms/risks of water fluoridation were extracted. Types of evidence mentioned were identified, and the scientific papers cited were reviewed. Finally, the broader scientific literature on two of the harms/risks was reviewed and synthesized.

SYNTHESIS: We identified 17 distinct groups of harms/risks, which spanned human body systems, the environment and non-human organisms. Most often, no evidence was cited. When evidence was cited, types included individuals viewed as authorities and personal experiences. Reference to scientific articles was rare, and those papers (n = 9) had significant methodological concerns. Our review of scientific literature on fluoride and 1) thyroid functioning and 2) phytoplankton revealed some negative effects of fluoride at concentrations exceeding maximum recommended levels (>1.5 ppm).

CONCLUSION: The findings have implications for communication with the public about fluoridation. First, to the extent that the public consults the scientific literature, it is essential that the methodological limitations of a study, as well as its relevance to community water fluoridation, be widely and promptly communicated. Second, scientific evidence is only one component of why some people support or do not support fluoridation, and communication strategies must accommodate that reality.


OBJECTIFS: Examiner les dangers et les risques perçus de la fluoration discutés sur les tribunes en ligne portant sur l’arrêt et les répercussions de la fluoration à Calgary, plus précisément: 1) quels dangers et risques on mentionne; 2) pour ces dangers et risques, quels genres de données probantes on cite; 3) la mesure dans laquelle on cite des articles scientifiques, et leur qualité; et 4) pour un sous-ensemble de dangers et de risques, ce que l’on sait d’après la littérature scientifique en général.

Méthode: Nous avons repéré les commentaires en ligne pertinents au moyen de recherches en texte libre sur Internet, et nous en avons extrait ceux qui traitent explicitement des dangers ou des risques de la fluoration de l’eau. Nous avons identifié les types d’éléments probants mentionnés et examiné les communications scientifiques citées. Enfin, nous avons examiné et résumé la littérature scientifique en général sur deux de ces dangers ou risques.

SYNTHÈSE: Nous avons cerné 17 groupes distincts de dangers et de risques pour les systèmes et appareils du corps humain, pour l’environnement et pour les organismes non humains. Le plus souvent, aucune donnée probante n’était citée. Lorsqu’on citait des données probantes, elles pouvaient être attribuées à des personnes considérées comme des autorités ou à des expériences personnelles. Il était rare que l’on fasse référence à des articles scientifiques, et ces articles (n = 9) présentaient des problèmes méthodologiques importants. Notre examen de la littérature scientifique sur le fluorure par rapport 1) au fonctionnement de la thyroïde et 2) au phytoplancton a mis au jour quelques effets néfastes du fluorure à des concentrations supérieures aux niveaux maximum recommandés (>1,5 ppm).

CONCLUSION: Nos constatations ont des conséquences pour la communication avec le public au sujet de la fluoration. Premièrement, dans la mesure où le public consulte la littérature scientifique, il est essentiel que les contraintes méthodologiques d’une étude, ainsi que sa pertinence pour la fluoration municipale de l’eau, soient largement et rapidement communiquées. Deuxièmement, les preuves scientifiques ne sont qu’une des raisons pour lesquelles certaines personnes sont pour ou contre la fluoration, et les stratégies de communication doivent tenir compte de cette réalité.

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Correspondence to Paulina C. Podgorny BHSc.

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Acknowledgements: P. Podgorny acknowledges her support through an O’Brien Centre Summer Studentship (OCSS) from the University of Calgary. L. McLaren holds an Applied Public Health Chair funded by the Canadian Institutes of Health Research (Institute of Population and Public Health; Institute of Musculoskeletal Health and Arthritis), the Public Health Agency of Canada, and Alberta Innovates - Health Solutions. We are grateful to Diane Lorenzetti, Research Librarian, Department of Community Health Sciences, University of Calgary; and to Lorraine Toews, Librarian, Veterinary Medicine and Bachelor of Health Sciences, University of Calgary, for their expertise and assistance with the literature searches.

Conflict of Interest: None to declare.

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Podgorny, P.C., McLaren, L. Public perceptions and scientific evidence for perceived harms/risks of community water fluoridation: An examination of online comments pertaining to fluoridation cessation in Calgary in 2011. Can J Public Health 106, e413–e425 (2015).

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Key Words

  • Fluoridation
  • drinking water
  • safety
  • risk
  • evidence-based practice
  • public health

Mots Clés

  • fluoration
  • eau potable
  • sécurité
  • risque
  • pratique fondée sur des éléments probants
  • santé publique