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.