A Perspective on Fluoridation

The widespread addition of fluoride ion to community water supplies is again a hot topic. A systematic review by the reputable Cochrane Collaboration recently reported that water fluoridation showed no detectable average anti-caries benefit for adults and a small, albeit measurable, benefit among children.¹ This information comes in the wake of other studies that reported that children from some communities with fluoridated water had lower IQ tests — suggesting that fluoridated water may be at fault. Indeed, a recent systematic review by the Journal of the American Medical Association Pediatrics reported some correlations between fluoridated drinking water and lower IQs.²

It is important to note that the lowest concentration of fluoride that revealed an IQ effect in the latter review was twice the recommended concentration for water supplies in the United States. It is also essential to recall that correlation is not the same as causation. This is because independent variables may escape attention and thus go unconsidered. For example, in springtime Hawaii, the increasing water temperature in a swimming pool correlates positively with the likelihood of Pacific plovers appearing on nearby lawns. But neither causes the other. This is correlation without causality. However, correlations are key clues to causality and can sometimes — even by themselves — be important in the cost (risk) vs benefit evaluations needed for public health decisions.

Understanding how we arrived at water fluoridation is informative. In the early 20th century, dental caries represented a major public health problem. Concurrently, epidemiological studies compared caries rates in communities with high well-water fluoride concentrations to those with minimal fluoride in their drinking water. Despite untoward esthetic effects (increased enamel mottling paralleling increasing fluoride concentrations), higher water fluoride appeared to decrease the incidence of caries. However, not only was overall caries incidence higher in that era, but professional treatment was also more invasive. Treatment ranged from extractions to surgical treatment (fillings), the latter even for incipient caries. Furthermore, dentists were trained to extend surgical debridement and tooth preparation into nearby nondiseased occlusal pits and fissures. Such “extension for prevention” was thought wise because such areas were thought prone to future caries.

In recent decades, the incidence of dental caries has plummeted in most American cohorts. We also now know that less invasive means are available to manage (especially incipient) caries in a country in which most people are using fluoride dentifrices. Yet in the mid-20th century, despite arguments against involuntary mass medication, community water fluoridation gradually became widespread across the US and elsewhere.

Furthermore, in that era, dental and dental hygiene students were routinely taught that fluoridated water (in utero and in childhood) spurred the development of tooth enamel that was more resistant to caries. This claim was later discarded and a replacement narrative evolved that fluoride’s benefits come from topical effects alone.

It’s long been clear that the “therapeutic window” for systemic fluoride is small. Even before community water fluoridation began, enamel mottling was widely reported in communities that had well-water with natural concentrations approaching 10 ppm and higher. Over the years, numerous reports showed enamel mottling in some people, despite much lower concentrations. In this context, it’s also important to know that individuals’ dosages of fluoride ion from community water have never been studied. This may be important because these dosages may vary greatly insofar that some individuals consume little tap water while others consume a lot. This disparity is likely larger now than in the past because of the proliferation of bottled water.

Fortunately, over-fluoridation of community water supplies has been rare. However, in 1992 many residents of Hooper Bay, Alaska, were sickened and one person died when too much fluoride was accidentally added to community water.³

Many decades have now passed since fluoride-releasing molecules were added to dentifrices and mouthrinses. Indeed, in locales where fluoride wasn’t in community water supplies, in the latter half of the 20th century, parents sometimes instructed their children, after brushing, to swallow fluoride-containing toothpaste foam to assure at least some systemic exposure. The anti-caries effects of dentifrices and rinses are limited to topical effects if used as recommended.

Over time, the narrative emerged that it would be wiser to recommend community water concentrations at the low end of the long-recommended range (0.7 to 1.2 ppm). Thus, the long-used 1 ppm standard evolved to 0.7 ppm.⁴

Today, the public health question remains: Knowing what we think that we know, what should we do? Any risk (cost) vs benefit analysis that includes the latest science tempered by decades of experience must include the possibility that community water fluoridation may be slightly helpful to a few while presenting a small chance of harm to a few.

Fluoridating water also increases the price of tap water, albeit not much. Indeed, what balance of costs (risk) vs benefits makes the most sense in the context that adding chemicals to tap water is interpreted as involuntary mass medication by some?

One way to consider this question is to ask ourselves if we had never put fluoride into drinking water, would we start doing so now? In the absence of needed high-quality studies that better delineate benefits vs risks, in my opinion the answer would likely be no.

References

1. Iheozor-Ejiofor Z, Walsh T, Lewis SR, et al. Water fluoridation for the prevention of dental caries. Cochrane Database Syst Rev. 2024;10:CD010856.
2. Taylor KW, Eftim SE, Sibrizzi CA, et al. Fluoride exposure and children’s IQ scores: a systematic review and meta-analysis. JAMA Pediatr. 2025 Jan 6. Online ahead of print.
3. Hulen D. Where the water turned deadly: fluoride system wasn’t the only thing that failed in Hooper Bay. Anchorage Daily News. September 22, 1992. Updated July 16, 2016.
4. United States Department of Health and Human Services Federal Panel on Community Water Fluoridation. Public Health Rep. 2015;130:318-331.

From Dimensions of Dental Hygiene. March/April 2025; 23(2):8-9.