Swimming in a (Fluoridated) Sea of Inadequate Data
On the history of fluoride and the new NTP Fluoride and IQ Meta-analysis
A new meta-analysis published in the JAMA Pediatrics suggesting that fluoride is harmful for children’s IQ is making waves. This post takes a longer look at the history of water fluoridation for dental health, the long-time opposition to fluoridation, the evolving but weak evidence on fluoride’s potential hazards, and the failure of the USA research establishment to seriously fund research on environmental exposures throughout key developmental periods.
I did my PhD in Nutrition at Cornell in the city of Ithaca and got my first and only cavity within a few years of living there. While I considered the cavity may have resulted from changing dietary habits (hello, gradschool stress-relieving sugar excursions), I also learned that Ithaca’ water was not fluoridated. I decided to look into the history of water fluoridation in Ithaca and discovered that Clive McCay, a famous nutrition researcher at Cornell (who is credited as one of the first showing that caloric restriction impacts lifespan in rodents) was an OG fluoride skeptic of sorts in the 1950s and 60s when national debates about water fluoridation were ongoing - he expressed concern on a radio program in Ithaca that he was not convinced of fluoride’s benefits to teeth and was worried that there were long-term effects on the thyroid and kidney. Decades later, Ithaca still didn’t have fluoride in the water and I had my first cavity. Thanks, Clive.
The history of fluoride begins with another McKay (though with a K, not C) - Fred McKay was an early 20th century dentist in Colorado Springs who noted that there were brown stains on many of his patients teeth (mottled teeth, now referred to as dental fluorosis) and he suspected it was from something in the water. Others across the globe would report a similar “Rocky Moutain Mottled Teeth” phenotype. McKay would ultimately gather together samples from communities with a high degree of tooth mottling and found that all were high in naturally occurring fluoride , confirming findings in rodents (1931) that was able to reproduce a mottled enamel with added sodium fluoride . The mottling was initially seen as a problem and researchers sought to find alternative water sources and ways to remove fluoride from the water; however, in the course of investigating the cause of the mottling, a dentist and researcher in the UK named Norman Ainsworth would note that in areas where teeth were mottled, they also had less dental decay - providing the first indirect hint that fluoride exposure might be protective against tooth decay. These observations would ultimately lead to a famous ecological investigation called the “21-City Study” conducted by HT Dean, a dentist appointed by the US Public Health Service - the 21 City Study was conducted in 4 states (indiana, Illinois, Ohio and Colorado) across 21 cities where the fluoride and other mineral contents of the water naturally varied. The data from this study was some of the first to indicate that protective effects of fluoride could occur at levels that resulted in minimal mottling (note: this evidence is considered relatively weak ecological data by modern standards)
These early observations would launch a broader effort by health authorities to pilot artificial water fluoridation (i.e. bringing areas with naturally low levels of fluoride up to levels ~1 ppm or 1g/L). Foundational trials in 4 cities receiving fluoridation (vs 4 neighboring ‘control’ cities) were initially selected for a 15 year trial, and 2 additional cities with natural fluoride ~1ppm were also selected to compare artificial vs natural fluoridation to. In 1945, Grand Rapids Michigan would become the first city in the world to artificially fluoridate its water supply (its neighbor city, Muskegon, was its control). By the late 1940s and early 1950s, results from the foundational trials showing lower numbers of cavities in children would roll in, including the Grand Rapids-Muskegon comparisons; the planned 15 yr comparison wouldn’t ultimately happen when Muskegon opted to withdraw from the trial and fluoridate its water. Other trials were also undertaken outside the USA, including ones in Canada, the Netherland, New Zealand, the UK and Ireland, all reporting reductions in tooth decay in artificially fluoridated areas and no major change in control towns. In 1950, The American Dental Association and US Public Health Service endorsed water fluoridation and a large number of cities would adopt this practice (by 1969, 43.7% of Americans were estimated to have access to fluoridated tap water). Optimal fluoride levels for dental health were initally set in the range of 0.7ppm to 1.2ppm, though notably, at this time, fluoridated dental products weren’t quite mainstream, so these levels were established with the idea that water fluoridation was the major source of fluoride alongside the smaller amounts that naturally occurs in foods (Crest technically released the first fluoridated toothpaste in 1956 but these wouldn’t become quite mainstream until the mid 1960s-1970s).
The history of community-level water fluoridation is typically considered a public health success - relatively clear health benefits for dentition were established through quasi-experimental studies and water fluoridation was rapidly taken up (note again: this data is not considered as high quality from modern perspectives; large, randomized cluster trials randomizing many communities to fluoridated water and modeling the data with more advanced statistical methods would be ideal). The success of water fluoridation didn’t occur without some opposition, well beyond Clive McCay’s modest concerns noted above. By 1957, Donald McNeil had written “The Fight for Fluoridation”, detailing the history of fluoride in the USDA and its various opponents, including layfolk, chiropractors, and religious figures. The reasons for opposition for varied, including libertarian style thinking about freedom of choice to consume unfluoridated water, to health concerns with some thinking fluoride is a poison being added to water, with the latter having a subgroup of activists who perceied water fluoridation as a communist plot to take over the country (truly, history loves to repeat itself). Gretchen Ann Reilly wrote an excellent chapter on this titled “Not A So-Called Democracy” in the “The Politics of Healing: Histories of Alternative Medicine in Twentieth Century North America”.
Fluoridation has continued to be a contentious topic, with virtually any and all ails that can affect the human body being ascribed to fluoride since its addition to the water supply. Complaints of fluoride causing teeth to fall out were reported to health officials in Grand Rapids, before the fluoride was actually added to the water. Strident (also phantom) claims around fluoride have existed well into recent history, with a community (Kuopio) in Finland in 1992 complaining of symptoms from water fluoridation during a period that the water fluoridation had unknowing been stopped - a great examples of how the human psyche can influence the perception of health effects and how readily we can be primed to find associations that aren’t causal.
Not all of the concerns about fluoride, however, are total crackpot theories.