Fluoridation in Water (Part 1)

In this series, we look at the history, benefits, and safety of water fluoridation. And, we start by looking at the efficacy of adding fluoride to the water supply.

A meta-analysis of all the studies on the dental health implications of vegetarian diets showed significantly fewer decayed teeth, missing teeth, and the number of teeth with fillings. One of the studies that bucked the trend and showed that vegetarians had more cavities blamed the excess decay on the fact that vegetarians were significantly less likely to choose fluoride-containing toothpaste, supported by the fact that those who did use toothpaste with fluoride had significantly fewer decayed teeth than those who didn’t.

Fluoride is thought to protect teeth by improving the intrinsic stability of the mineral structure of dental enamel. A recent meta-analysis of nearly 100 randomized controlled trials of fluoride toothpaste involving more than 10,000 people found “high-certainty” evidence that toothpaste containing the typical amount of fluoride reduces tooth decay significantly more than non-fluoride toothpaste in both children and adults. But what about the addition of fluoride to the water supply?

A medical consensus of public health authorities around the world has considered water fluoridation at appropriate levels as a safe and effective means to prevent cavities on a community-wide scale. In fact, the CDC, the U.S. Center for Disease Control and Prevention, deemed fluoridation of drinking water as one of the top ten public health achievements of the 20th century. However, community water fluoridation has long been a flashpoint of polemic and polarization. Anti-fluoridation activists underscore that there is no human dietary requirement for fluoride, and argue that water fluoridation isn’t effective enough to justify the costs, which may include health risks.

First, some background before I dive into the controversy. Fluoride is a mineral element in the Earth’s crust that naturally occurs in most water supplies. This is one of the reasons fluoridation has withstood constitutional challenges. Courts have ruled that rather than an added medication, fluoride can be seen as a nutrient found naturally in some areas but not others, and fluoridation of water supplies is a matter of just leveling the playing field––particularly for poor communities who may have limited access to dental care. Fluoridation can be defined as “the upward or downward adjustment of the level of fluoride content in drinking water to an optimal level just enough to prevent cavities but not enough to cause fluorosis,” or cosmetic changes in the teeth.

It all started in 1901 with an investigation into Colorado Brown Stain, “grotesque” brown stains on the teeth of Colorado Springs residents. At the same time, teeth afflicted by the condition were “surprisingly and inexplicably resistant to decay.” After fluoride was identified as the basis for these changes, a nationwide survey of fluoride levels in drinking water in the 1930s led to the discovery that fluoride could reach levels around one part per million without causing serious fluorosis. Hoping to get the best of both worlds, Grand Rapids, Michigan, in 1945, became the first city in the world to fluoridate its water supply. Within 11 years, cavity rates among children in Grand Rapids were reportedly down more than 60 percent, and a fluoridation movement was born. Today, about two dozen countries fluoridate their drinking water. Dozens of others have naturally fluoridated water, or instead add fluoride to milk or table salt.

Fluoridation pushback started almost immediately in the United States. The obsession of Dr. Strangelove’s Colonel Ripper with the purity of his “precious bodily fluids” was based on real-life right-wing Red Scare conspiracy theories that fluoridation was meant to produce “moronic, atheistic slaves” who would bow to the communists.

Today’s social media is also rife with anti-fluoridation messages. Studies have found that 63 percent of Instagram posts regarding fluoride could be classified as anti-fluoride, 64 percent of tweets on Twitter, 99 percent of YouTube videos, and up to 100 percent of fluoride groups and pages found on Facebook were anti-fluoride. Years before COVID, the anti-fluoridation crusade was considered a case study of “digital pandemics of public health misinformation.” In the year before COVID, the first worldwide survey of the crisis of confidence in science of 140,000 people in 140 countries found that only 18 percent of humanity appeared to have a “high” level of trust in science. To my pleasant surprise though, despite so many institutional failures, a 2020 follow-up of the survey found trust in science actually increased after COVID.

Where does the science land on water fluoridation? First, let me address efficacy. The CDC attributes the steep decline in dental decay in the United States in the latter half of the 20th century to water fluoridation. But similar declines were noted in non-fluoridated countries––attributed in large part to the widespread global distribution of fluoride toothpaste. The best evidence we have comes from prospective studies with concurrent controls, comparing cavity rates over time in fluoridated versus non-fluoridated populations. There have been more than 100 such studies to date, and overall, fluoridation results in 35 percent fewer decayed, missing, or filled baby teeth, and 26 percent fewer decayed, missing, or filled permanent teeth. So, community fluoridation does indeed help to cut down on cavities. The question then becomes, at what cost?––which we’ll discuss next.

Naturally fluoridated waters up around two parts per million can put children under the age of nine at increased risk for dental fluorosis, and a lifetime of drinking water at four ppm can cause skeletal fluorosis and increase the risk of bone fractures. You can see these kinds of levels in the Earth’s natural fluoride belts that extend from Turkey through Iraq, Iran, and Afghanistan to China and Japan.

The reason susceptibility to dental fluorosis ends at around eight years old is that’s when enamel maturation is completed, before our final permanent teeth finish erupting. After teeth are formed, dental fluorosis can no longer develop or worsen. At one ppm, one part per million of fluoride, public health authorities estimated that less than 10 percent of kids would develop the condition, and only in its mildest forms. We’ve since learned that the prevalence and severity of fluorosis is much higher than predicted. According to the CDC, about a third of American children now have some form of dental fluorosis, with about one in 30 experiencing a moderate or severe case. This may reflect exposure to multiple fluoride sources not factored in to the original calculations.

Now, most fluorosis is so mild as to be hardly noticeable, taking the form of white streaks or splotches visible only to dentists under the bright lights of their exam chair. But serious cases can involve severe pitting and discoloration, and present more than just a cosmetic defect. For example, one study found that children with severe cases are more likely to be viewed by their peers as less attractive, less careful, less clean, less happy, less healthy, less intelligent, less kind, less reliable, less social. Imagine what that could do to a kid’s self-esteem.

Given the higher-than-expected rates of fluorosis, in 2015, the U.S. Public Health Service reduced the recommended fluoride concentration of drinking water down to 0.7 ppm across the board. Previously, levels were set at up to 1.2 ppm in cooler areas where people tend to drink less water. This change would be estimated to keep the percentage of those developing fluorosis of “aesthetic concern” down to approximately 12 percent.

In terms of other health concerns, until recently, mainstream medicine’s view might have perhaps best been summed up by the final statement in an exhaustive report published by Consumer Reports in 1978: “The simple truth is that there is no scientific controversy over the safety of fluoridation. The practice is safe, economical, and beneficial. The survival of this fake controversy, in the Consumers Union’s opinion, is one of the major triumphs of quackery over science in our generation.” In the last few years, though, there have been growing concerns about the adverse effects of fluoride on brain development, which I’ll address next.

Fluoride had been found to be a developmental neurotoxin in rats and mice, leading to learning and memory deficits, which led to an interest in studying human populations. Starting in the 1980s, reports started appearing in Chinese medical journals that found correlations between areas naturally containing higher fluoride levels in water with lower intelligence among children. Dental fluorosis, the fluoride-induced tooth mottling, is widespread in China, with more than 90 million residents affected, often in small pockets surrounding particular small springs or mountain sources. Researchers took advantage of the fact that even adjoining neighborhoods could have wildly different fluoride exposure, setting up a kind of natural experiment.

Due to limited access to Chinese journals at the time, these studies largely escaped the attention of scientists in the West until a meta-analysis of 16 such studies was published in English in 2008. “Fluoride and Children’s Intelligence: A Meta-analysis” found that children living in areas prone to fluorosis had five times higher odds of developing low IQ than those living in areas with little or no fluorosis. So, here we were, thinking dental fluorosis was just a cosmetic blemish, but it may instead be a visual indicator of intellectual deficits. A subsequent meta-analysis in 2012 including about 10 more studies found that the average intelligence gap between high- and low-fluoride exposure areas was about seven IQ points. By far the largest study, involving thousands of children, found that even at fluoride levels below 1 ppm, higher fluoride levels were associated with a large drop in the chances of developing excellent intelligence (defined as an IQ of 130 or higher). Even very mild fluorosis was associated with less than half the odds of reaching such a high IQ.

By now, there have been more than 50 studies showing an association between higher fluoride exposure and lower IQ. In the latest systematic review and meta‑analysis, 90 percent of the studies published in the last ten years reported a link between high fluoride exposure and reduced intelligence. However, serious caveats are in order.

First, the fluoride concentrations in most of these studies were well above fluoridation levels. In the 2012 meta-analysis, for example, one study clocked concentrations as high as 11.5 ppm, far exceeding the U.S. target of 0.7 parts per million, as well as the average concentration in the United States, which is around 0.8 ppm in municipal water and 0.3 ppm in well water. Now, to be fair, the 11.5 ppm in the meta-analysis was an outlier. The average elevated level was only about two parts per million, and most found associated IQ decrements below the EPA’s upper limit, its Maximum Contaminant Level Goal of four ppm, which is supposed to represent the level “below which there is no known or expected risk to health.”

Some studies showed lower intelligence with fluoride concentrations even down at one to two ppm, with one estimate suggesting the smallest harmful concentration, potentially shaving off a single IQ point, would be down around 0.3 ppm––assuming you drink four cups of water a day, while others suggest it’s too early to be able to calculate a threshold for human neurotoxicity due to insufficient available data.

The second major caveat is confounding. Nearly all of the studies to date have been performed in rural communities in countries like China, Iran, and Mongolia. Areas within these countries with unusually high fluoride levels may be particularly poor and underdeveloped, since relatively rich communities may be more likely to invest in higher-quality drinking water that filters out fluoride, if only to reduce dental fluorosis. High-fluoride water may also be more likely to be contaminated with other neurotoxins. Fluoride exists in water as a negatively charged particle. To maintain electroneutrality, this may pull into the groundwater positively charged particles such as aluminum, arsenic, lead, or mercury. This doesn’t happen in community water fluoridation, since the negative fluoride ions are balanced out in the water treatment process.

Finally, most of the older studies were cross-sectional and ecological, meaning they looked at a snapshot-in-time of group level data, rather than individual-exposures-over-time. Just because a child with low IQ lives in a high-fluoride area doesn’t necessarily mean they or their mom actually drank the water, for example. Ideally, we’d be able to measure individual exposure levels and then follow the kids over time to see if those with higher exposure really do grow up with stunted intellects.