Adding fluoride to the water supply has been hailed as one of the top ten most important public health measures of the twentieth century—but has the practice, introduced in the 1940s to prevent tooth decay in children, now passed its sell-by date?
Two new studies suggest it has, with one concluding there's no such thing as a safe dose of fluoride to the growing body, and another underlining what fluoride's opponents have claimed for years: the chemical is a neurotoxin that affects a child's IQ and ability to learn—even when it's the mother who drank fluoridated water while pregnant.
Advocates of fluoridation have argued that the poison is in the dose. At the recommended concentration of 1 part per million (equivalent to 1 milligram per liter of water), it's safe, they argue.
This is despite the fact that, in 2015, the US Department of Health and Human Services reduced that safe threshold to 0.7 mg, because dentists were reporting a rise in cases of dental fluorosis, a discoloration of tooth enamel caused by excess fluoride.
Fluorosis is on the rise because most toothpastes already contain fluoride—an ingredient they lacked when water fluoridation was introduced. These days, one small strip of toothpaste on a toothbrush has between 0.75 and 1.5 mg of fluoride.
But even this lower level could still be too high, say researchers from Icahn School of Medicine at Mount Sinai in New York—especially as health officials haven't factored in the growing immune system's ability to excrete fluoride. An adult excretes around 60 percent of the mineral, but for a child, this drops to just 45 percent.
Children retain around 55 percent of the fluoride they take in from tap water and toothpaste in their liver and kidneys. Among 1,742 adolescents they tracked, all had high fluoride levels, even though most lived in areas that fluoridated public water well below the 0.7 mg safe level, with some as low as 0.4 mg.1
Compromised kidneys could reduce thyroid gland function, the researchers say, possibly causing hypothyroidism or Hashimoto's disease.
Another possibility is that fluoride that's not excreted could be absorbed by the body's hard and soft tissues, such as the bones and other organs. People with high levels of fluoride in their blood are more likely to develop bone disease, earlier studies have found.
It's been the effects of fluoride on intelligence and learning that are most troubling to many opponents of fluoridation, who point to 54 studies showing that high levels cause a reduction in IQ in people, and 60 animal studies that found fluoride impairs memory and learning abilities.
But a new study has discovered something even more worrying—pregnant women can pass on fluoride to the growing fetus, suggesting it crosses the placenta. Women who drank the most fluoridated water during pregnancy had children who, by the age of four, had lower IQs. There was roughly a four-point drop in IQ score for every 1 mg of fluoride in a liter of the mother's urine.2
Researchers from York University in Toronto analyzed data from 512 mothers and their children, 141 of whom lived in an area with fluoridated water, tracking their levels of fluoride while pregnant and testing the IQs of their children when they reached the age of three or four.
Not surprisingly, the women in fluoridated areas had much higher levels of the mineral in their urine—but they also had more children whose IQ score was below the 107 average for the group.
For every 1 mg of fluoride in the mother's urine, boys' average score was 4.49 points lower, whereas girls didn't appear to be affected by fluoride. This difference has caused critics to dismiss the study as 'bad science,' although one possibility is that the sexes develop differently, and another is that the mother's IQ score has more influence than fluoride on their child's intelligence.
Not so bad
The Canadian study might indeed have been ignored and classified as 'bad science' were it not for the many other studies that have also come to the same conclusion. For example, researchers from the Affiliated Hospital of Guizhou Medical University in China took another look at 26 studies, involving 7,258 children, and concluded that high fluoride exposure in water was strongly linked to lower intelligence levels.3
Other Chinese researchers carried out a similar exercise and came to the same conclusions. They reviewed 27 studies that had compared IQ scores across regions with different fluoridation levels and noted that there was a consistent difference in the scores of children living in areas with the highest and lowest fluoride levels.4
Researchers from the University of Kent in the UK went further, concluding that "fluoride has the potential to cause major adverse human health problems"—and has only a "modest" impact on dental health. The fluoridation of public water should be reconsidered, they say.5
Not so modest
Their last point—that fluoride has only a modest impact in preventing tooth decay—is still hotly debated by the pro- and anti-fluoride camps.
Cochrane, the research body considered an impartial arbiter of scientific data, found evidence that fluoridation reduces dental decay—there was a 35 percent reduction in decayed and missing teeth in children who lived in fluoridated areas—but the reviewers were concerned that the 20 studies they analyzed were old, with small numbers of children and high risk of bias.6
Researchers at Notre Dame University-Louaize in Lebanon also aren't sure. Water fluoridation can be essential in poor communities, but the fact that modern toothpastes and mouth rinses contain fluoride should be enough to prevent tooth decay today, they say. 7
It's not as if we're going to run out of fluoride. It's a form of fluorine, the thirteenth most abundant element in the earth's crust, and it occurs naturally in water and soil. Every time we drink tea or eat seafood that includes edible bones or shells, we're ingesting fluoride—and, of course, we're doing it every day when we brush our teeth with most toothpastes.
It's not a nutrient—although it was heralded as such by dentists in the 1950s—and so there's no recommended daily allowance (RDA) for fluoride; instead there's an "adequate intake" that varies depending on whether you're an adult or a child, man or woman.
The adequate daily dose for a child is 0.7 mg, but Fluoride Action Network, an anti-fluoridation group, argues children get far more than that every day when they brush their teeth or use other dental products. A single strip of toothpaste contains up to 1.5 mg of fluoride, and mouth rinses have 0.25 mg.
Even when public water is fluoridated to the new, lower level of 0.7 ppm, dental fluorosis, a disease caused by an overabundance of fluoride, affects around 12 percent of children, and that figure will be higher in areas where fluoride levels are higher, say the Cochrane researchers.
Water fluoridation may indeed have been one of the top 10 most important health measures in the twentieth century, especially in an age before the affluence we enjoy today, but with increased wealth, awareness of a healthier, low-sugar diet, and the abundance of fluoride toothpastes, it's an intervention of its time, and that time has passed.
No cause-and-effect between fluoride and tooth decay: Three countries—the US, Ireland and Australia—rank among the top 10 for both water fluoridation (left) and tooth decay (right). All in all, there appears to be no correlation between whether a nation fluoridates its water and citizens' dental health. Other factors such as diet and lifestyle are more likely to be involved.
•Small children often swallow 50 percent of the toothpaste on their brush, ingesting up to 1.5 mg of fluoride
•All toothpastes with fluoride are supposed to carry a poison warning in the US
•Almost all the fluoride in our body is in our teeth and bones
•Despite the myth, fluoride doesn't help protect bones affected by osteoporosis; in fact, it increases the chances of fracture
•Fluoride was introduced into public water supplies in 1945 with the promise that dental decay in children would halve. It did—although the rate had already started to drop in 1930
•By 2004, fluorosis—a discoloring of the teeth from excessive fluoride ingestion—was affecting 41 percent of American adolescents
•Almost all research into the effectiveness of fluoride in water was done before 1980
•Just 10 percent of the world's population has fluoridated water