A decades-old dental health treatment may soon vanish in the United States. Access to fluoride supplements, prescribed to prevent cavities in children without access to fluoridated water, is now under threat from a controversial move by the U.S. Food and Drug Administration.
The agency announced May 13 that it plans to remove fluoride products that can be ingested by children from the market, citing concerns about potential harm to gut microbes, links to thyroid disorders, weight gain and decreased IQ.
“The best way to prevent cavities in children is by avoiding excessive sugar intake and good dental hygiene, not by altering a child’s microbiome,” FDA Commissioner Martin Makary said in the announcement. He is instructing the agency to evaluate the risks of such supplements, which are typically available only by prescription. The order does not include toothpaste, gels or mouthwashes containing fluoride.
But many health experts strongly disagree with the move. Many states and local governments are contemplating stopping the addition of fluoride to drinking water. In fact, on May 15, Florida became the second U.S. state after Utah to ban adding fluoride to public drinking water. So withdrawing the supplements could mean further decay of oral health, particularly for children and people in rural communities, the experts warn.
“It is a complete mystery to me why they think that this is an appropriate way to make the American public healthier,” says Scott Tomar, a dentist and epidemiologist at the University of Illinois Chicago College of Dentistry. The decision, he says, “is based on some of the flimsiest evidence that I’ve seen.”
Fluoride supplements have been used for decades, Tomar notes, and have proven safe and effective for decreasing cavities. The FDA is leaning on studies in noncomparable settings, such as rural China, where there is high exposure to fluoride from burning coal indoors, he says.
“They’re exposed to fluoride in their food and their drinking water and in the air, in addition to all the other combustion products in that air. And on top of that, they’re in areas with very high levels of fluoride in their contaminated surface water,” Tomar says. “We would never allow that level of exposure, or anything remotely close to that level of exposure, in the United States.”
The American Dental Association has also pushed back, questioning the FDA’s interpretation of the science. “A review of the studies offered … [does] not in fact demonstrate any harmful effects for the concentrations of fluoride prescribed by physicians and dentists.”
Even authors of two of the studies on fluoride’s effect on gut microbes cited by the FDA were surprised.
“There is no convincing evidence to support a stance that fluoride use in childhood has a detrimental effect on microbiome development,” microbiologist Gary Moran of Trinity College Dublin said in an email to Science News. “Specific research on the effects of prescription fluoride drugs on general health and the microbiome would be required in order for us to reach any conclusion on whether their use should be discontinued.”
Caroline Orr, a microbiologist at Teesside University in Middlesbrough, England, agrees. “We welcome more research in this area,” she says. But questioning water fluoridation “doesn’t necessarily sit well with me.… Fluoride is beneficial to oral health, and everything that we’ve seen so far suggests that you’d have to get to very, very high concentrations for it to be detrimental to the gut microbiome.”
Science News talked with Orr and Tomar about fluoride and its effects on health. The conversations have been edited for length and clarity.
How are fluoride supplements used?
Tomar: Fluoride supplements come in both drop and tablet form. They’re intended to be used for children in communities that have little or no fluoride in their drinking water. It’s used to help prevent tooth decay. In most places, they’re prescription items, usually prescribed by either dentists or pediatricians in those communities.
Dosages range from 0.25 milligrams that would be used for the youngest children up to 6 months of age. The highest dosage is 1 milligram, and that’s used for children aged 6 to 16. It’s comparable in terms of the total daily intake to what they would get if they were drinking fluoridated water at 0.7 milligrams per liter.
How does fluoride prevent cavities?
Orr: When your teeth are exposed to fluoride, you get remineralization of tooth enamel. So basically, any minerals that are lost from the teeth are being replaced, and it strengthens them. With that, you get a reduction in the number of cavities, and if there is any tooth decay, then you get a reversal of that as well. Another reason why fluoride is used is that it can be detrimental to harmful bacteria. But the main benefit is that protection of the tooth enamel and the fact that it’s actually strengthening the teeth. That’s a proven benefit.
Does fluoride kill bacteria?
Orr: When it’s in very high concentration, fluoride attacks bacteria by interfering with some of the enzymes that are within the bacterial cell wall. In some doses, it can make the bacteria a bit stressed and just stop them growing. In others, it can kill them. Basically, they can’t perform their usual cellular processes.
There’s not a lot of research on how fluoride kills bacteria. We’ve done some, and we found that you have to get to quite high concentrations of fluoride before you see an impact on the bacteria that you would normally find in the gut and in the mouth. The concentration of fluoride that can kill good bacteria, things like Lactobacilli and Bifidobacteria, is slightly lower than the fluoride concentration that will kill just your kind of average bacteria, but it’s in absolutely nowhere near the level that you would see in fluoridated water. We’re talking about thousands of times the dose of fluoridated water.
What effect does fluoride have on the gut microbiome?
Orr: Every study that we’ve done in the lab and everything that I’ve ever read has showed that that level of fluoride [in drinking water] either has no impact on bacteria or actually has a positive impact on some of the good probiotic bacteria. So as far as water fluoridation goes, there’s no evidence that I’ve ever seen that there’s any real impact on the gut, and certainly not a negative one.
Does fluoride affect IQ?
Tomar: The claims that have been made around water fluoridation and lower IQ are incredibly weak. Almost all the literature cited in the reports that [the FDA] relied on — three-quarters of it — by their own admission, was low quality and at high risk for bias.
The high-quality studies that have been done in countries that have levels of fluoride exposure relevant to the United States — those done in in Denmark, New Zealand, Australia, Spain and Sweden — have found no association with any impact on IQ or neuro development.
Is fluoride associated with thyroid disorders or weight gain?
Tomar: The accusation about it having a poor effect on the thyroid function, that actually has been around for decades, and it’s been pretty widely refuted.
Weight gain is a completely new claim. I’ve never seen any reputable evidence that fluoridation is associated with weight gain. Having been involved in fluorides and fluoridation for more than 30 years, it sounds like the things that I encounter from antifluoridation groups. They throw every disease and condition against the wall and see what sticks. Heart disease and thyroid disorder and kidney function and osteosarcoma. I mean, I’ve just heard all of it throughout my career. And again, there’s almost never good science behind it, and that’s the same with these claims about the gut microbiota and effects on thyroid. The science is just not there.
