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President-elect Donald Trump has chosen Robert F. Kennedy Jr. as his Secretary of Health and Human Services and promised to “let loose on health,” putting health care high on the agenda for his second term .

While we don’t know what the policy will be, Kennedy did indicate what he would look at: the fluoridation of water in the United States. He won’t be able to take action until he is nominated by the Senate in 2025 and then confirmed. But on social media site public water systems, stating: “Fluoride is an industrial waste associated with arthritis, bone fractures, bone cancer, IQ loss, neurodevelopmental disorders and thyroid disease.”

Fluoride is a naturally occurring mineral that is present in trace amounts in soil, plants, water and food, and in optimal amounts helps prevent cavities by keeping teeth strong. Countries use a range of approaches to ensure children receive fluoride. Some countries add fluoride to water, such as the United States, and others add fluoride to milk or salt to keep it at recommended levels. Other countries opt for fluoride varnishes and mouthwashes provided by schools.

Community water fluoridation was introduced in the United States in 1945 to help improve oral health in a cost-effective and equitable manner. The U.S. Centers for Disease Control and Prevention (CDC) named drinking water fluoridation one of the top ten health interventions in America in the 20th century.^e century alongside vaccination, family planning and safer workplaces.

According to figures from the CDC, 72% of the US population will receive fluoridated drinking water by 2022. This varies from country to country, ranging from 8.5% of the population in Hawaii to 100% of the population in Washington, D.C.

Water fluoridation is not mandatory, and while there is a recommended fluoride concentration in drinking water (0.7 milligrams per liter) by the CDC, that level is not an enforceable standard. The decision to fluoridate the water is made at a local level and depends on the amount of fluoride that is naturally present.

There are 36,767 water systems in 36 states with publicly available information on the CDC website, a small fraction of the estimated number of drinking water systems in the US. As of 2023, just over a third (37%) of water systems included in the data are fluoridated.

It also varies depending on the state. In Kentucky, 93.8% of reported water systems are fluoridated, and at the lower end, only 3.7% of reported water systems in Alaska are fluoridated.

There is also a huge range in the levels of fluoride found in these water systems. Not all 36 states reporting fluoride access report fluoride concentration levels, limiting opportunities for in-depth analysis. Among them, 24 states report fluoride levels in 1,774 public water systems.

Approximately 53% of these water systems have fluoride concentrations within recommended levels: between 0.7 mg per liter and 1.2 mg per liter. Just under half of them (47%) have fluoride levels below the CDC’s recommended level.

From publicly available data on fluoride levels in water systems, two water systems, both located in South Carolina, reported fluoride concentrations above WHO guidelines. The WHO states that long-term exposure to fluoride levels above 1.5 milligrams per liter (mg/l) in drinking water can lead to health problems.

It has long been known that fluoride strengthens teeth and bones. That’s why it has been added to food and tap water for decades. The CDC considers community fluoridation responsible for a 25% reduction in cavities in children. Cavities can cause pain and tenderness, which can affect speaking and eating. They can also lead to tooth loss or an infection that can spread to the body and cause serious illness or death.

But at certain concentration levels, fluoride can cause damage. The World Health Organization says that while fluoride reduces the incidence of dental caries (cavities), at higher levels it has negative effects, such as “causing tooth enamel and skeletal fluorosis after prolonged exposure to high concentrations.” Skeletal fluorosis is a serious condition that causes bone weakness and stiffness and pain in the joints.

Numerous studies have shown that fluoridated water can help prevent tooth decay and improve oral health. A 2010 Nevada study found that living in a community with fluoridated drinking water was associated with a lower number of decayed, missing or filled teeth. In 2011, the Canadian city of Calgary removed fluoride from its water due to skepticism about fluoride’s benefits and to save costs. A later study comparing children in the city with those in Edmonton, where the water remained fluoridated, found that children in Calgary had more tooth decay in their baby teeth over three years. This suggests that fluoridated water, without other interventions, was an important source of fluoride for that community.

Still, other studies have shown that improvements in oral hygiene awareness and dental practices in general have reduced the benefits of fluoridated water. A recent report concluded that water fluoridation helps prevent cavities, but not as much as originally thought; authors state that recent improvements in cavity prevention are due to the popularity of fluoride in toothpaste and mouthwash.

International data also support this. Around the world, tooth decay has declined since the 1970s, even in countries where fluoride is not added to water.

Some countries where water is not fluoridated are taking a different approach to oral health and opting for other fluoride-based interventions.

In Britain, for example, Manchester and Blackpool have programs to provide fluoridated milk to local schoolchildren. In the rest of the country, an estimated 10% of the population has access to fluoridated water, either naturally or through local fluoride programs.

In Iceland, water is not fluoridated, but there are fluoride flushing programs in schools across the country. Children who go to school receive a fluoride rinse twice a month.

Japan began a similar fluoride mouthwash program in schools in 1970, which has since expanded to daycare centers across the country. Research has shown that these fluoride mouthwash programs are more effective at reducing cavities when started at a younger age.

In Italy, the Society of Pediatric Dentistry recommends a range of interventions for children, such as brushing teeth twice a day with fluoride toothpaste and reducing sugary foods and drinks. For high-risk individuals, fluoride tablets, varnishes, gels or sealants are recommended, depending on their age.

However, exposure to too much fluoride can lead to adverse effects. A study published in May this year found that higher fluoride exposure during pregnancy was associated with more neurobehavioral problems. And a federal review of existing research in August found that higher estimated fluoride exposure (exceeding WHO guidelines of 1.5 mg/L) was associated with lower IQ in children. These levels are rarely seen in the US.

Water fluoridation is “considered particularly beneficial for underserved communities and families who do not have access or are culturally unwilling to access oral hygiene and dental services,” water researcher John Fawell, a visiting professor at Cranfield University, told me in an e-mail. email to CNN.

Fawell, who has advised the World Health Organization on water quality standards, added: “Fluoride at lower concentrations than (those that cause) dental fluorosis have been associated with a small reduction in IQ in children in some epidemiological studies.

“However, in the absence of a clear mechanism, it remains a relationship that is not necessarily causal.”