Robert F. Kennedy Jr. waded into another scientific debate on Saturday by saying Donald Trump’s administration would advise that fluoride be removed from the country’s water supplies if the former president wins Tuesday’s presidential election.

“On January 20, the Trump White House will advise all U.S​. water systems to remove fluoride from public water. Fluoride is an industrial waste associated with arthritis, bone fractures, bone cancer, IQ loss, neurodevelopmental disorders, and thyroid disease,” Kennedy, a former independent presidential candidate, wrote in a social media post.

Trump has suggested that Kennedy, who was an environmental lawyer before entering politics, would oversee a health portfolio in his next administration.

At a campaign rally in New York last week, Trump said he would let Kennedy “go wild on health,” “go wild on the food” and “go wild on medicines.” At a rally in Michigan on Friday, Trump said Kennedy would “have a big role in health care” and has “some views that I happen to agree with very strongly.”

Here’s what health experts are weighing as the public health practice of adding fluoride to America’s water supply comes under increased scrutiny.

What is fluoride?

Fluoride is found naturally in the environment in water and rocks, as well as in some foods. The mineral can also be a byproduct of some industry, according to the CDC.

Why is fluoride controversial?

A federal judge in September ordered the US Environmental Protection Agency to take additional measures to regulate fluoride in drinking water because of a possible risk that higher levels of the mineral could affect children’s intellectual development.

US District Judge Edward Chen ruled that while it’s not clear whether the amount of fluoride typically added to water is causing a drop in IQ in kids, there’s enough risk to warrant investigation and that the EPA needs to take further action in regulating it. The ruling did not state what actions the EPA needs to take and the agency is currently reviewing the decision.

What we know about fluoride’s impact on IQ

A federal review published in August by the National Toxicology Program at the National Institutes of Health concluded higher levels of fluoride are linked to lowered IQ in children.

The program based its conclusion on studies involving fluoride levels at about twice the recommended US limit for drinking water.

However, the review also noted exposure levels at lower levels was less definitive: “The evidence of an association between fluoride exposure below 1.5 mg/L and lower IQ in children appeared less consistent than results of studies at higher exposure levels.”

Previous research has also found higher levels of fluoride exposure during pregnancy were associated with declines in IQ in children.

A 2019 study looking at Canadian mothers and children found for each additional 1 milligram per liter in concentration of fluoride in a mother’s urine, there was a 4.5-point drop in IQ in males. The study did not find such a significant association in female children, nor did it examine why boys were more significantly affected.

What we know about fluoride and health

The US Centers for Disease Control and Prevention recommends community water fluoridation as a cost-effective way to improve Americans’ oral health.

Exposure to fluoride above the public health recommended amount over many years can result in skeletal fluorosis, a condition that is rare in the US and that causes weaker bones and joint pain. Too much fluoride can also lead to dental fluorosis, which is cosmetic and can lead to the outer enamel layer of the tooth to have white specks or lines.

Recent research examining the link between cancer and fluoride levels has not found an association, according to the CDC and the American Cancer Society.

There also isn’t any evidence that fluoride can cause birth defects in humans, according to the CDC.

Why is fluoride in our water supplies?

The mineral can help prevent tooth decay by strengthening the protective outer layer of enamel that can be worn away by acids formed by bacteria, plaque and sugars in the mouth. Adding fluoride to public water systems first started in the United States in 1945.

Now, nearly three-quarters of the US population — about 209 million people — are served by drinking water systems that have been fluoridated, according to CDC data.

State and local governments control most of the water supplies in municipalities across the country. Some communities throughout the country, such as Portland, Oregon, and Tucson, Arizona, have voted to opt out of adding fluoride to their water.

Why is fluoride in our water if we have it in our toothpaste?

Recently, the public health practice of adding fluoride to water supplies faced new scrutiny after some reports suggested the benefits may not be as significant as they once were, especially with the widespread use of toothpaste that includes fluoride, which has been available since the 1970s.

Last month, a report from the Cochrane Collaboration, an independent group that systematically analyzes scientific research, found only a slight benefit in adding fluoride to tap water, leading to slightly fewer cavities in children’s baby teeth.

Other studies determined that fluoride in water led to a difference of decay in only about a quarter of a tooth, on average, according to Cochrane report.

However, the American Dental Association says fluoride in community water supplies is “the single most effective public health measure to prevent tooth decay.”

“Studies prove water fluoridation continues to be effective in reducing dental decay by at least 25% in children and adults, even in the of era widespread availability of fluoride from other sources, such as fluoride toothpaste,” the ADA says on its website.

The CDC continues to promote the safety and benefits of community water fluoridation.

“Water fluoridation has been identified as the most cost-effective method of delivering fluoride to all members of the community regardless of age, educational attainment, or income level,” the agency wrote in a statement in May.

If you’re worried about your fluoride intake, you can switch to bottled water, look for water filters that filter out fluoride and make sure your kids don’t swallow their toothpaste.