Scientists Reveal Exactly How Fluoride in Drinking Water Affects Your Brain Over Decades

Fluoride—an element that’s naturally found in rivers, lakes, and oceans, as well as in some foods and drinks—has been added to drinking water for decades as a way to support dental health. But community water fluoridation (CWF) has come under fire in recent years, with some people alleging that it can be harmful to both your body and your brain.

Now, new long-term research seeks to alleviate a lot of that fear: It found that adding fluoride to water has absolutely no impact on cognition as people get older.

These findings may be especially telling because the study period was so long. While many previous studies looked at the potential effect of fluoride in water over short periods of time, this study, which was published in the Journal of Dental Research, is one of the few to track potential effects of this community health practice across a person’s life.

Here’s what the study found, plus why doctors stress the importance of continuing to add fluoride to community drinking water—despite the recent proliferation of fluoride naysayers.

Meet the experts: Vinay Sharma, Ph.D., M.P.H., lead study author and researcher at Trinity College Dublin; Mark Wolff, D.D.S., Ph.D., dean of the University of Pennsylvania School of Dental Medicine; Jamie Alan, Pharm.D., Ph.D., professor of pharmacology and toxicology at Michigan State University in East Lansing, Mich.; Richard Dupee, M.D., chief of Geriatrics Service at Tufts Medical Center.

What did the study find?

For the study, researchers analyzed data from the Irish Longitudinal Study on Ageing to calculate how much fluoride the 2,495 older adults had likely consumed from having fluoridated water in their lifetime. (Community water fluoridation started in Ireland in 1964.)

The researchers grouped participants by how much of their lives had been spent drinking fluoridated water, ranging from low to high exposure. The participants were also asked to take two standard cognitive tests that are used to assess dementia risk.

After analyzing the data, the researchers found that cognitive test scores weren’t different between the exposure groups. “Lifetime fluoride exposure from community water fluoridation was not associated with later-life cognitive function in older Irish adults, and there was no statistical evidence of effect modification by early-life exposure,” the researchers wrote.

Basically, the practice of community water fluoridation did not seem to affect cognition at all.

“Measuring lifetime exposure lets us capture both the sensitive early years and the cumulative exposure built up over decades,” says Vinay Sharma, Ph.D., M.P.H., lead study author and researcher at Trinity College Dublin. So they looked at how fluoride may impact cognition in childhood along with how it could present itself from a cognitive perspective over time—and found no link either way.

Where did concerns about fluoride come from?

Fluoride has been a hot topic for years, with some folks claiming that the mineral is poisonous. That’s not really accurate, though. It all has to do with the dose.

Too much fluoride can be harmful, but it’s really hard to achieve this amount from drinking water. Specifically, you would have to drink at least five liters of water for every kilogram of body weight at once to have fluoride toxicity, and that’s a toxic amount of water, per the American Dental Association (ADA). That would mean a 155-pound person would need to drink about 350 liters at once to achieve that toxic dose.

Many of the concerns about fluoride’s potential impact on the brain come from a widely debated scientific paper published in 2025 that linked high levels of fluoride in water to lower IQs in children. But there is a big caveat of the paper: It looked at levels that far exceeded what appears in American drinking water.

And there’s scientific support for these new findings, too. A study published in Proceedings of the National Academy of Sciences in April also found no evidence that low levels of fluoride in community drinking water impacted the IQ of children or their brain function later in life.

What are the benefits of fluoride in water?

Fluoride helps to strengthen teeth, explains Mark Wolff, D.D.S., Ph.D., dean of the University of Pennsylvania School of Dental Medicine. That’s why fluoride—which is known as “nature’s cavity fighter”—often appears in oral health products like toothpaste to help protect teeth from decay.

While much of the focus on the benefit of adding fluoride to drinking water focuses on kids’ dental health, there are perks for adults, too, Dr. Wolff says. “Community water fluoride helps the aging population very similarly to the way it helps young individuals,” he says. “The ability to receive fluoride through community water fluoridation has been demonstrated to reduce tooth decay.”

In fact, research has found that adding fluoride to water reduces the amount of tooth decay in young kids by 35%—and by 26% in folks who already have their adult teeth. Fewer cavities means less mouth pain, less painful teeth pullings, and fewer days missed from school or work, per the Centers for Disease Control and Prevention (CDC). What’s more, emerging research suggests a possible link between cavities and systemic inflammation—a process implicated in the development of many chronic diseases.

Public health organizations stress the importance of fluoride in tap water

As the name implies, community water fluoridation is determined on a community level. In the U.S., some states—notably Utah and Florida—have taken steps to ban or severely limit the practice.

But the ADA specifically states this about adding fluoride to water: “Water fluoridation is safe, effective and healthy. Seventy years of research, thousands of studies and the experience of more than 210 million Americans tell us that water fluoridation is effective in preventing cavities and is safe for children and adults.”

The CDC also named the fluoridation of drinking water as one of the 10 greatest public health interventions of the 20th century due to the large decline in cavities since the practice started in 1945.

Doctors aren’t shocked by the latest findings

“This paper adds to the growing evidence that fluoride is safe and does not contribute to cognitive decline at the levels we experience in the water supply,” says Jamie Alan, Pharm.D., Ph.D., professor of pharmacology and toxicology at Michigan State University in East Lansing.

Dr. Wolff agrees. “Studies have not demonstrated cognitive differences as a result of exposure to community water fluoridation at normal community fluoride levels,” he says. “This study very clearly showed that there was no association with normal community fluoride levels.”

There’s also “no convincing evidence that fluoride exposure at the low concentrations recommended for community drinking water adversely affects cognitive function in older adults,” says Richard Dupee, M.D., chief of Geriatrics Service at Tufts Medical Center. “[Fluoride] has not been established as a cause of dementia or age-related cognitive decline.”

But fluoride dose likely matters, too, Dr. Sharma says. “Fluoride levels in Irish public water were set at 0.8–1.0 mg/L for decades, then lowered to 0.6–0.8 mg/L in 2007,” he says. Concerns about fluoride’s effects on cognitive function largely come from communities with naturally high fluoride levels in drinking water—which result in prolonged exposure to amounts well above those used in community water fluoridation programs, he adds. (Fluoride doses in community water in the U.S. vary by municipality, but the U.S. Public Health Service recommends 0.7 mg/L to prevent tooth decay while minimizing potential side effects.)

There are evidence-backed strategies you can use to protect your brain

If you’re concerned about cognitive decline, Dr. Dupee says there are steps to support your brain as you age that have nothing to do with your drinking water. “Cognitive decline is not an inevitable consequence of aging,” he says. That’s why he recommends taking these steps to support your brain health as you age:

• Get regular physical exercise

• Control your blood pressure

• Manage cholesterol levels

• Maintain good sleep habits

• Continue to participate in activities that feel meaningful

“The brain benefits from many of the same healthy behaviors that protect the heart,” Dr. Dupee says. “It is never too late to adopt healthier habits, and even modest changes can make a meaningful difference in maintaining independence and quality of life as we age.”

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