A new U.S. government report has sparked debate over the safety of fluoride levels in drinking water. The report concludes that children exposed to fluoride at twice the U.S. recommended limit (0.7 milligrams per liter) may face a higher risk of lower IQ scores. Essentially, this means excessive fluoride may negatively impact cognitive ability.

The report, released by the National Toxicology Program (NTP) under the Department of Health and Human Services, is the first of its kind to link high fluoride exposure to potential neurological effects in children with “moderate confidence.”

The analysis is based on a review of studies conducted in various countries, including Canada, China, and India. It suggests that fluoride levels above 1.5 milligrams per liter in drinking water could be associated with a decline in children’s IQ.

“Many substances are healthy and beneficial when taken in small doses but may cause harm at high doses. More research is needed to better understand if there are health risks associated with low fluoride exposures,” the authors wrote in the report.

The benefits of water fluoridation

The practice of adding fluoride to public water supplies, known as water fluoridation, has been a significant public health initiative since the mid-20th century. The origins of water fluoridation trace back to the early 1900s. Scientists noticed that people living in areas with naturally high fluoride levels in their water had fewer cavities. This observation spurred further research, culminating in the pioneering study in 1945 in Grand Rapids, Michigan, where fluoride was added to the city’s water supply.

This experiment marked the world’s first instance of deliberate water fluoridation. And the results were striking: the city experienced a significant reduction in dental caries among children. These findings sparked a movement across the United States and eventually the world to adopt water fluoridation as a standard public health practice.

Fluoride, a naturally occurring mineral, helps to prevent tooth decay by strengthening tooth enamel. It makes enamel more resistant to acid attacks from bacteria in the mouth. When fluoride is ingested in small amounts through drinking water, it becomes incorporated into the developing tooth structure of children, providing lifelong benefits. Additionally, fluoride helps to remineralize areas of teeth that have been weakened by decay, reversing early damage. This dual action of both prevention and repair makes fluoride particularly effective as a tool against tooth decay.

The benefits of water fluoridation are well-documented and widely recognized by major health organizations. Among these are the World Health Organization, the Centers for Disease Control and Prevention (CDC), and the American Dental Association. Studies consistently show that communities with fluoridated water have lower rates of tooth decay across all ages.

For every dollar invested in fluoridation, communities can save an estimated $38 in dental treatment costs. Thus, it is one of the most economically efficient preventive health strategies available. In fact, the CDC considers water fluoridation one of the top ten public health achievements of the 20th century due to its profound impact on reducing dental caries — a condition that affects nearly everyone at some point in their lives.

However, fluoride’s story is more complex.

How much is too much?

While the mineral helps to strengthen teeth and prevent cavities, too much fluoride can cause dental fluorosis. The condition presents as discoloration and splotches on teeth. In response, the federal government lowered its recommended level of fluoride in drinking water to 0.7 milligrams per liter in 2015.

The new NTP report suggests that the risk may extend beyond teeth, potentially affecting brain development. Previous studies have hinted at this connection, but the government’s acknowledgment brings new weight to the debate over fluoridation.

The report did not offer a solid figure in terms of how many IQ points might be lost. However, some of the studies cited in the report offer a range of 2 to 5 IQ points. The report did not quantify the relationship between fluoride and cognition in adults, nor did it investigate the effects of too little fluoride in water.

Currently, about 0.6% of the U.S. population — around 1.9 million people — access water from systems with naturally occurring fluoride levels at or above 1.5 milligrams per liter. The new findings raise questions about whether additional measures are needed to protect these populations.

The complex relationship between fluoride and the brain

So, how does fluoride potentially affect the brain? Scientists hypothesize several mechanisms. One idea is that fluoride could interfere with the functioning of the central nervous system. Animal studies have shown that high levels of fluoride exposure can lead to oxidative stress in the brain. Such stress can damage neurons and other essential cellular structures. Another hypothesis is that fluoride might alter calcium signaling in the brain. This signaling is crucial for many cognitive processes, including learning and memory. Critically, these effects appear to be dose-dependent.

While the report provides a significant step in understanding fluoride’s potential neurological effects, it stops short of recommending specific policy changes. The American Dental Association, previously a strong supporter of water fluoridation, has not yet fully responded to the findings.

Given the preliminary nature of these findings, experts call for more research to better understand the relationship between fluoride exposure and IQ levels. Some researchers suggest that pregnant women might want to reduce their fluoride intake, not only from water but also from certain teas that are high in fluoride.

We still don’t know the exact thresholds at which fluoride transitions from being a friend to a foe of public health. As the debate unfolds, the public and health officials alike must weigh the benefits of fluoride for dental health against potential risks for brain development.