A new study published in Proceedings of the National Academy of Sciences (PNAS) has indicated that fluoridated water has no negative effect on IQ or cognitive functioning.
In the study, researchers analyzed data from the Wisconsin Longitudinal Study, which followed 10,317 individuals from the Wisconsin high school class of 1957. Participants were grouped by exposure to community water fluoridation (CWF): 3,614 had no exposure, 2,595 were exposed from birth, 2,087 from age 8, and 2,021 from age 14.
The study examined participants’ exposure to and compared it to measures of IQ at age 16, as well as cognitive performance later in life. It found no evidence that is associated with reduced intelligence or cognitive decline.
The study comes as some US communities have moved to end water fluoridation, citing concerns about potential impacts on brain development. Previous research suggesting a negative relationship between fluoride and IQ has been criticized for focusing on unusually high exposure levels and for lacking representative US-based data.
In contrast, the new analysis used population-representative data and accounted for factors such as family income, parental education and geographic mobility, which could influence both exposure and cognitive outcomes.
Across multiple models, researchers found that individuals exposed to fluoridated water did not perform significantly differently on IQ tests in adolescence or on cognitive assessments later in life compared to those who were not exposed. The results were consistent even when focusing on participants who lived in the same area throughout childhood.
The findings also extend earlier research by examining cognition across the life course, including into older age. Cognitive performance was measured at ages 53, 64, 72 and 80 using standardized assessments.
The authors noted limitations, including the inability to directly measure individual fluoride consumption, such as through biological samples. Instead, the study measured exposure based on ZIP code, since fluoride levels vary by geographic location.
Overall, the study concludes that fluoridated water at levels used in public health programs is not linked to lower IQ or diminished cognitive function.
In 2013, then-Health Minister Yael German (Yesh Atid) ordered the removal of fluoride from water sources not naturally containing the chemical. In 2015, when then-Health Minister Yaakov Litzman (United Torah Judaism) replaced German, he quickly ordered the renewal of water fluoridation.
However, German and Yael Cohen Paran of the Zionist Union party called upon the judicial establishment to halt the fluoridation program, labeling it a violation of citizen’s right to autonomy. The issue was ultimately brought to the Supreme Court, after which Litzman backtracked and let the issue drop. There has been no attempt to fluoridate Israel's drinking water since.
Meanwhile, in the ten-plus years since discontinuing fluoride in tap water, Israeli dentists have observed a significant rise in children’s cavities and have urged its reinstatement, even as some parents remain firmly against the idea.
A study published in September 2024 found a significant increase in dental restorations and crowns among Israeli children ages 3 to 5, attributing the rise to fluoride’s absence. The researchers, from the Hebrew University-Hadassah School of Dental Medicine, concluded that the results provided “further proof of the need to restore community water fluoridation in Israel."
Another study, published in January 2022, analyzed six years of data from dental clinics affiliated with a national Israeli healthcare network, showing that children ages 3 to 12 required nearly double the number of restorative treatments compared to before fluoridation ended. Researchers emphasized that even Israel’s expansion of free dental care for all children failed to offset the worsening dental health.
With fluoridation the subject of widespread misinformation as well as ongoing research, Israel is not the only place to adjust its approach over time. Juneau, Alaska, saw pediatric dental health worsen after eliminating fluoride in 2007, according to a study that examined the cost and frequency of dental treatment for poor children. So did the Canadian city of Calgary, which recorded higher rates of cavity-related treatments under general anesthesia among children after it stopped adding fluoride to its water in 2011. Calgary has now decided to resume fluoridation.
“The success of water fluoridation serves as a beacon for public health in general, and by extension, opposition to it should serve as a warning," Shlomo Zusman, who served as Israel’s chief dental officer for over two decades and was a vocal critic of the 2014 policy change, told the Jewish Telegraphic Agency in December 2024.
He said modern water purification methods mean that fluoridation is far from the only way the modern water supply is altered. In addition, he noted that because 75% of Israel’s potable water is desalinated, it has no natural fluoride levels at all.
“The idea that water without added fluoride is ‘natural,’ as if it comes straight from a spring, is mistaken - there’s no such thing, it’s all manipulated," he said. Referring to a story in the Bible, he added, “The days of Rachel pumping water from the well are long gone.
Zusman dismissed many of the concerns about health risks as a fad, noting, “There was a time when they claimed fluoridation caused hip fractures, then cancer, and later stunted growth in boys" caused by osteosarcoma. “Now the fashion is ADHD and IQ, so they blame fluoridation on that."
“Believe me, if there were serious, professional studies showing harm, I’d be the first to say, stop fluoridating the water," he concluded. “I have eight grandchildren to think of."