In a study spanning nearly 90 years of testing, Iowa’s groundwater fluoride levels ranged from barely traceable to more than 11 milligrams per liter, far above the federal guideline, according to University of Iowa researchers.
The September study conducted by UI researchers found that, across the state, fluoride levels in groundwater ranged from below 0.1 to 11.2 mg/L, with a median of 0.35 mg/L. The study, however, only reported its objective observations and did not conclude why the variance
is so wide.
In the study, researchers say such extremes from too little or too much fluoride could have important health implications, as low levels reduce protection against cavities while high levels can damage teeth and bones. Some cities add fluoride in drinking water.
While Johnson County wasn’t singled out in the study, the U.S. Center for Disease Control’s monthly fluoride report revealed that from 2019 to 2024, the Iowa City Water Department sat comfortably at 0.71 mg/L over the past six years.
The U.S. Public Health Service recommends an optimal fluoride concentration of 0.7 mg/L in order to prevent tooth decay while minimizing the risk of dental fluorosis, a condition caused by excessive fluoride ingestion that can lead to severe discoloration, deep pits on the teeth, and structural damage to teeth.
The findings come amid a growing national debate over the safety and benefits of water fluoridation. As of October, both Utah and Florida have banned the chemical in drinking water to the disapproval of the American Dental Association.
Johnson County Public Health Director Danielle Pettit-Majewski said overall, Iowa is a dental care desert.
Last year, 22 percent of kids aged 0–20 years old receiving an oral screening by I-Smile in Johnson County had tooth decay.
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As for the entire state, 87 of Iowa’s 99 counties have been marked as dental shortage priorities needing closer access to dental resources, according to Delta Dental of Iowa.
“We don’t have a lot of access to dentistry in the state, especially for folks who are low income,” Pettit-Majewski said. “Water fluoridation is a safety net for all of our populations who are drinking fluoridated water because it protects the enamel on their teeth.”
In the UI study, the Manson region of north central Iowa was particularly analyzed.
The Manson region had the highest concentrations of fluoride throughout the nearly 90-year period. Wells within 50 kilometers of the Manson region had an average fluoride concentration of 0.81 mg/L.
Overall, 69 percent of the total samples fell below the optimal 0.7 mg/L, while 7 percent exceeded the Environmental Protection Agency’s, or EPA, secondary limit of 2 mg/L.
The secondary limit is a unenforceable guideline set by the EPA to prevent fluoride from reaching above 2mg/L, which can cause mild dental fluorosis.
Only 0.4 percent of the groundwater samples exceeded the maximum containment level of 4 mg/L, a limit enforceable by law and one that, if ignored, could cause severe dental fluorosis.
Darrin Thompson, associate director of UI’s Center for Health Effects of Environmental Contamination and a coauthor of the study, said most current fluoride research only paints a picture of fluoride levels on the national level.
“Here, we wanted to look at what this means for Iowa and what that concentration looks like historically so that readers can be better informed about potential risks,” he said. “The general theme is that Iowa overall has typically very low levels of fluoride.”
Thompson hopes the study can also assist private well owners, as between 230,000 and 290,000 Iowans rely on a private well for their drinking water supply, according to the Iowa Environmental Council.
“Testing a private well is the responsibility of the owner,” he said. “You can look at the maps of the aquifers and well depths [in the study] that may be of concern. And if you have a concern about fluoride, use that to either seek out testing or seek out treatment to meet
your needs.”
Stuart Cooper is the executive director of the Fluoride Action Network, an organization working to promote the avoidance of fluoride due to its potential harmful effects. He said he believes the 7 percent of samples found exceeding the secondary limit are worrisome, but the U.S. overall has safer fluoride levels than the rest of the world.
“There are countries like India and China that have a lot of naturally occurring fluoride in the drinking water,” he said. “And it is an epidemic, people have skeletal fluorosis. They’re hunched over, they have brittle bones. Their lifespan is dramatically short, and they have a difficult time filtering it out.”
In the U.S., Cooper said there is still much to be done for alerting residents of higher fluoride levels, as most notices for high local fluoride concentrations are only found in the water bill.
Cooper said there is still room to be worried about the health risks of fluoride before it begins to exceed the EPA’s maximum containment level.
He cited JAMA Pediatrics, a monthly peer-reviewed medical journal published by the American Medical Association, and their meta-analysis published in January, which found fluoride exposure above 1.5 mg/L is associated with lower IQ scores in children.
Cooper said this could especially be a problem for mothers who use infant formula with tap water.
“A child who consumes infant formula with fluoridated water has an increased risk of lowered IQ by an average five IQ points,” he said. “This comes with additional neurobehavioral disorders, lower executive function, and also a whole host of other issues, like kidney, liver, and endocrine disruption.”
Cooper also cited a National Research Committee report in 2006, which claimed that the maximum containment level and the secondary maximum containment level are not protective of public health.
The study did not evaluate or oppose the 0.7 mg/L level used in community water fluoridation programs.
“So here we are, and that’s the need,” Cooper said. “Neither have ever been lowered for political reasons because the public will lose trust. You can’t call something the greatest public health achievement of the 20th century and all of a sudden walk it back.”
Steven Levy, a professor in the UI College of Dentistry and a coauthor of the study, said the JAMA Pediatrics meta-analysis used by critics of fluoride was scientifically faulty.
Levy said the meta-analysis grouped very high fluoride levels from other countries like China and India into the study, which host a myriad of additional contaminants in their waters. The meta-analysis also grouped many tropical areas areas that reported drinking three to five times as much water.
“Unfortunately, those scientists didn’t do a good job scientifically on that. They put it all together to try to exaggerate the risks by not separating things,” he said.
Levy and his colleagues are currently working on another analysis of the meta-analysis.
Levy said when water fluoride is naturally occurring, it is tested less frequently. When it is artificially adjusted water fluoride, it is tested daily and reported to the state and the Centers for Disease Control.
“So we want to reassure people that even though there’s different sources and different mixes and different situations of naturally occurring versus adjusted fluoride, it’s all monitored very carefully,” he said.
Pettit-Majewski said fluoride helps prevent far more than cosmetic deficiencies on the teeth.
Damage to tooth enamel can lead to gum inflammation and allow bacteria to enter the bloodstream, potentially contributing to serious health issues, such as heart disease, diabetes complications, and even miscarriages, Pettit-Majewski said.
“Our mouths are an opportunity for infection to travel to the rest of our body,” she said. “Children who are struggling with cavities have a difficult time eating, they might have a difficult time sleeping, they might have a difficult time learning or paying attention in class because they are in pain.”
Becky Hackett-Leas, the oral health coordinator of Johnson County Public Health, said no community is adding excessive fluoride to the point of the EPA’s maximum containment level.
While the study revealed that 7 percent of the groundwater samples exceeded the EPA’s secondary limit of 2 mg/L, 99 percent of the actual drinking samples remained below 2 mg/L.
“There is not a fluoride advocate across the nation that advocates for 4 mg/L of fluoride,” Hackett-Leas said. “We are really talking about that balance, not too little, not too much. Just like anything else in our diet, we need to keep things at an even scale.”
Original article online at: https://dailyiowan.com/2025/11/04/ui-study-finds-large-fluoride-gaps-in-iowas-groundwater-amid-national-debate/