WASHINGTON, D.C.--The Environmental Protection Agency (EPA) should lower the maximum amount of fluoride it allows in drinking water, according to a National Academies of Sciences (NAS) report released here today. An NAS panel found compelling evidence of severe tooth decay in 10% of children exposed to the maximum legal limit--about 4 times higher than what's typically added to drinking water. Most of the panel also felt that adults exposed to such levels over a lifetime were likely to have a higher incidence of bone fractures.
Water suppliers have added fluoride to drinking water in the United States since the 1950s to combat dental cavities. In 1962, the U.S. Public Health Service recommended a concentration of 0.7 to 1.2 parts per million (ppm), depending on how much water people in a given area typically drink. Ironically, children who consume too much fluoride in their first 8 years of life may develop lasting problems with their teeth, including pitting of enamel and tooth decay. Excess fluoride also weakens bones over decades. In addition, some studies have shown that fluoride causes cancer in laboratory animals.
In 1986, EPA set the maximum contaminant level for fluoride at 4 ppm. Seven years later, an NAS panel agreed with this standard, pending further research on uncertainties about exposure and toxicity. But the new panel, chaired by toxicologist John Doull of the University of Kansas Medical Center in Kansas City, came to a different conclusion.
Part of the reason is that the panelists took a more refined look at the tooth condition called enamel fluorosis. Previously, most researchers considered fluorosis a cosmetic problem rather than a health issue. But when the panel considered the most serious consequences--pitting, bacterial contamination, and tooth loss--10 of the 12 members decided that these counted as adverse health effects. And when panel member Charles Poole, an epidemiologist at the University of North Carolina, Chapel Hill, plotted the prevalence of severe enamel fluorosis in 94 studies, he found that the prevalence dropped to near zero when water fluoride levels were below 2 ppm. This and other evidence is enough to justify a new standard, Poole says.
That's not to say that all questions about health effects are settled. The panel found that evidence for cancer effects is "tentative and mixed," but noted that a fairly large study due out this summer should help set future research goals. In addition, follow-up is needed on preliminary findings of endocrine effects in animals and IQ deficits in Chinese populations.
The report, which was 3 years in the making, is winning accolades. "It's very thorough," says toxicologist Tim Kropp of the Environmental Working Group, an advocacy group in Washington, D.C.