The Food and Drug Administration recently proposed lowering the allowable level of fluoride manufacturers can add to bottled water.
In 1973, FDA established standards of quality for bottled water, including allowable levels for fluoride, based on the Public Health Service's 1962 Drinking Water Standards.
Those standards called for 1.4-2.4 milligrams of flouride per liter of water, depending on the annual average of maximum daily air temperatures.
In 2015, the PHS changed its recommendation to 0.7mg/L for community water systems that add fluoride for dental health.
The FDA now proposes lowering its level to be consistent with the PHS recommendation, since bottled water is often used at home instead of tap water. The 0.7mg/L level "is based on findings from evolving research on optimal concentrations of fluoride that balances fluoride's benefits in preventing tooth decay with its risk of causing dental fluorosis, a condition most often characterized by white patches on teeth," the FDA said in its proposal.
But some scientists think that level is still too high.
"Given that fluoride can damage brain development, I would recommend that the maximum fluoride concentration in bottled water be kept at a lower level than 0.7 mg/L," Philippe Grandjean, an adjunct professor of environmental health at the Harvard TH Chan School of Public Health, told CNN in an email.
And a 2017 study by Morteza Bashash found that pregnant women who were exposed to higher fluoride levels gave birth to children who later were found to have lower IQs and higher incidents of ADHD. Bashash is an assistant professor in the Dalla Lana School of Public Health at the University of Toronto.
The International Bottled Water Association, a trade group, said it supports the FDA proposal to revise the standard of quality for fluoride added to bottled water, CNN reported.
"Most companies are well below" the proposed limit, according to Jill Culora, a spokeswoman for the association. "The proposed rule takes into account the many sources of fluoride in people's diets and will further reduce the risk of dental fluorosis, while still providing an optimal level of fluoride to help prevent tooth decay."
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