If it were to be completed, the new regulation would reduce fluoride levels allowed in water to be packaged at home and bottled water was imported to 0.7 milligrams per liter, reduced t the current standard of 0.8 milligrams per liter allowed by the FDA.
The proposed standard would only apply to bottled water with additional fluoride. Fluoride levels in bottled water that could contain fluoride from source water would not be affected.
But the concerns of some scientists extend far beyond fluorosis.
The effects of behavioral and cognitive health
In particular, Bashash found a reduction in children's scores on intelligence tests for all 0.5 milligram-liter increases in fluoride exposure beyond 0.8 milligrams per liter found in pregnant mother urine. It's not clear whether this research is relevant to the US population, he told CNN.
In Mexico, for example, the government provides fluoride reducing cavity by adding it to salt, not water (as many people avoid drinking tap water).
Still, the findings of his research were "based on a true measure of absorbed fluoride in the body." And a study of Canada (link) presented at last year's conference and studies conducted in China showed that IQ losses were associated with fluoride levels within a similar size regime.
Due to similar fluoride sources, regulations and diet, Canada's findings of urine levels are likely to be similar to American urine levels, says Bashash.
Neurath trusts that the results of a Mexican and Canadian study would normally apply to the United States as "urine fluoride is the best measure of the total amount of fluoride eaten."
Canadian data from the last 15 years has shown that women living in cities with linear water supplies have "double double" urine fluoride concentrations such as women living in non-linear cities. "Fluoride of drinking water is the main source of fluoride of these women," he said.
The effect of antenatal exposure to fluoride on IQ is "very large," Neurath believes. "And on the basis of population, that is very worrying."
The proposed rule may not be sufficient
More than 30% of young people in the study showed moderate to severe dental fluorosis (a further 35% of children showed fewer signs of the condition), a "huge increase" over a survey carried out about a decade before, said Neurath. We believe that the proposed standard is unlikely to reduce dental fluorosis to acceptable levels.
However, he is more concerned. "Dental fluorosis is a visible sign of over-exposure to fluoride, but there are other unknown signs and poor health effects that are much more serious," said Neurath based on Bashash and Grandjean's work.
"Given that fluoride is added to toothpaste to ensure that the enamel surface of the teeth is properly protected from decay, it is not necessary to add to the dietary fluoride intake," he said.
Otherwise, Bashash said that fluoride in drinking water was considered one of the "greatest public health victories" in the prevention of cavities. While he is a scientist to study a particular subject, the work of policy makers is to get a general understanding of what is needed. The FDA looks "in the big picture" by collecting the evidence and evaluating the advantages and disadvantages based on national priorities. "This has been a hot topic for 60 years."
Linda Birnbaum, director of the National Institute of Environmental Health Sciences, explained that a "large cross-government working group" was looking at the data available in 2010 to 2011 and concluded that 0.7 mg / L was an appropriate level of t fluoride concentrate when drinking water, one that balances safety against dental decay while limiting the risk of dental fluorosis.
The organization has funded studies exploring other health effects, he said, "and we are looking at the information in a systematic review now."
The International Bottle Water Association, a trade group, said it supported the FDA's proposal to review the quality of fluoride quality added to bottled water.
"Most companies are far below the" proposed new limit, according to Jill Culora, a spokesperson for the association. " "The proposed rule considers a number of fluoride sources in people's diet and will reduce the risk of dental fluorosis further, while continuing to provide optimal fluoride to help prevent tooth decay."
Causes are not the only concern, says Neurath: "The proposed rule is not sufficient."