For the first time in more than 50 years, the federal government has recommended lowering the level of fluoride in drinking water.

Since 1962, the Department of Health and Human Services (DHHS) suggested that public tap water contain between 0.7 and 1.2 milligrams of fluoride per liter. But on Monday, the department said now it’s recommending that the level not exceed 0.7 milligrams per liter (which is the same as 0.7 parts per million, or ppm). The announcement comes as no surprise; the DHHS first proposed making this change in 2011, and most large cities have already lowered their fluoride levels accordingly.

Water utilities add fluoride to the taps of two-thirds of Americans for the purpose of reducing cavities. Higher levels of fluoride have been shown to increase the risk of dental fluorosis, a staining of the teeth. Mild cases lead to white spots, while more severe ones can cause brown stains and mottling. The most recent data shows that 41 percent of American adolescents between the ages of 12 and 15 have some form of fluorosis, a number that continues to rise, according to the Centers for Disease Control and Prevention.

The DHHS said in a statement on Monday that the move should reduce the chance of developing fluorosis while still helping to prevent cavities. When the 0.7 to 1.2 ppm recommendation was first made, there were fewer sources of fluoride.

“While additional sources of fluoride are more widely used than they were in 1962, the need for community water fluoridation still continues,” said Deputy Surgeon General Rear Admiral Dr. Boris Lushniak. “Community water fluoridation continues to reduce tooth decay in children and adults beyond that provided by using only toothpaste and other fluoride-containing products.”

The American Dentistry Association and public health researchers lauded the announcement. But some don’t think it goes far enough.

Fluoridation first began in 1945 in Grand Rapids, Michigan, and there is evidence that the practice helped reduce cavities when the mineral wasn’t widely available in toothpastes and rinses, among other things. But there hasn’t been enough research done in recent years to show that it is still necessary, says Dr. Philippe Grandjean, an environmental health researcher and physician at Harvard University.

“We need to revisit those benefits to make sure that the old reports are still valid for the current fluoride exposure situation,” Grandjean says.

He advocates using fluoride topically (e.g. brushing your teeth with toothpaste), as opposed to swallowing it and subjecting all of the body’s organs to the chemical. It became clear around 1999 that fluoride primarily acts topically and needn’t be swallowed to be effective. He also noted that cavity rates have declined at similar rates in countries with and without fluoridation.

More recent research indicates that fluoridation may have unforeseen negative health effects. Studies published this year have suggested a link between fluoridation and attention deficit hyperactivity disorder, as well as an underactive thyroid. Scores of studies, mostly done in China, have also shown that high levels of naturally occurring fluoride in water harm brain development and reduce IQ.

“I’d say it’s a reasonable concern that fluoride can affect brain development,” Grandjean says. “Lowering the recommended fluoridation level to 0.7 mg per liter is very well-justified. I would in fact recommend that the level be reduced even further.”

The new recommendations have been published [PDF] in Public Health Reports.

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