Second thoughts about fluoride.

L ong before the passionate debates over cigarettes, DDT, asbestos or the ozone hole, most Americans had heard of only one environmental health controversy: fluoridation. Starting in the 1950s, hundreds of communities across the U.S. became embroiled in heated battles over whether fluorides—ionic compounds containing the element fluorine—should be added to their water systems. On one side was a broad coalition of scientists from government and industry who argued that adding fluoride to drinking water would protect teeth against decay; on the other side were activists who contended that the risks of fluoridation were inadequately studied and that the practice amounted to compulsory medication and thus was a violation of civil liberties. The advocates of fluoride eventually carried the day, in part by ridiculing opponents such as the right-wing John Birch Society, which called fluoridation a communist plot to poison America. Today almost 60 percent of the U.S. population drinks fluoridated water, including residents of 46 of the nation’s 50 largest cities. Outside the U.S., fluoridation has spread to Canada, the U.K., Australia, New Zealand and a few other countries. Critics of the practice have generally been dismissed as gadflies or zealots by mainstream researchers and public health agencies in those countries as well as the U.S. (In other nations, however, water fluoridation is rare and controversial.) The U.S. Centers for Disease Control and Prevention even lists water fluoridation as one of the 10 greatest health achievements of the 20th century, alongside vaccines and family planning. Now, though, scientific attitudes toward fluoridation may be starting to shift in the country where the practice began. After spending more than two years reviewing and debating hundreds of studies, a committee of the National Research Council (NRC) released a report in 2006 that gave a tinge of legitimacy to some longtime assertions made by antifluoridation campaigners. The report concluded that the Environmental Protection Agency’s current limit KEY CONCEPTS