About a year ago, the city of Portland, Oregon was in the news because of its water supply—and not because a teenager decided to relieve himself into a reservoir. Instead, the issue was fluoridation, the addition of trace amounts of fluorine to municipal drinking water. Fluoridation is widespread in the US, as copious evidence indicates it improves oral hygiene.
That evidence prompted the Oregon City Council to approve fluoridation—only to see voters reject that plan by a wide margin. While some of the opposition focused on the finances of the deal for the fluoridation process, concerns about the safety of fluoridation also played a major role in organizing the opposition.
It turns out that a similar drama had been playing out in New Zealand, where the city of Hamilton reversed course on water fluoridation several times over the past two years. Now, in response to the kerfuffle, some New Zealand researchers (combined with a ringer from Duke) have looked into one of the supposed health threats posed by fluoridation: it stunts the mental development of children. Their new report finds no evidence of this, however. In fact, children who grew up with fluoridated water had slightly higher IQs than their peers, though the difference wasn’t statistically significant.