Fluoride and IQs
In July 2012, anti-fluoride activists circulated an article from a journal called Environmental Health Perspectives (EHP) to support their claim that fluoride lowers IQ scores in children. There are several reasons why the claim being made by opponents lacks credibility.
- The EHP article reviewed studies on IQ scores for children living in areas of China, Mongolia and Iran where the water supplies have unusually high, natural fluoride levels. In many cases, the high-fluoride areas were significantly higher than the levels used to fluoridate public water systems in the U.S. In fact, the high-fluoride areas in these countries reached levels as high as 11.5 mg/L — more than 10 times higher than the optimal level used in the U.S.
- This article offers a meta-analysis, and its credibility hinges on whether good-quality studies are reviewed. Yet the article’s co-authors admit that “each of the [studies] reviewed had deficiencies, in some cases rather serious, which limit the conclusions that can be drawn.” Although the studies compared high-fluoride with low-fluoride areas, the authors acknowledge that “the actual exposures of the individual children are not known.”
- The two Harvard researchers who reviewed these studies have distanced themselves from the way in which anti-fluoride activists have misrepresented their article. After contacting these researchers, the Wichita Eagle newspaper reported, “While the studies the Harvard team reviewed did indicate that very high levels of fluoride could be linked to lower IQs among schoolchildren, the data is not particularly applicable here because it came from foreign sources where fluoride levels are multiple times higher than they are in American tap water.”
- The Harvard researchers wrote in their article that the average standardized mean difference (0.45) in IQ scores “may be within the measurement error of IQ testing.” Despite web pages claiming that the article ”confirms” that fluoride reduces IQ scores, the Harvard co-authors did not reach a firm conclusion, writing instead that “our results support the possibility of adverse effects …” Indeed, their article called for more and better-quality research, including more “precise” data on the children involved and assurances that other factors have been ruled out as reasons for the IQ differences.
- Given the small difference in IQ scores, it’s possible that arsenic levels, school quality, nutrition, parents’ educational levels or other factors could have shaped the results. The authors also added that “reports of lead concentrations in the study villages in China were not available”— another factor that could not be ruled out. A British research team reviewed similar Chinese studies, found “basic errors” in them, and reported that “water supplies may be contaminated with other chemicals such as arsenic, which may affect IQ.”
- Between the 1940s and the 1990s, the average IQ scores of Americans improved 15 points. This gain (approximately 3 IQ points per decade) came during the same period when fluoridation steadily expanded to serve millions and millions of additional Americans.