Harvard Study on Fluoride & Neurotoxicity: Not What it Seems
In October 2012, Environmental Health Perspectives published an article entitled “Developmental Fluoride Neurotoxicity: A Systematic Review and Meta-Analysis” that noted “the possibility of an adverse effect of high fluoride exposure on children’s neurodevelopment.” Anti-fluoride groups often cite this finding out of context. Here are four important observations that the Campaign for Dental Health research team has made after reviewing the study, often referred to as “the Harvard study” because the first of four authors is with the Harvard School of Public Health.
1. Harvard did not conduct primary research or data collection on this topic. This study is a systematic review and meta-analysis of 27 previously published studies. The quality of the studies under review varied widely, causing the authors to state that “each of the articles reviewed had deficiencies, in some cases rather serious, which limit the conclusions that can be drawn.”
2. The study reviewed data on IQ test scores for children living in areas of China, Mongolia, and Iran where fluoride levels were significantly higher than those of fluoridated public water systems in the United States. The highest levels observed in any of the studies – up to 11.5 mg/L – are more than 10 times higher than the optimal level used in the U.S.
3. The study found a very small difference in IQ test scores between children in the high-fluoride and low-fluoride areas. In addition, the authors acknowledge that the average difference “may be within the measurement error of IQ testing.”
4. The authors call for future research to include more precise data on the children involved and greater confidence that other factors have been ruled out as contributing to differences in IQ test scores. The authors noted, for example, that “reports of lead concentrations in the study villages in China were not available.”
This article describes a complex analysis of heterogeneous studies published over 22 years in several different countries, the result of which is a cautious association between high levels of fluoride exposure and possible reductions in IQ test scores. It is not a conclusive study nor can it be represented as definitive evidence of a link between fluoride and lower IQs in children. Finally, the article has no application to fluoride levels in U.S. community water systems.