A recent study, Community Water Fluoridation and Intelligence: Prospective Study in New Zealand, published in the American Journal of Public Health, claims to exonerate a link between fluoride and lowered IQ, is scientifically flawed and reveals blatant examiner bias, says the Fluoride Action Network (FAN).
The study’s co-author, pro-fluoridation activist and dentist Jonathan Broadbent, claimed: “Our findings will hopefully help to put another nail in the coffin of the complete canard that fluoridating water is somehow harmful to children’s development.” However, the limitations of Broadbent’s study mean it is inconclusive at best.
Paul Connett, PhD, FAN Executor Director says, “Even if this study was high quality science, which it is not, it could not cancel out over 100 animal and 45+ human studies showing fluoride can cause brain deficits. Broadbent’s research has serious weaknesses.”
1) The study’s small sample size of non-water-fluoridated subjects (99 compared to 891 water-fluoridated subjects) means it has low ability to detect an effect. Even worse, 139 subjects took fluoride tablets, but Broadbent does not say which. Since fluoride tablets are only recommended for children living in non-water-fluoridated areas, there may have been little difference in total fluoride intake between his comparison groups. Broadbent’s failure to consider total fluoride exposure may thus explain why he found “no effect”.
2) Broadbent falsely criticizes 27 previous studies linking fluoride to children’s lower IQ – implying they didn’t adjust for any potentially confounding variables like lead, iodine, arsenic, nutrition, parent’s IQ, urban/rural and fluoride from other sources. In fact, several of the studies did control for these factors. A good example is Xiang’s work, which has controlled for lead, iodine, arsenic, urban/rural, fluoride from all sources, parent’s education, and socio-economic status (SES). Ironically, Broadbent failed to adjust for most of these factors in his own study despite having access to information on many of them.
3) Of the four factors Broadbent did adjust for, most were only crudely controlled. For example, SES was determined solely by the father’s occupation and classified into just 3 levels. Inadequate adjustment for SES could obscure a lowering of IQ caused by fluoride, because almost all of the non-water-fluoridated children came from one outlying town that had lower SES than the fluoridated areas.
“Broadbent is one of New Zealand’s leading political promoters of fluoridation. He is a dentist not a developmental neurotoxicologist,” says Connett. “This single weak study is hardly sufficient to outweigh the substantial body of evidence showing fluoride’s potential to harm the developing brain at relatively low exposure levels.”