A Dunedin study that cleared fluoride of adversely affecting IQ has been sharply criticised in an academic letter published in the New Zealand Medical Journal.
The letter, by University of Auckland academic psychiatrist Associate Prof David Menkes and two others, says the study failed to properly assess possible IQ effects from fluoride.
The letter says both sides in the heated fluoride debate are known to ”cherry-pick and distort evidence to suit their respective arguments”.
The Dunedin IQ study was cited as evidence in a recent high-profile New Zealand review of fluoride, which had concluded it was safe, the letter said.
It appeared the review ”overstated available evidence” in its use of the Dunedin IQ study.
”Given the importance of the issue, and the numbers of children exposed, exhaustive and impartial evaluation of scientific evidence should be required to inform public policy.”
While it took into account social and economic status, the IQ study had not factored in other things that could affect IQ, such as the disparity between urban and rural children.
”Suburbs with community water fluoridation were mostly in central Dunedin while those without were peripheral; it is thus very likely that unmeasured factors co-vary with suburb.
”For example, most children without community water fluoridation exposure lived in Mosgiel, which borders a farming district and has rural characteristics.
”Rural children, as the authors note, typically have lower IQs than those from urban areas.”
The study also did not factor in the role of breast-feeding, bottle-feeding, fluoride tablets and toothpaste.
Published earlier this year in the American Journal of Public Health, the IQ study drew on data from the Dunedin Multidisciplinary Study.
The IQ study lead author, Dr Jonathan Broadbent, a University of Otago public health dentistry specialist, said when contacted yesterday he would respond to the criticisms in a future edition of the New Zealand Medical Journal.
”We have taken those factors into consideration and found that they did not affect the outcome of the study,” Dr Broadbent said.