Sir, there has been discussion for some years around an association between ingested fluoride and IQ. The alleged association has been questioned in a detailed review from the prestigious National Academy of Sciences, Engineering and Medicine (NASEM), the US equivalent of the UK's Royal Society.
The claims arose from papers published in the period 1995 to 2010 emanating from China but also from India, Mexico and Iran. These studies were severely criticised because:
Their design and methods had serious limitations
They were undertaken in areas where natural fluoride levels in the water are higher than the recommended World Health Organisation upper limit of 1.5 mg/litre
The authors often failed to take into account other significant water borne contaminants, such as arsenic
They also failed to take into account other sources of fluoride intake, from coal used for indoor fires and contaminated grain, practices not seen in many developed countries.
More recently a group of researchers from Canada joined the discussion. Their research is of higher quality but commentators have assessed that it still falls far short of demonstrating a clear association between fluoride in drinking water and IQ and certainly does not demonstrate a causal relationship.1,2,3
The US National Toxicology Program (NTP) reviewed the scientific evidence and, in September 2019, published a draft monograph in which they concluded that: 'fluoride is presumed to be a neuro-developmental hazard to humans'. This draft was then sent to the prestigious National Academy of Sciences, Engineering and Medicine (NASEM) for peer review. In its damning 42-page report, published in March 2020, NASEM finds that the NTP draft review failed to provide adequate support for its conclusions. Furthermore, NASEM was critical of the design and methods of many of the studies reviewed by the NTP as well as NTP's own analysis, summary and presentation of the data. The NASEM review recommended that NTP conducts further work.
Meanwhile, we would refer back to the NHS Website (20 August 2019) commenting on the Green et al. paper:1 'Considerable past research has been conducted into the safety of fluoride, including those conducted by the UK government and other international organisations. Overall, these studies all found that fluoride was not associated with significant health risk, while clearly reducing tooth decay.'
Green R, Lanphear B, Hornung R et al. Association between maternal fluoride exposure during pregnancy and IQ scores in offspring in Canada. JAMA Pediatr 2019; 173: 940-948.
Science Media Centre. Expert reaction to study looking at maternal exposure to fluoride and IQ in children. 19 August 2019.
Meyer J. Questionable study casts a cloud over the 75th anniversary of water fluoridation. STAT (First Opinion). 24 January 2020.