Australian health authorities are reviewing the case for fluoride in drinking water amid concerns scientific evidence supporting the benefits and risks to people’s health may have shifted.
While most Australians have been regularly consuming low amounts of fluoride since it was added to drinking water in the 1960s and 1970s to prevent tooth decay, several controversial studies in recent years have suggested the mineral may be linked to low intelligence in children and thyroid problems that can cause weight gain, fatigue and depression.
On Tuesday, the National Health and Medical Research Council revealed that a 2012 study linking very high levels of fluoride to low IQ among some Chinese children prompted it to commission a new review of the health effects of the celebrated public health intervention.
A spokesperson for the NHMRC said while the Chinese study increased concern about the safety of fluoride and potential neurotoxicity for children, it was conducted in a country with very different naturally occurring levels of fluoride that are not seen in Australia, meaning “care needs to be exercised in interpreting the results”.
Furthermore, the study published in the journal Environmental Health Perspectives identified drinking water with fluoride concentrations up to 11.5 mg/ L in China. In Australia, the recommended level is 0.6-1.1 mg/L.
Nonetheless, the NHMRC established a fluoride reference group last year and has commissioned Sydney University researchers to assess new evidence by mid 2015. A draft statement on their findings is due by the end of the year.
Until then, the NHMRC says its 2007 review of fluoridation stands, showing it is safe and effective for preventing tooth decay and that there is insufficient evidence to support any other “measurable harm to human health”.
“The only potential harm associated with water fluoridation is dental fluorosis [mottles or flecks on the teeth], and this can be minimised by the careful regulation of the concentration of fluoride in fluoridated water at levels aimed to prevent tooth decay,” the spokesperson said.
But on Tuesday, British researchers called for health authorities to reconsider its water fluoridation program after a new study linked fluoride to higher rates of hyporthyroidism – low thyroid function that slows the metabolism down and can cause fatigue, weight gain and depression.
The observational study published in the Journal of Epidemiology & Community Health (a specialist journal published by the British Medical Journal group) reported that GP clinics in areas with fluoridated water were twice as likely to report high rates of hypothyroidism compared with clinics in areas without water fluoridation.
While the researchers did not prove fluoride was causing the illness, they said their results should be “substantial cause for public health concern” and should prompt people to be tested for the condition.
But David Coggon, professor of Occupational and Environmental Medicine at University of Southampton, said the study was highly questionable.
“As epidemiological evidence goes, this is about as weak as it gets”.
“It is quite possible that the observed association is a consequence of other ways in which the areas with higher fluoride differ from the rest of the country. There are substantially more rigorous epidemiological methods by which the research team could have tested their idea,” he said.
A spokesman for the Department of Health in Victoria said: “The addition of fluoride to drinking water supplies is universally supported by all leading health authorities.”
In Victoria, 90 per cent of the population has access to fluoridated drinking water supplies.