Fluoridation of public water supplies to prevent tooth decay has always been contentious, even attracting some very weird scare stories.
The latest prominent opponent of water fluoridation is Robert F Kennedy jnr, the new secretary of health and human services in the United States. But there is very solid convincing evidence that fluoridation is an effective, safe and cost-effective public health initiative. The story was outlined by HI Miller in the American Council on Science and Health in December.
Tooth decay comes second only to the common cold as a physical malady, affecting 60-90 per cent of schoolchildren and almost all adults. It can also lead to serious health complications, eg infections that enter the bloodstream.
Tooth decay can be largely prevented by oral hygiene, professional dental care and a diet low in sugar. But, fluoridation of drinking water is an additional powerful preventive.
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Tooth enamel, largely composed of calcium phosphate arranged in a crystalline structure called hydroxyapatite, is susceptible to erosion by acid secreted by oral bacteria, but the presence of fluoride in water or toothpaste converts hydroxyapatite to fluorapatite and this strengthens tooth enamel. Fluoride also reduces the ability of oral bacteria to secrete acid.
Water fluoridation was introduced in the mid-20th century and is now a cornerstone of public-health policy in many countries, including Ireland. The effectiveness of water fluoridation was first noted in 1901 by dentist Frederick McKay when he observed that the residents of Colorado Springs had unusual mottled and stained teeth (fluorosis) and also displayed remarkably few dental cavities. The tooth-mottling and staining was caused by the naturally high levels of fluoride in the local drinking water.
Subsequent studies showed that communities with concentrations of fluoride in their drinking water higher than one part per million (ppm) have lower levels of tooth decay.
Grand Rapids Michigan was the first city to deliberately adjust public water fluoride concentration to optimum levels and achieved a 60 per cent reduction in dental cavities.
Public water fluoridation in Ireland at a level of 1 ppm was introduced in 1964 by Seán McEntee, minister for health. A selection of countries that fluoridate water supplies (figures in parentheses are the percentage of the general public that receive fluoridated water) includes the United States (73 per cent), Ireland (73 per cent), Australia (80 per cent), New Zealand (61 per cent), Singapore (100 per cent), Brazil, Canada (44 per cent), Chile (70 per cent), Malaysia (76 per cent), Spain (11 per cent) and Israel (70 per cent).
Fluoridation of drinking water is supported by strong evidence and is endorsed by the World Health Organisation and the American Dental Association. The latter estimates that every dollar spent on fluoridation saves $38 in dental costs. Water fluoridation helps poor, underprivileged populations in particular. The incremental health benefits of water fluoridation are smaller in affluent areas where fluoride is widely used in toothpaste.
Fluoridation was opposed from the outset. Opponents called fluoride “rat poison”, claiming it poisons people. Some people even saw fluoridation as a communist plot or a cover-up by the sugar industry to camouflage the dental effects of overconsumption of sugar. For example, the unbalanced air-force Gen Jack D Ripper remarked in the popular 1964 film Dr Strangelove – “Do you realise that fluoridation was the most monstrously conceived and dangerous communist plot we’ve ever had to face?” Such arguments have no credibility and merely reflect ignorance of science and mistrust of authority.
This, of course, is not to say that caution is unwarranted when introducing policies such as water fluoridation but the evidence is very strong that the recommended limits of fluoride in drinking water of 0.7–1.2 ppm are safe while offering really big public-health benefits.
Various allegations linking fluoride to cancer, thyroid and neurological problems lack convincing evidence. Another controversial claim linked maternal fluoride intake during pregnancy and slightly lower IQ scores in male children but the studies were poorly controlled and didn’t take maternal IQ and environmental pollution into account, as explained in HI Miller’s 2019 article in JAMA Paediatrics.
Ongoing evaluation of public-health policies in the light of scientific advances and social changes is, of course, very important. Although widespread use of fluoridated toothpaste and access to good dental care have reduced the relative importance of water fluoridation in affluent areas, it remains a critically important public-health measure in more deprived areas.
For the moment, universal water fluoridation remains an extremely valuable and effective public-health measure.
William Reville is an emeritus professor of biochemistry at UCC
