Under the Microscope/Prof William Reville:Public mains drinking water in Ireland is artificially fluoridated as a public health measure aimed at preventing tooth decay. Studies have clearly shown that fluoridation is effective in this regard. However, some people are concerned that fluoride may also cause ill-health and they call for an end to our water fluoridation policy.
But extensive research into possible ill-health effects of fluoride at the levels used to fluoridate public water supplies have failed to find any ill-effects. The only negative effect reported is a mottling of the tooth enamel, called fluorosis that affects a small percentage of people. This is really a cosmetic effect. While it is understandable that most people would prefer to be able to exercise personal choice over whether to ingest any chemical, it seems that, in this case, the effects of universal water fluoridation are overwhelmingly positive. An overview of water fluoridation was published by J Mullen in British Dental Journal, Vol. 199, No. 7 (2005).
The correlation between fluoride in drinking water and healthy teeth was first noticed in America early in the 20th century. Epidemiological studies confirmed this and it was determined that an optimum effect was obtained at a fluoride concentration in water of one part per million (1ppm). Public water fluoridation schemes were introduced in America. Fluoridation of public water supplies in Ireland at a level of 1ppm was introduced in 1964 under Sean McEntee, then minister for health.
About 40 countries have water fluoridation schemes, but in some cases only a small proportion of the population is covered. Population coverage in a selection of countries include the US (64 per cent), Canada (43 per cent), Panama (18 per cent), Ireland (73 per cent), Australia (61 per cent), New Zealand (61 per cent), Israel (25 per cent), Malaysia (70 per cent), UK (10 per cent), Singapore (100 per cent), Brazil (41 per cent), Argentina (21 per cent), Chile (40 per cent), Spain (10 per cent), Columbia (80 per cent).
Early studies of effects of fluoridation showed a reduction of 50 per cent or more in tooth decay. Fluoridated toothpaste was introduced in the early 1970s and this has contributed to the general improvement in dental health in OECD countries in recent decades. Fluoridated water supplies still effect a 50 per cent improvement in dental health compared to non-fluoridated areas, but the absolute value of this 50 per cent improvement has decreased mainly because of fluoridated toothpaste. However, public health experts consider that sufficient beneficial effects of water fluoridation remain to justify its continuation.
There is no public water fluoridation in Northern Ireland. A recent study compared tooth decay rates on either side of the Irish border. Decay rates had been similar on both sides prior to the introduction of water fluoridation. The recent study found that decay rates in Northern Ireland are now about 50 per cent higher than in the Republic of Ireland, although fluoride toothpaste usage seems to be higher in Northern Ireland.
The only negative effect associated with water fluoridation is a cosmetic effect of enamel discolouration called fluorosis. The extent of fluorosis is measured on a six point scale - none, questionable, very mild, mild, moderate and severe. In Ireland, where 73 per cent of us are on fluoridated water, 80 per cent of the population has either no fluorosis or questionable fluorosis, and about 7 per cent have a level that might cause aesthetic concern, ie mild or higher.
The treatment of fluorosis is simple. Most discolouration is confined to the outer tenth of a millimetre of tooth enamel. This can be readily abraded away by the dentist.
The safety of water fluoridation has been intensively studied over the years. Perhaps the biggest study in recent times was the York Review of Public Water Fluoridation carried out by the UK NHS Centre for Reviews and Dissemination, University of York, 2000. This was followed by the Medical Research Council Review in 2004.
The York Review critically evaluated over 3,000 publications relevant to dental and general effects of water fluoridation on humans. It concluded that, apart from cosmetic dental fluorosis, there is no clear evidence for any adverse effects from water fluoridation. The MRC review reached similar conclusions. The Irish Forum on Fluoridation which reported to Micheál Martin, Minister for Health and Children, in 2002, agreed with the York Review.
There have been allegations that water fluoridation is linked to a host of diseases including cancer, Alzheimer's Disease, osteoporosis, and so on, but none of these allegations stand up to scrutiny. Nevertheless, such charges continue to be made.
To take these charges seriously is to champion the odd negative report over the very many studies, including several huge reviews of the literature, that find no evidence of a link between water fluoridation and ill-health.
Also, the World Health Organisation favours fluoridation of public water supplies.
The Irish Forum on Water Fluoridation 2002 said fluoridation of Irish mains water should continue, but fluoridation levels should be cut from 1ppm to 0.7ppm. It also said infant feeding formula should continue to be prepared using boiled mains water.
Fluoridation of mains water was introduced here before the era of the environmental lobby. There is no chance that fluoridation could be introduced today. There are, it seems to me, two reasons for this. First, it "goes against the psychological grain" to have no choice over being dosed with a "chemical". Second, and more significantly, protesters citing the odd allegation of ill-health effects of fluoridation would win the day because it is much easier to seed doubt and fear in people's minds than it is to seed reassurance.
On balance, we are fortunate that this public health measure, which benefits all and harms none, is already in place.
William Reville is associate professor of biochemistry and public awareness of science officer at UCC, understandingscience.ucc.ie