Experts: compelling public health case for fluoridation

Water fluoridation is back in the news today with reports that the Hutt City Council is to discuss water fluoridation at their meeting tonight (11 October 2011).

The issue has attracted much attention throughout the country with some councils re-evaluating their policies around fluoridation of water. Earlier this year, Ruapehu District Council decided to stop fluoridating its water supply to Taumarunui.

According to the Ministry of Health, currently 60% of New Zealanders are drinking fluoridated water, and the decision to fluoridate is down to each local council and local community.

But what does the scientific evidence say about the benefits of fluoridation and will there be any adverse effects on the health of the population of we cease to fluoridate the water supply?

The SMC asked experts for their views on the current scientific evidence on fluoride. Further comments will be added to the SMC website as they are received:

Michael Beasley, Medical Toxicologist, National Poisons Centre, University of Otago, comments:

“We are all exposed to fluoride; all drinking water supplies in NZ contain some fluoride. The practice of fluoridation involves increasing the amount of fluoride already present, rather than introducing it as something new. (The same approach has been used to good effect in the past; eg iodide in salt to help reduce the incidence of hypothyroidism (“goitre”) in NZ; it has also been proposed to add folate eg: in bread in an effort to reduce the risk of certain birth defects – adopted in Australia I think).

“As a medical toxicologist I am reminded constantly about the primacy of dose as a determinant of effect; even oxygen is toxic if you breathe too high concentrations for too long. The corollary is that something toxic at ‘high’ levels can be helpful (or even essential) at lower, more appropriate levels. The trick is to define the optimum dose, where benefit exceeds risk. I am struck by the fact that the vast majority of animal studies claiming some adverse effect(s) of fluoride are conducted at doses (or concentrations in drinking water) much higher than that occurring in humans living in areas of fluoridated water supplies. The findings (such as they are) are therefore not easily generalisable to the latter situation.

“The same applies to the Chinese IQ studies [which attempted to quantify cognitive capacities in children] (in terms of a measure of IQ) as a function of the fluoride concentrations in their drinking water. Not only has their overall design been criticised, but their relevance to the NZ scene is questionable. For example, they often involve comparing the IQ’s of children living in villages with (naturally occurring) “high” drinking water F levels with the IQs of those from areas with “low” levels. However the “high” levels are generally much higher than those occurring in NZ fluoridated water supplies (range 0.7 to 1.2 ppm, with increasing emphasis on 0.7 to 1.0 ppm). These NZ fluoridated levels are actually much closer to the levels found in the “low fluoride villages” in China, whose children are used as the control group in the IQ studies (as opposed to the high fluoride study group).

“I am as yet less familiar with some of the other issues; one of which is a claimed increased risk of osteosarcoma in young males. However this seems to be based on the result of just one study. However earlier today I happened to note a recent study from Ireland, which does not support this claim.

“The NFIS continues to scan the literature, and intends to assess it in an objective fashion.”

Dr Robin Whyman, Senior Dentist and Specialist in Public Health Dentistry, Community Dental Service, Hutt Valley District Health Board, comments:

“Fluoridation of water supplies is an effective way of reducing our risk of developing dental decay. It has its greatest effect for people who have the highest risks of dental decay, and therefore acts to reduce inequalities in oral health that are present across our population. However, it helps everyone with their own natural teeth. With an aging population retaining more of their own natural teeth it remains an important part of our approach to reducing the effects of dental decay in New Zealand communities.

“New Zealand and overseas research continues to show that water fluoridation reduces the risk of tooth decay in both children and adults.

“There is a responsibility to monitor water fluoridation programmes to ensure that the benefits are being achieved and that adverse side effects are not occurring. That work is happening, through the Ministry of Health and district health boards and through international advisory panel reviews.

“Inevitably a range of results occur when many studies are undertaken, but the balance of that evidence continues to show that water fluoridation at levels appropriate to prevent tooth decay (0.7 – 1ppm) is safe and remains effective at reducing tooth decay.”

Professor Murray Thomson, Professor of Dental Epidemiology and Public Health, The University of Otago comments:

“There is a compelling public health case for community water fluoridation. Children and adults have better teeth because of it, and the oral disease burden from not having community water fluoridation is more extensive than many people realise. Some people have asked whether community water fluoridation is no longer effective. National data on 5-year-olds and 12-year-olds show clearly that ethnic inequalities in oral health are much greater among children in areas without community water fluoridation. It’s not just children, either.

“The most recent national oral health survey (conducted in 2009) showed that the average adult living in an area without fluoridated water had more than 3 more decayed, missing or filled teeth than one living in an area with community water fluoridation. In 2008, an international systematic review of studies on adults found that tooth decay experience was lower by 27% among adults living in fluoridated communities. This is an important difference.

“In line with the rest of the Western world, New Zealand’s population is ‘greying’; people are living longer, and women are having fewer babies (and later). Along with this increase in the numbers of older people, more and more of them are keeping their own teeth. In 1976, for example, 72% of those aged 65 to 74 years had no natural teeth; by 1988, this had fallen to 59%, and it was down to 30% by 2009 (and is projected to be about 14% by 2031).

“Recent dental studies where older people have been followed over time show that their tooth decay rate is at least as high as that of adolescents, and considerably higher if ongoing tooth loss is taken into account. Furthermore, it has been shown to be twice as high again for people living in rest homes, and more than twice as high again among those with dementia. In general, very little in the way of organised dental preventive care goes on in rest homes, and therefore any advantage that can be conferred through water fluoridation is to be welcomed.”