DEPENDING on who you listen to, fluoride is either a poison or a tried-and-tested cure for an entirely preventable disease. In Southampton, health chiefs want to add it to the water supply of two-thirds of the city’s residents in a bid to improve chronic dental health, particularly in more deprived areas.

They say the increasingly common sight of children as young as three with mouths full of blackened, missing or replaced teeth is proof enough that something must be done.

But the plans have met with an angry and vocal response in some quarters.

Anti-fluoride campaigners argue that not only is it immoral to mass-medicate without the explicit consent of every individual, but that doing so could put people at risk from all manner of other medical side-effects.

“It is a poison – that’s its only status in UK law,” is the blunt assessment of Peter Richards, of Hampshire Against Fluoridation.

“It comes out somewhere between lead and arsenic for toxicity. It’s hugely dangerous stuff.”

With talk of bone cancer, lowered IQ in children, mottled teeth, thyroid problems, brittle bones leading to painful fractures and effects on reproductive systems causing birth defects, it is no surprise the question of fluoridation evokes strong emotions.

Fluoride is already naturally present in our water – in Southampton it is found at a level of around 0.08 parts per million (ppm).

Health chiefs want that to be topped up to 1ppm.

So how safe is fluoridation? What’s the evidence and how reliable is it?

The first and perhaps most surprising observation is that only a small amount of high-quality research on the effects has been completed. And vast swathes of that is inconclusive.

Take the Government-commissioned study in 2000 which looked at the evidence in favour of artificially increasing levels of fluoridation, while also aiming to review proof of any negative effects the process might have.

This study, published by the University of York, bemoaned the quality of the previous research, saying much of it had not been carried out to modern standards, or simply lacked objectivity.

It concluded that fluoridation is likely to have a beneficial effect on the health of children’s teeth – but added its impact is not guaranteed.

Similarly, the authors said that on average six people need to be fluoridated for an extra one to be decay-free – but then also revealed instances of a slight increase of problems in areas with topped-up fluoride.

The York Review concluded that the available evidence shows the benefits of fluoridation “come at the expense of an increase of fluorosis” – discoloured teeth.

It also studied other adverse effects, and while it said there was little proof of any links with cancers and bone fractures, it said the evidence available was so poor there could be no confident assertions drawn from it.

The authors called for more research – and recommended studies of the ethical, environmental, ecological, cost and legal implications too.

So does reassuring evidence lie across the Atlantic, where the fluoride crusade began in America?

Here the potential beneficial effects of fluoride in reducing tooth decay was spotted following the study of a group of children living in the Pikes Peak region of Colorado in 1909.

It transpired they lived in an area with naturally excessive fluoride in the water, and this could be linked to their pitted and discoloured teeth – a condition now called fluorosis and one of the proven drawbacks of higher levels of fluoride.

Crucially, however, their teeth displayed a much lower rate of decay than had been seen elsewhere, suggesting controlled fluoride could be an excellent preventative measure.

This study convinced medical pioneers across America to look at whether they could improve dental health by managing levels of fluoride in water and eventually led to comparison exercises between paired cities.

As part of the earliest of these experiments, in January 1945, Grand Rapids in Michigan became the first place to add fluoride to its water supply for the aim of dental benefit.

Concerns have been voiced in America ever since but the fluoridation practice has nonetheless spread across the United States and beyond, and today it is used in many countries in both the developed and developing worlds.

In the US, nearly two-thirds of the population receives topped-up levels in its water supply, with a target of three-quarters by 2010 – a level already experienced in the Irish Republic.

Australia, Chile, Brazil, Canada all have large-scale fluoridation too, while around ten per cent of people in Spain and Britain are currently fluoridated.

The practice was introduced to parts of the UK in the 1960s, most notably in the West Midlands and north-east.

Southampton health chiefs point to the experiences there – where, on average, children have half the number of decayed teeth – as their main argument for fluoridating.

Yet Europe has been divided.

Austria, Belgium, Denmark and Holland have rejected the fluoridation route, while others started but have since stopped.

West Germany, Sweden, Holland and Japan all abandoned fluoridation in the 1970s, two decades after its introduction, while the Soviet Union, Czechoslovakia, East Germany and Finland had all followed suit by the mid-1990s.

This then is the complex, conflicting and confusing backdrop against which the fluoride battle is being fought. And each faction naturally picks at the tit-bits of research which bolster their arguments.

Elizabeth McDonagh, chairman of the National Pure Water Association, opposes fluoridation.

She said: “Dental fluorosis apart, there is considerable evidence of harm from fluoride at low levels and cumulatively. Thalidomide was touted as safe and effective’ before its damaging effects became known, and the dangers of smoking and asbestos went unrecognised for years.

“Fluoride is a very subtle poison, affecting enzymes, hormones and genetic structures besides teeth and bones. The York Review said that before fluoridation could be implemented as safe, further high-quality research was needed. No further high-quality research in this area has been done.”

But our health chiefs remain convinced of the benefits.

Professor Cyrus Cooper is director of the Medical Research Council Epidemiology Resource Centre at the University of Southampton, which studies the factors affecting the health and illness of the population.

He backs fluoridation.

“Higher levels of fluorosis is absolutely a price worth paying,”

he said. “In some parts of the world you get fluorosis which affects the bones, but these are if there are huge doses of fluoride and that doesn’t apply to the levels we’re talking about.”

Professor Cooper, who has been involved in fluoridation research himself, maintains there is no increased risk of fractures in fluoridated areas, and also doubts suggestions of other health problems.

He said he does not believe there is evidence fluoridation causes cancer, nor that it affects reproductive systems, kidneys, or causes brain damage.

“Those claims are much wilder in my view. I don’t think there’s an evidence base to prove them at all.”

The professor believes fluoridation would benefit Southampton, although he can see why some are against it.

“Without doubt, I would fluoridate.

I can understand a person coming down on the other side of the line. I just wouldn’t agree with them.

“It is an ethical dilemma, and even with all the evidence not everyone would say yes. But I think everything is moving towards much more research and less problems, other than that of our right to choose.”

He believes even those with healthy teeth should support fluoridation because it would reduce social inequality.

“What they are promoting is the ability for everyone to share in the general wellbeing that they have been lucky enough to enjoy.”

While the professor and others on both sides have made up their minds, for many the jury is still out.

The problem for us as a community is that, while our children’s teeth are getting steadily worse, we have no idea when that jury will return.

And even when it does, will its verdict be unanimous?