This week the secretary for health, Alan Johnson, introduced a smart-aleck idea: Local authorities adding fluoride to the water supply. Immediately all hell broke loose, and the split of opinion for and against the idea crept inexorably out of the woodwork and into the papers.

Although all health authorities in England have the power to require water companies to add fluoride to the water, currently only a handful do. The government’s reasoning is that the supplementation of water with fluoride will reduce the number of dental cavities in the general population, and therefore the bill presented to the NHS by incalculably well-paid dentists will decrease.

At first glance, this all seems very sensible. But a large number of people appear convinced that it’d be better to chew deadly nightshade while rolling around naked in a bunker lined with cancer-impregnated scouring-pads.

All this prompted an article in the British Medical Journal. This found, when thousands of studies are taken into account, a marginal positive effect on tooth decay - amounting to around 15% fewer cases. Also, when they looked into the risk of complications such as hip fractures, they found little to be concerned about. However, they also found that the incidence of weird white-spotty teeth is almost half the population in some high fluoride areas. Severe weird and really-really-white-spotty teeth can happen in 1 in 8 people. It also found that despite earlier studies ruling out the possibility of increased cancer and fractures, they really weren’t well enough designed to reliably spot them.

What really fascinates me here, though, is the bizarrely exaggerated reaction of the anti-fluoride brigade. A quick browse of the world-wide lunatic repository informs me that fluoride is more poisonous than lead, but slightly less poisonous than arsenic. Another site assures me confidently that fluoride does indeed contain an awful lot of “toxins”, and that it also contains an unusually strong “binding molecule” requiring you to to buy one of their special water-filters without delay or face the untimely death of your children, you monster.

These sorts of reactions from scare groups are fairly standard. On this issue, however, the government isn’t behaving much better. Alan Johnson has gone on record bandying about a 50% improvement figure, which isn’t based on any body of evidence I can find. I suspect he is quoting the results of a single study in isolation, which is simply the wrong way to go about this- you need to look at the entire literature. When this is done, the 50% figure looks foolish. The reality, frustratingly, is much harder to call.

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