Back when I was a chemistry major, my professors told me in no uncertain terms that water fluoridation is a boon. It prevents millions of children from getting cavities. People who oppose it are hysterical know-nothings. We budding chemists absorbed both the specific and the general lesson. Fluoride is good. Scientists know best.

At just that time Rachel Carson was questioning scientific wisdom with regard to another issue: pesticides. I was taught that she was hysterical too. However as I read more widely and went beyond chemistry to ecology, I decided she was right. While I continued to respect science greatly, I came to see that some scientists can be hasty in judgment, narrow in understanding, out of date, or more loyal to their ideology or source of income than to the truth.

But I didn’t question fluoride. The consensus was strong. The dentists were behind it. Toothpaste makers hyped it. Half the nation’s cities fluoridate their water with no obvious ill effect. I classed fluoride opponents with UFO spotters and horoscope believers. Loonies.

I never looked at the evidence. I was thoroughly unscientific. So my sins finally caught up with me. People in towns on the verge of fluoridation kept asking me to write a column on the subject. I delayed. I made excuses. They sent me piles of information, which I didn’t read-until, out of curiosity, one day I did.

Then I went to Web. Then I started asking my scientific colleagues. The deeper I got into the topic, the more confused I got. Fluoridation is like capital punishment or gun control. Wildly polarized. Vested interests. Each side hoarding up selective evidence to prove itself right. Enough conflicting evidence to keep both sides happy. My head spun.

I did come out of the process more open-minded. Not all pro-fluoridation folks have done their homework. Not all anti-fluoridation folks are loonies-they include dentists and scientists and 1500 employees of the EPA. Both sides exaggerate a lot.

Here, for what they’re worth, are some conclusions I drew after my whirlwind immersion in this contentious topic.

* Fluoride does protect against cavities. Back in the 1940s, a dentist noted that people with “Texas teeth”-brown, mottled teeth that came from naturally high fluoride levels in their water-also had unusually low cavity rates. Comparisons of communities with varying natural fluoride levels led to the conclusion that about one part per million in drinking water was ideal to reduce tooth decay without triggering the mottling (which is called fluorosis).

* Tap water isn’t the only source of fluoride. That dosage of one part per million was calculated at a time when there was no fluoride in toothpaste. Nowadays we also get fluoride in soft drinks, in air pollution, in fruit juice, in children’s vitamin supplements. Studies over time seem to show that rising exposure to fluoride from other sources makes water fluoridation less protective of teeth and more likely to cause fluorosis.

* Fluoride is toxic. It doesn’t take much of it to kill vegetation, fish, mussels, crabs, shrimp, cattle. In human beings overexposure not only mottles teeth, it weakens bone. There are scientific papers linking fluoride to cancer and brain damage. The fluoride used by municipal water districts comes from phosphate fertilizer plants in Florida, where it is stripped from smokestacks to reduce air pollution. It contains not only fluoride, but heavy metals and other contaminants. If it were not put in drinking water, it would have to be treated as hazardous waste.

* There are arguments, even in the vaunted Journal of the American Dental Association, about how fluoride actually works. It may be by ingestion, getting itself implanted into tooth enamel. It may be by washing the mouth, inhibiting the growth of plaque bacteria. Fluoride in toothpaste may be just as effective as fluoride in drinking water.

* The epidemiological evidence doesn’t seem to be compelling either way. If you compare one fluoridated city (say, Toronto) with one unfluoridated one (Vancouver), you can pick your cities to get any result you want. Most of Europe does not use fluoride, much of America does. Is there more tooth decay there and more bone damage here? Expert panels have come down either way. That suggests that neither the positive nor the negative effects of fluoride (at low concentrations) can be very big.

Given the uncertainties, given the variation in intake from other sources, given the possibility of overdose, given known toxicity to other forms of life, if I lived in a city deciding about fluoridation, I would ask, isn’t there a better way to protect children’s teeth? Why fluoridate the whole water supply, the millions of gallons with which we flush toilets and take showers and water lawns, if our only target is children’s teeth? Why expose all people to a chemical of arguable benefit and some risk in a way they can’t control? Why dump that chemical into water supplies and then sewage plants and then waterways with almost no understanding of what happens to it after that?

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