Fluoridating water, or a funny thing happened on my way to backseat driving

I originally labelled this blog Backseat Driving back in 2004 because I anticipated it to be a blog where I would second-guess decisions made by politicians and other people. That worked out fine more or less until November 2010, when for some reason I was elected to the Santa Clara Valley Water District Board. Turns out that San Jose is the largest city in the US without fluoridated water supplies (in much of the city, anyway), and the seven of us directors have to decide whether we'll help or hinder the fluoridation process. So I'm pushed into the front seat for this one.

We've got some legal and economic issues to handle (it's not quite as cheap as everyone says, I want to know where the money's going to come from), but the relevant issue here is science. I read the guest post at climate blogger Coby Beck's place, The Case Against Fluoride, fairly closely a while back, especially the raucous debate in the comments. As a spectator with some, limited reading of the available information, I'd say the fluoridators seemed more persuasive than skeptics, but it wasn't the absolute demolishing that I expected.

The fluoride skeptics really hurt their cause when say fluoride doesn't prevent cavities - it's so obviously effective that people making this claim are damaging their own credibility. I'd consider it comparable to denying that the planet has warmed in the last 50 years.

The closer issue is adverse effects, and whether a substantial number of people are very slightly harmed by fluoridation, or if a small number of people are substantially harmed. The 2006 National of Sciences report doesn't condemn fluoridation, but it doesn't absolve it, either:

Bone Fractures

....Overall, there was consensus among the committee that there is scientific evidence that under certain conditions fluoride can weaken bone and increase the risk of fractures. The majority of the committee concluded that lifetime exposure to fluoride at drinking-water concentrations of 4 mg/L or higher is likely to increase fracture rates in the population, compared with exposure to 1 mg/L, particularly in some demographic subgroups that are prone to accumulate fluoride into their bones (e.g., people with renal disease)....There were few studies to assess fracture risk in populations exposed to fluoride at 2 mg/L in drinking water. The best available study, from Finland, suggested an increased rate of hip fracture in populations exposed to fluoride at concentrations above 1.5 mg/L. However, this study alone is not sufficient to judge fracture risk for people exposed to fluoride at 2 mg/L. Thus, no conclusions could be drawn about fracture risk or safety at 2 mg/L....

(In California, 2 mg/L was the limit, and 0.7 is the new proposed goal. -Ed)

Neurotoxicity and Neurobehavioral Effects

Animal and human studies of fluoride have been published reporting adverse cognitive and behavioral effects. A few epidemiologic studies of Chinese populations have reported IQ deficits in children exposed to fluoride at 2.5 to 4 mg/L in drinking water. Although the studies lacked sufficient detail for the committee to fully assess their quality and relevance to U.S. populations, the consistency of the results appears significant enough to warrant additional research on the effects of fluoride on intelligence....

Endocrine Effects

The chief endocrine effects of fluoride exposures in experimental animals and in humans include decreased thyroid function, increased calcitonin activity, increased parathyroid hormone activity, secondary hyperparathyroidism, impaired glucose tolerance, and possible effects on timing of sexual maturity. Some of these effects are associated with fluoride intake that is achievable at fluoride concentrations in drinking water of 4 mg/L or less, especially for young children or for individuals with high water intake. Many of the effects could be considered subclinical effects, meaning that they are not adverse health effects. However, recent work on borderline hormonal imbalances and endocrine-disrupting chemicals indicated that adverse health effects, or increased risks for developing adverse effects, might be associated with seemingly mild imbalances or perturbations in hormone concentrations. Further research is needed to explore these possibilities....

Genotoxicity and Carcinogenicity

....Whether fluoride might be associated with bone cancer has been a subject of debate. Bone is the most plausible site for cancer associated with fluoride because of its deposition into bone and its mitogenic effects on bone cells in culture....Several epidemiologic investigations of the relation between fluoride and cancer have been performed since the 1993 evaluation, including both individual-based and ecologic studies. Several studies had significant methodological limitations that made it difficult to draw conclusions. Overall, the results are mixed, with some studies reporting a positive association and others no association.

On the basis of the committee’s collective consideration of data from humans, genotoxicity assays, and studies of mechanisms of action in cell systems (e.g., bone cells in vitro), the evidence on the potential of fluoride to initiate or promote cancers, particularly of the bone, is tentative and mixed. Assessing whether fluoride constitutes a risk factor for osteosarcoma is complicated by the rarity of the disease and the difficulty of characterizing biologic dose because of the ubiquity of population exposure to fluoride and the difficulty of acquiring bone samples in nonaffected individuals.

These were the most troubling findings, mostly about what hasn't been proven, and mostly dealing with levels that are five times what's planned for drinking water. The report expressly ignored the benefits of fluoridation. It's important to balance out potential concerns over rare, severe complications related to fluoride with the certainty that rare, severe complications can result from cavities.

The bottom line as a policy maker in my little arena is that I shouldn't try and figure out the science myself, but I should try to figure out what the scientific consensus is, figure out where the consensus doesn't yet exist, and then plug that information into everything else we have to balance.

The science seems to favor fluoridation, but it's not a slam dunk. And we still have potential policy barriers, and the overall cost issues. Figuring this all out will be interesting.

UPDATE: I'll give the anti-fluoridators credit for quickly finding their way here. Personally, I'm not going to attempt to judge the quality of their sources. I don't care what any single paper or PhD says, I want to know what the consensus says.