Water fluoridation.(Brief Article)

Meta-analysis of fluoridation and fractures has been done

EDITOR--The article by McDonagh et al is valuable but not necessarily new in the area of fractures.[1] They conclude that the evidence relating fluoridation to fractures is weak and shows no significant effect either way. This is identical to the conclusion that we published in a 1999 meta-analysis not cited by McDonagh et al but listed on Medline.[2] This study located 26 studies in this area, compared with their 20, and reported a relative risk for fracture of 1.02 (95% confidence interval 0.96 to 1.09). Interestingly, sex, urbanicity index, and the quality (but not duration) of the study explained 25% of the variation between studies in meta-regression.

Further work in this area will need to be done at an individual level to advance this field, but even this is problematic given the paper by Phipps et al in the same issue of the journal, which reports on a very large cohort of women.[3] Nevertheless, it seems unlikely that water fluoridation to 1 ppm has any significant effect on the incidence of fractures at a population level based on the current (albeit weak) evidence.

Competing interests: None declared,

[1] McDonagh MS, Whiting PF, Wilson PM, Sutton AJ, Chestnutt I, Cooper J, et al. Systematic review of water fluoridation. BMJ 2000;321:855-9. (7 October.)

[2] Jones G, Riley, M, Couper D, Dwyer T Water fluoridation, bone mass and hip fracture: a quantitative overview of the literature. Aust N ZJ Public Health 1999;23:34-40.

[3] Phipps KR, Orwoll ES, Mason JD, Cauley JA. Community, water fluoridation, bone mineral density, and fractures: prospective study of effects in older women. BMJ 2000; 321:860-4. (7 October.)

 
Graeme Jones senior research fellow 
Menzies Centre for Population Health research, 
GPO Box 252-23, Hobart, Tasmania, Australia 
G.Jones@utas.edu.au 

Critical difference was overlooked

EDITOR--I wish to comment on the paper by McDonagh et al on fluoridation and the study by Phipps et al on bone fracture.[1 2] Although the paper by McDonagh et al deals a very serious blow to fluoridation on the basis of their findings of a much lower benefit for caries reduction than previously claimed and a much higher level of dental fluorosis than is acceptable, the authors do not make it clear that dental fluorosis is an indication of a toxic effect of fluoride, in a similar way that the blue line on gums is an indicator of lead poisoning. This raises the question of what other enzymes and proteins might be poisoned. The paper by McDonagh et al is only a partial scientific analysis. They did not consider work on the pineal or thyroid gland or many animal experiments showing an effect of fluoride on the brain.

On the basis of their meta-analysis, McDonagh et al claim that there is no evidence of a relation between hip fracture in elderly people and fluoridation but mischaracterise some of the key studies. For example, they indicated that Li et al showed no association.[3] Li et al showed, however, that at above 1.5 ppm hip fracture rates were doubled and above 4 ppm they were tripled. Although I pointed this out to McDonagh et al twice, they still report no association.

The most disturbing aspect of the study by Phipps et al is how much attention is given to the decrease in hip fracture incidence and how little to the increase in wrist fracture. The ostensible reason for this is that the 32% increase in wrist fracture is deemed insignificant. However, the supposed insignificance is based upon the fact that the 95% confidence interval is given as 1.00 to 1.71. Had the interval been 1.01 to 1.71, the increase would have been deemed significant. Bearing in mind that this result is achieved after many adjustments, the claim that long term exposure to fluoridated drinking water does not increase the risk of fracture is cavalier. It is also intriguing that McDonagh et al reported the …