Effects of fluoridation of community water supplies for people with chronic kidney disease

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Research on the effects of fluorides on oral healthhas been in existence for almost a century. Followingthe observation that communities with naturallyfluoridated drinking water had a lower incidence oftooth decay, many developed countries initiatedartificial water fluoridation programmes, wherebyfluoride is added to the reticulated water supply,such that it reaches approximately one part fluorideper million parts water (ppm) or 1mg fluoride per litreof water (mg/l). Recent reviews [1–5] summarizing theextensive fluoride literature have concluded that waterfluoridation reduces the prevalence of dental decay,and it is estimated that a median of six people need toreceive fluoridated water for one extra person to becaries-free [2]. Compared with other methods ofsystemic fluoridation (including fluoridated sugar,milk or salt, fluoride toothpastes, fluoride supple-ments), water fluoridation is argued to be the mostcost-effective, equitable and safe means to providecommunity-wide protection against tooth decay [6].As a result, artificial fluoridation of community watersupplies is currently supported by numerous interna-tional health and dental organizations, including theWorld Health Organization and the InternationalAssociation for Dental Research.However, while access to fluoridated drinkingwater has positive effects on dental health, thecharacteristics of fluoride metabolism mean thatfluoride consumption may have implications for thekidney. The calcified tissues in the human body contain99% of the body burden of fluoride and most of thisis non-exchangeable. Absorption of fluoride is rapidand extensive, with about 50% of the absorbedfluoride becoming associated with calcified tissueswithin 24h and the remainder being excreted in theurine. In infants and young children, the amount offluoride retained in calcified tissues is >50% of theingested daily amount. The renal clearance of fluorideis high, around 30–40ml/min in healthy adults [7].Fluoride is freely filtered by the glomerulus and thenundergoes a variable amount of tubular reabsorption.Fluoride excretion falls markedly in the presence ofan acid urine and is increased with higher rates ofurine flow [8–10]. Considering the pivotal role of thekidney in the body’s ability to metabolize fluoride,there have been surprisingly few attempts to synthesizestudies relating to the relationship between fluorideconsumption and kidney function. The most recentliterature reviews on the health effects of fluorideintake have contained limited discussion on thepotential impact on the kidneys [1–5].Recently there has been a resurgence of interest inthe artificial fluoridation of drinking water inAustralia, with efforts to expand the fluoridation ofpublic water supplies to the one remaining unfluori-dated capital city (Brisbane) and several unfluoridatedregional areas. With the renewed debate in Australiaregarding water fluoridation, questions have beenraised concerning the impact of fluoride consumptionfor the large proportion of the Australian populationaffected by chronic kidney disease (CKD). In thegeneral Australian community over age 25, there isevidence of at least one indicator of CKD (proteinuriaor reduced kidney function) in 16% of individuals[11]. However, CKD is frequently asymptomatic,and many afflicted individuals will have significantreduction of kidney function but no overt signs orsymptoms, and hence will be unaware they have thecondition.The United States National Kidney Foundationpublished a brief position statement on fluoridationof drinking water in the early 1980s [12], and concludedthat there was insufficient evidence to recommendthe use of fluoride-free drinking water for all peoplewith CKD. This position statement was reaffirmed in1998, but no new research or discussion was added.