Fluoridation of drinking water and chronic kidney disease: absence of evidence is not evidence of absence

Extract

Sir,

Ludlow et al. [1] only confirmed that our knowledge of the potential adverse effects of chronic low fluoride supplementation of drinking water on normal or diseased kidneys is insufficient. More than 60 years after water fluoridation, there is no high-level evidence as most published studies are small, have methological deficiencies or are otherwise flawed.

There are two areas of concern regarding the nephrotoxic potential of fluoride. A small and inclusive amount of research suggests that fluoridation of community water actually causes kidney disease. Kidney damage to tubular function and structure, and reduction in glomerular filtration rate occurred in residents of endemic fluoride areas [2] and anecdotal cases of fluoride intoxication [3] suggested a causal relationship between fluoride intake and renal failure. Ludlow et al. are correct that no evidence of an increased frequency of kidney disease or tubular dysfunction has been observed in early US epidemiological studies, comparing non-fluoridated areas (0.3 mg/dl) to up to 8 mg/l fluoride in drinking water. None of these studies described renal function of the participants or serial changes in simple urinalysis. Of interest, the data of a recently published study suggested that drinking water contains fluoride levels over 2.0 mg/l—half of the fluoride concentration deemed safe by the US Environmental Protection Agency (EPA)—could cause damage to renal tubular structures in children. This conclusion is based on an investigation of 210 children living in areas of China with varying levels of fluoride in the community water (0.6–5.7 ppm). Children drinking water with more than 2 ppm fluoridewere found to have increased levels of NAG and yGT in their urine—both markers of renal tubular damage [4].