Last updated: September 16, 2016
After drinking water or beverages, or eating food that contains fluoride, roughly half of the fluoride is absorbed and retained mainly in bones and teeth.1,2 The remaining fluoride is filtered out by the kidneys and cleared from the body in urine.1,2 Because of the role of the kidney in fluoride metabolism and excretion, it is important to assess whether adding fluoride to the water is safe for kidney health.2 In the United States, more than 10% of adults aged 20 years or older suffer from various stages of chronic kidney disease (CKD),3 making the question of kidney safety especially important.
No human epidemiological studies have observed increased rates of renal disease in populations exposed to drinking water with optimal fluoride concentrations for caries prevention.2,4 Studies carried out on people living in regions where there is endemic fluorosis, however, indicated that ingestion of fluoride at higher levels than optimal may increase the risk for some people to develop adverse renal effects.4-6 Because subjects of these studies might have been at greater risk for malnutrition and exposures to various environmental chemicals, it was recommended to carry out a similar study in North America in areas with high levels of natural fluoride in the drinking water.4 Evidence from laboratory and bioassay research implies that impairment of kidney function can result in changes to the way in which fluoride is metabolized and eliminated from the body resulting in an increased burden of fluoride.4,7,8 Thus there is a particular need of studies to determine the effect of high doses of fluoride on renal function and to determine the clinical significance in patients with renal impairment.
On the basis of available evidence, the National Kidney Foundation (NKF) made the following statements and recommendations in 2008:9
- Dietary advice for patients with CKD should primarily focus on established recommendations for sodium, calcium, phosphorus, energy/calorie, protein, fat, and carbohydrate intake. Fluoride intake is a secondary concern.
- Due to a lack of randomized trials specific to patients with CKD, the NKF does not have specific recommended levels of fluoride intake for persons with CKD and recommends further research. Furthermore, NKF acknowledges that monitoring total fluoride intake can be difficult due to a lack of labeling on foods and beverages.
- All dialysis treatment should follow standards set by the Association of the Advancement of Medicinal Instrumentation (AMMI). Failure to use the recommended water treatment processes like reverse osmosis or deionization and management protocol could result in fluoride intoxication, especially when operator errors could include the addition of excess fluoride to the public water system, or the use of exhausted ion exchange resins.
- The risk for persons with CKD from fluoride is likely greatest in areas with high levels of naturally occurring fluoride. Persons with CKD should be notified of the potential risk of fluoride exposure by providing information on the National Kidney Foundation website, including information from the NRC report and the Kidney Health Australia position paper.
Although research on the topic is limited, the evidence of the safety of fluoridation supports the continued use of water from fluoridated community water systems for people both with healthy kidneys and those with kidney disease, for drinking water purposes.
SELECTED SYSTEMATIC REVIEWS ON THIS TOPIC
NRC REPORT (2006)
The NRC committee examined three aspects of kidney functions with respect to fluoride’s toxicity; 1) whether or not there was a link between fluoride and kidney stones, 2) the mechanism of fluoride toxicity on renal tissue at high doses, and 3) what special considerations should be made for people with kidney failure who live in areas with naturally high levels of fluoride in the water. Based on an analysis of the published research, it was concluded that:
- Research on this topic, on humans and animals, has been sparse, and the direction of the influence of fluoride (promotion or prevention of kidney stones) has been mixed. No published studies were found which suggested that consuming fluoride at 1 mg/L, the level previously found in community water fluoridation (currently 0.7 mg/L in the US), could affect the kidney. Research carried out in India on over 18,000 people who lived where the fluoride concentration in drinking water ranged from 3.5 to 4.9 mg/L showed a greater likelihood for the development of kidney stones by those who had signs and symptoms of skeletal fluorosis. Kidney stone formation, however, could have been due to malnutrition in this population, and the committee members concluded that such research should be carried out in the US, in areas where the drinking water was 4 mg/L in fluoride concentration.
- The results of animal studies helped to determine how the kidney responded to high doses of fluoride. ATP-dependent calcium uptake in rat kidneys, the ATP-ase pump in cultured rabbit ascending loop cells, and kidney phospholipids all were significantly affected by high doses of fluoride.
- People with impaired renal function, or currently on dialysis due to renal failure, tended to accumulate fluoride in bone much more quickly than normal. What was not clear was whether bone changes in renal osteodystrophy could be attributed to excess bone fluoride accumulation alone, or whether it could have been due to combination with other elements such as magnesium and aluminum. For all patients undergoing dialysis the water used for dialysis should meet the required guidelines for water quality published by their equipment manufacturer.
LUDLOW M ET AL. (2007)
The authors conducted a narrative review of the literature published before July 2006 to answer the following question and inform the Kidney Health Australia on the use of fluoridated water: 1) whether consumption of fluoridated drinking water increases the risk of developing chronic kidney disease (CKD), 2) if there are negative health effects for people with kidney disease who consume fluoridated drinking water, 3) if there are particular risks for people using fluoridated water for dialysis. Based on the poor evidence quality and deficient methodological rigor of the identified studies, the authors suggested no definitive conclusions regarding the association between consumption of optimally fluoridated community water and CKD.
KIDNEY HEALTH AUSTRALIA HAS DEVELOPED THE FOLLOWING POSITION STATEMENTS (2007) ON THE BASIS OF THE AVAILABLE EVIDENCE:
- There is no evidence that consumption of optimally fluoridated drinking water increases the risk of developing CKD or poses any health risks for people with CKD, while there is consistent evidence that impairment of kidney function results in changes to the way in which fluoride is metabolized and eliminated from the body, resulting in an increased burden of fluoride.
- There is limited evidence that people with stage 4 or 5 CKD who ingest substances with a high concentration of fluoride may be at risk of fluorosis. Monitoring of fluoride intake and avoidance of fluoride-rich substances would be prudent for people with stage 4 or 5 CKD.
- Fluoride concentrations in the final feed water to the dialysis machine must comply with established water quality guidelines.
In 2011, Kidney Health Australia responded to call to update their position published in 2007 and conducted updated literature review for the databases available by May 2011 and came to the same conclusions.
- Whitford GM. The physiological and toxicological characteristics of fluoride. J Dent Res. 1990;69(Spec. Issue):539-49,556-7
- National Research Council. Health effects of ingested fluoride. Washington, DC. The National Academies Press. 1993.
- Centers for Disease Control and Prevention. Prevalence of CKD Stages, 1988-1994 vs. 1999-2006 vs. 2007-2014. Available at https://nccd.cdc.gov/ckd/detail.aspx?QNum=Q8
- National Research Council. Fluoride in Drinking Water: A Scientific Review of EPA’s Standards. Washington, DC. The National Academies Press. 2006.
- Singh PP, Barjatiya MK, Dhing S et al. Evidence suggesting that high intake of fluoride provokes nephrolithiasis in tribal populations. Urol Res. 2001;29(4):238-44
- Chandrajith R, Dissanayake CB, Ariyarathna T et al. Dose-dependent Na and Ca in fluoride-rich drinking water- Another major cause of chronic renal failure in tropical arid regions. Sci Total Environ. 2011;409(4):671-5
- Ludlow M, Luxton G, Mathew T. Effects of fluoridation of community waster supplies for people with chronic kidney disease. Nephrol Dial Transplant. 2007;22(10):2763-7
- Kidney Health Australia. 2011 Review of Kidney Health Australia Fluoride Position Statement. Available at http://kidney.org.au/cms_uploads/docs/2011-review-of-fluoride-position-statement.pdf
- National Kidney Foundation. Fluoride Intake in Chronic Kidney Disease. April 15, 2008. Available at https://www.kidney.org/sites/default/files/docs/fluoride_intake_in_ckd.pdf