Fluoride and Kidney–Liver Function

A study recently published in Environment International suggested that fluoride exposure may increase the risk of kidney and liver damage.¹ The authors assert that this is an uninvestigated area that requires further exploration on the “relationship between low-level fluoride exposure and kidney-related parameters among United States adolescents.”¹ However, the only significance of this study we agreed upon was their mention of what could possibly happen with extremely elevated levels of fluoride in natural water sources. The authors pointed out other supportive studies occurring in both India and China; however, in these countries, natural levels of fluoride exist in the 3.5 ppm to 11.5 ppm ranges, and are found in the water, food, and air due to widespread burning of coal. With the current optimal level of water fluoridation at 0.7 ppm (recommended by the US Centers for Disease Control and Prevention (CDC) and the Environmental Protection Agency) and recommendations of no more than 2 ppm to prevent severe enamel fluorosis and 4 ppm as a safety limitation to limit skeletal fluorosis, the risk purported by the authors seems unfounded.^2,3

US water systems adhere to the lower limit of 2.0 ppm whether it is natural or supplemented to ensure safety and reduce the incidence of fluorosis.⁴ With modern testing equipment, municipal water systems can closely monitor the amount of the fluoride mineral being added to the water supply to ensure safety.

STUDY LIMITATIONS

The authors’ study design—single cross-sectional—provides data analysis of variables collected at one given point of time (year 1983) across a sample population (1,742 adolescents who had plasma and water fluoridation measures respectively and did not have kidney disease).¹ This study design only measured prevalence during this time. The authors did not explore the incidence or the number of new cases that developed, or how these new cases developed after this time period.

The study stated that “for analyses of water fluoride, 1,942 participants had water fluoride levels and we excluded an additional 200 participants who reported that they did not drink tap water, resulting in a sample size of 1,742,” but the authors did not state what the specific fluoride level (ppm) was.¹ The investigation analyzed data from 1983 exclusively. In 1983 and up until 2015 when the recommendations were updated, the guidelines for water fluoridation and ppm were based on climate: 0.7 ppm for warmer climates and 1.2 ppm for colder climates.⁵ Depending on the climate where participants lived, overall fluoride levels could have been higher (up to 1.2 ppm), but the specific geographic locations of participants were not included in the materials and methods section.¹

Another way of receiving fluoride, the “halo effect,” was not accounted for by the authors. For example, orange juice made in Florida with fluoridated tap water is shipped to other areas of the country and then ingested by consumers. Also, blood collection times were not standardized in the study. This could have led to altered half-life readings for fluoride. Next, the authors did not control for the following variables: medication usage, drug/alcohol use, lead/arsenic exposure, sugar/carbohydrate consumption, and physical activity. Although two people were removed from the study for having estimated glomerular filtration rate (eGFR) of under 60, the National Kidney Foundation currently recommends that individuals with an eGFR from 60 to 89 be monitored for kidney issues.⁶ As 39.9% of the study participants were overweight or obese, closer monitoring and analysis would have been advisable. Diets high in sugar and carbohydrates can also negatively impact both the kidneys and liver.

Finally, the specific ion analysis testing method used in this study has many sources of error. The researchers conducting the testing can introduce contamination by not using clean collection methods, or by failure to calibrate the equipment. Instrument “drift” was also a common failure of the electronic device in this basic, low-level type of testing. Since the 1980s, more accurate testing has been introduced in scientific studies. Specific ion testing is still used by water systems, but it is reserved for general testing of fluoride levels.

BENEFITS VS RISKS

The benefit of fluoride in public water systems in caries reduction outweighs any potential adverse effects like mild enamel fluorosis. Community water fluoridation is one of the most cost effective and equitable ways to prevent tooth decay, period. The CDC named fluoridation as one of the top 10 most significant public health measures of the 20th century.⁷

Clinicians can educate patients on the importance of fluoride by keeping up-to-date on what the current evidence states on this topic. Ernest Newbrun, DMD, PhD, explained it best in his evidence-based publication, which concluded that “maximal caries‐preventive effects of water fluoridation are achieved by exposure to optimal fluoride levels both pre‐ and post-eruptively.”⁸ Dental providers should be proactive in learning both sides of the story—those for water fluoridation and those opposed to it—in order to properly advise patients and the public on this topic. Clinicians need to be aware of the misinformation about water fluoridation that is currently surfacing on the Internet and focus more on what the evidence-based research demonstrates to appropriately educate concerned patients.

REFERENCES

1. Malin AJ, Lesseur C, Busgang SA, Curtin P, Wright RO, Sanders AP. Fluoride exposure and kidney and liver function among adolescents in the United States: NHANES, 2013-2016. Environ Int. 2019;132:105012.
2. United States Department of Health and Human Services. US Public Health Service Recommendation for Fluoride Concentration in Drinking Water for the Prevention of Caries. Available at: cdc.gov/​fluoridation/​index.htm. Accessed September 24, 2019.
3. US Environmental Protection Agency. Questions and Answers on Fluoride. Available at: epa.gov/​sites/​production/​files/​2015-10/​documents/​2011_​fluoride_​questionsanswers.pdf. Accessed September 24, 2019.
4. Yeung CA. A systemic review of the efficacy and safety of fluoridation. Evid Based Dent. 2008;9:39-43.
5. US Centers for Disease Control and Prevention. Engineering and Administrative Recommendations for Water Fluoridation. Available at: cdc.gov/​mmwr/​PDF/​rr/​rr4413.pdf. Accessed September 24, 2019.
6. National Kidney Foundation. Estimated Glomerular Filtration Rate (eGFR). Available at: kidney.org. Accessed September 24, 2019.
7. Recommendations for using fluoride to prevent and control dental caries in the United States. Centers for Disease Control and Prevention. MMWR Recomm Rep. 2001;50(RR–14):1–42.
8. Newbrun E. Systemic benefits of fluoride and fluoridation. J Public Health Dent. 2007;64 (Suppl S1):35–39.

From Dimensions of Dental Hygiene. October 2019;17(9):10,13.