Plain language summary
Fluoride is added to the water supply in some parts of the UK, US and Canada to help prevent tooth decay, but there is some concern that long-term exposure to fluoride could be harmful to health. Animal studies have indicated that fluoride may cause kidney and liver damage. This US study aimed to evaluate whether greater fluoride exposure is associated with altered kidney and liver function in adolescents. This cross-sectional study looked at data collected from the National Health and Nutrition Examination Survey (2013-2016). The average age of adolescents was 15 years. Fluoride levels were measured in blood and in household tap water. Higher levels of fluoride in the blood were associated with a lower estimated glomerular filtration rate, a higher blood uric acid concentration, and a lower blood urea nitrogen concentration. Higher levels of fluoride in tap water were associated with a lower blood urea nitrogen concentration. The researchers concluded that fluoride exposure may contribute to complex changes in kidney and liver function in US adolescents. However, researchers could not rule out the possibility that an altered kidney or liver function may impact the body’s ability to absorb or metabolise fluoride.
Abstract
BACKGROUND Hepato- and nephrotoxicity of fluoride have been demonstrated in animals, but few studies have examined potential effects in humans. This population-based study examines the relationship between chronic low-level fluoride exposure and kidney and liver function among United States (U.S.) adolescents. This study aimed to evaluate whether greater fluoride exposure is associated with altered kidney and liver parameters among U.S. youth. METHODS This cross-sectional study utilized data from the National Health and Nutrition Examination Survey (2013-2016). We analyzed data from 1983 and 1742 adolescents who had plasma and water fluoride measures respectively and did not have kidney disease. Fluoride was measured in plasma and household tap water. Kidney parameters included estimated glomerular filtration rate (calculated by the original Schwartz formula), serum uric acid, and the urinary albumin to creatinine ratio. Liver parameters were assessed in serum and included alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, blood urea nitrogen, gamma-glutamyl transferase, and albumin. Survey-weighted linear regression examined relationships between fluoride exposure and kidney and liver parameters after covariate adjustment. A Holm-Bonferroni correction accounted for multiple comparisons. RESULTS The average age of adolescents was 15.4 years. Median water and plasma fluoride concentrations were 0.48 mg/L and 0.33 μmol/L respectively. A 1 μmol/L increase in plasma fluoride was associated with a 10.36 mL/min/1.73 m2 lower estimated glomerular filtration rate (95% CI: -17.50, -3.22; p = 0.05), a 0.29 mg/dL higher serum uric acid concentration (95% CI: 0.09, 0.50; p = 0.05), and a 1.29 mg/dL lower blood urea nitrogen concentration (95%CI: -1.87, -0.70; p < 0.001). A 1 mg/L increase in water fluoride was associated with a 0.93 mg/dL lower blood urea nitrogen concentration (95% CI: -1.44, -0.42; p = 0.007). CONCLUSIONS Fluoride exposure may contribute to complex changes in kidney and liver related parameters among U.S. adolescents. As the study is cross-sectional, reverse causality cannot be ruled out; therefore, altered kidney and/or liver function may impact bodily fluoride absorption and metabolic processes.
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