Urinary fluoride and dental fluorosis in relation to kidney and liver function in adolescents and young adults in the United States.

backgroundHigher fluoride in plasma has been associated with lower eGFR among adolescents in the National Health and Nutrition Examination Survey (NHANES); however, whether fluoride exposure may contribute to decreased kidney function or fluoride may accumulate in plasma from lower kidney filtration could not be parsed. We examined the presence of dental fluorosis (DF; reflecting chronic fluoride exposure during tooth development) among adolescents and young adults and urinary fluoride (UF) levels among adolescents in relation to kidney and liver parameters in the United States (US).

methodsParticipants were 1,031 adolescents (aged 12–19 years) and 734 young adults (aged 20–29 years) from NHANES 2015–2016. DF was derived from Dean’s Fluorosis Index (DFI), and defined as any DFI score indicating very mild, mild, moderate, or severe fluorosis, while scores of normal and questionable were categorized as no fluorosis. Kidney or liver function parameters included estimated glomerular filtration rate (eGFR), serum uric acid, the urinary albumin to creatinine ratio, blood urea nitrogen (BUN), gamma glutamate transferase, aspartate aminotransferase, alkaline phosphatase, alanine aminotransferase, and albumin. We conducted survey-weighted linear regression adjusted for covariates to examine associations between fluoride exposure and kidney or liver function.

resultsAdolescent participants were 15 years old and adults were 24 years old on average. The median (IQR) UF concentration among adolescents was 0.48 (0.48) mg/L. Approximately 74% of adolescents and 70% of adults had DF with varying degrees of severity (ranging from very mild to severe). Each 1 mg/L increase in UF was associated with an approximately 5 mL/min/1.73 m² lower eGFR among adolescents (B = -4.73, 95% CI: -8.35, -1.12, p = 0.010). Higher UF was also associated with higher serum uric acid (mg/dl) (B = 0.17, 95% CI: 0.01, 0.33, p = 0.040) among adolescents. DF was associated with lower eGFR among adolescents (B = -3.72, 95% CI: -7.10, -0.33, p = 0.031) and adults (B = -3.90, 95% CI: -6.49, -1.31, p = 0.003). In addition, having DF was negatively associated with BUN among adolescents (B = -0.83, 95% CI: -1.44, -0.22, p = 0.007). No other significant associations were observed for liver markers.

conclusionChronic fluoride exposure during tooth development and recent fluoride exposure in adolescence are cross-sectionally associated with a lower rate of kidney filtration among adolescents and young adults in the US. Prospective US-based studies are needed to determine whether these associations are causal.