Association between fluoride exposure and kidney function in adults: A cross-sectional study based on endemic fluorosis area in China

Background: The kidney toxicity of fluoride exposure has been demonstrated in animal studies, and a few studies have reported kidney function injury in children with fluoride exposure. However, epidemiological information for the effects of long-term fluoride exposure on adult kidney function remains limited.

Methods: We conducted a cross-sectional investigation in Wenshui County, Shanxi Province to examine the association between fluoride exposure and kidney function in adults, and a total of 1070 adults were included in our study. Urinary fluoride concentrations were measured using the national standardized ion selective electrode method. And markers of kidney function injury (urinary NAG, serum RBP, serum Urea, serum C3, serum UA and serum αl-MG) were measured using automatic biochemical analyzer. Multivariate linear regression analysis and binary logistic regression model were used to assess the relationship between urinary fluoride and markers of kidney function injury.

Results: Urinary fluoride was positively correlated with urinary NAG and serum Urea, negatively correlated with serum C3. In multivariate linear regression models, every 1 mg/L increment of urinary fluoride was associated with 1.583 U/L increase in urinary NAG, 0.199 mmol/L increase in serum Urea, 0.037 g/L decrease in serum C3 after adjusting for potential confounding factors. In the binary logistic regression model, higher levels of urinary fluoride were associated with an increased risk of kidney function injury. Determination of kidney function based on urinary NAG, every 1 mg/L increment in the urinary fluoride concentrations was associated with significant increases of 22.8% in the risk of kidney function injury after adjusting for potential confounding factors. Sensitivity analysis for the association between urinary fluoride concentrations and markers of kidney function (urinary NAG, serum Urea, and serum C3) by adjusting for the covariates, it is consistent with the primary analysis.

Conclusions: Our study suggests that long-term fluoride exposure is associated with kidney function in adults, and urinary NAG is a sensitive and robust marker of kidney dysfunction caused by fluoride exposure, which could be considered for the identification of early kidney injury in endemic fluorosis areas.