Fluoride biomarkers and dental fluorosis in endemic Chinese children: a comparison of urinary and hair measures

This study aimed to assess fluoride exposure among school-aged children in endemic fluorosis areas of Jiangsu Province and to examine the relationships between urinary fluoride (UF), hair fluoride (HF), and dental fluorosis. In total, 320 children (aged 8–12) from two affected counties were included and divided into dental fluorosis (n = 140) and non-fluorosis (n = 180) groups. Spot urine and hair samples were collected. Dental fluorosis was diagnosed according to national standards (WS/T 208–2011). UF and HF were determined using standard methods (WS/T 89–2015; DZ/T 0253.4–2014). Generalized linear and logistic regression models were used for analysis. Median UF levels were 1.41 mg/L in the fluorosis group and 1.02 mg/L in the non-fluorosis group; median HF levels were 11.9 mg/kg and 11.5 mg/kg, respectively. HF was positively correlated with UF in both groups (non-fluorosis: β = 0.70, 95% CI: 0.17–1.23; fluorosis: β = 1.63, 95% CI: 0.69–2.56). Elevated UF (OR = 1.80, 95% CI: 1.35–2.40) and HF (OR = 1.27, 95% CI: 1.01–1.50) were significantly associated with higher odds of dental fluorosis. These findings indicate that both UF and HF are moderately predictive and limited discriminatory power biomarkers of internal fluoride exposure and are positively associated with dental fluorosis in children from endemic areas.