Relatively low fluoride in drinking water increases risk of knee osteoarthritis (KOA): a population-based cross-sectional study in China

Previous studies indicate that fluoride in drinking water has a toxic effect on cartilage and skeleton, which triggers osteoarthritis (OA) of which the most frequent is knee OA (KOA). A cross-sectional study was conducted to assess the association between fluoride exposure and KOA among 1128 subjects. Water fluoride (WF) and urinary fluoride (UF) were chosen as external exposure (internal exposure) of fluoride. Logistic regression analysis showed that an increased fluoride exposure was a risk factor for KOA (WF: OR = 1.318, 95% CI 1.162–1.495, p < 0.001; UF: OR = 1.210, 95% CI 1.119–1.310, p < 0.001). After adjusting for covariates, the risk of KOA in the 4th quartile (Q) of WF was twice that of the 1st Q (OR = 2.079, 95% CI 1.448–2.986, p < 0.001). The risks of KOA in the 2nd Q, 3rd Q and 4th Q of UF were 1.6, 1.5, and 2.9 times higher than in the 1stQ (OR = 1.597, 95% CI 1.066–2.393, p = 0.023; OR = 1.560, 95% CI 1.043–2.333, p = 0.030; OR = 2.897, 95% CI 1.957–4.288, p < 0.001). The population aged < 60 exposed to the 4th Q of WF (or UF) had a higher risk than the population exposed to the 1st Q of WF (or UF) (OR WF = 1.958, 95% CI 1.249–3.070, p = 0.003; OR UF = 2.923, 95% CI 1.814–4.711, p < 0.001). With increasing UF by Q, the male had a risk of KOA. In conclusion, excessive fluoride dose in drinking water could increase the risk of KOA. Especially, the population with aged < 60, male and obesity more likely to having KOA when they exposed to same higher fluoride.