Objective:To investigate the relationship between plasma fluoride content, daily calcium intake and blood cell parameters in children and adolescents.Methods:This study was based on the National Health and Nutrition Examination Survey (NHANES) database of the United States from 2013 to 2016, with 3 684 children and adolescents aged 6 - 19 as the research subjects. Information on plasma fluoride content, daily calcium intake and blood cell parameters from the database were collected. Non-linear relationships between plasma fluoride content, daily calcium intake and blood cell parameters were analyzed using restricted cubic splines. If there was a non-linear relationship, the optimal inflection point was calculated using threshold/saturation effect analysis method. Subsequently, multiple linear regression models were used to analyze the associations among the three, and the modification effect of daily calcium intake (binary classification, stratified by median daily calcium intake) on the association between plasma fluoride content and blood cell parameters was analyzed.Results:There was no non-linear relationship between plasma fluoride content and white blood cell count, hemoglobin content and platelet count ( Pnon-linear > 0.05), but there was a non-linear relationship between plasma fluoride content and erythrocyte count and hematocrit ( Pnon-linear < 0.001). After adjusting for confounding factors, the optimal inflection points of the effects of plasma fluoride content on erythrocyte count and hematocrit were 0.54 and 0.31 μmol/L, respectively. There was no non-linear relationship between daily calcium intake and blood cell parameters ( Pnon-linear > 0.05). After adjusting for confounding factors, for every 1 μmol/L increase in plasma fluoride content, the white blood cell count increased by 0.49 × 10 9/L ( P = 0.009). There was a saturation effect in the association between plasma fluoride content, erythrocyte count and hematocrit: when plasma fluoride content was < 0.54 μmol/L, the erythrocyte count decreased by 0.46 × 10 12/L for every 1 μmol/L increase ( P < 0.001). When plasma fluoride content was < 0.31 μmol/L, the hematocrit decreased by 6.29% for every 1 μmol/L increase ( P = 0.006). The above associations were not statistically significant when plasma fluoride content was higher than the optimal inflection points ( P > 0.05). After stratification according to the median daily calcium intake, in the low-calcium group (daily calcium intake < 0.87 g), for every 1 μmol/L increase in plasma fluoride content, the white blood cell count increased by 0.77 × 10 9/L ( P = 0.001). When plasma fluoride content was < 0.54 μmol/L, the erythrocyte count decreased by 0.41 × 10 12/L for every 1 μmol/L increase ( P = 0.002). When plasma fluoride content was ≥0.54 μmol/L, erythrocyte count decreased by 0.47 × 10 12/L for every 1 μmol/L increase ( P < 0.001). When the plasma fluoride content was < 0.31 μmol/L, the hematocrit decreased by 8.29% for every 1 μmol/L increase ( P = 0.011). The above associations were not statistically significant in the high-calcium group (daily calcium intake ≥0.87 g, P > 0.05). There was an interaction of daily calcium intake and plasma fluoride content on platelet count ( Pinteraction = 0.070), as demonstrated by an increase in platelet count of 12.68 × 10 9/L ( P = 0.013) in the low-calcium group and a decrease in platelet count of 9.05 × 10 9/L ( P = 0.035) in the high-calcium group for every 1 μmol/L increase in plasma fluoride content. Conclusions:The blood cell parameters of children and adolescents are closely related to plasma fluoride content, but not directly related to daily calcium intake. However, the correlation between plasma fluoride content and blood cell parameters varies among different calcium intake populations, and daily calcium intake can modify the association between plasma fluoride content and platelet count.