The variability of selenium and sulphur and the impact of creatinine in blood and urine of humans

Background Intake of selenium (Se) and sulphur (S) is mainly through meat and fish. This is also the case for creatine, which is broken down into creatinine (Crea). Objectives Objectives were to assess variability of Se and S in urine and blood, assess diurnal variation and associations with Crea in urine (U-Crea). Methods Urine was collected at six fixed times for 24 h, and repeated one week later among 29 males and 31 females. Blood was collected at both occasions. Results Mean 24 h urinary excretions of S (U-S24 h) and Se (U-Se24 h) on the first sampling day were 756 mg and 23 µg, respectively. U-S24 h and U-Se24 h were highly correlated (r = 0.75; p < 0.001). Diurnal variation in the urinary excretion rate (ER) of S and Se was associated with urinary flow rate (UFR). Mean urinary concentrations of S and Se varied substantially during the day, except Crea adjusted concentrations. The 24 h U-Crea excretion was associated with U-S24 h (r = 0.81; p < 0.001) and U-Se24 h (r = 0.60; p < 0.001). The U-Crea ER were associated with those of S (r = 0.74; p < 0.001) and Se (r = 0.83; p < 0.001). The highest intraclass correlation coefficients (ICC) for Se was for the blood cellular fraction (0.898) and U-S24 h (0.529) for S. Conclusions The urinary S and Se ER were...