Daily variations in human plasma fluoride concentrations

This study investigated the variations in human plasma fluoride concentrations ([F]) and sought to determine the causes. Five subjects (27–33 years old) received a low-F diet during the 5 days of the study. Plasma samples and urine were collected every 3 h from 8 a.m. to 8 p.m. F, PTH, Ca and P were analyzed with the electrode, by chemiluminescence, AAS and colorimetry, respectively. A trend for the plasma [F] was found. The peak [F], 0.55 ± 0.11 μmol L−1, occurred at 11 a.m. and the lowest [F], 0.50 ± 0.06 μmol L−1 occurred between 5 and 8 p.m. Plasma [F] were positively correlated with urinary F excretion rates and with serum PTH levels, but not with the Ca or P levels. Serum PTH levels were positively correlated with urinary F excretion rates and negatively correlated with plasma Ca. The results suggest that the renal system seems to control the daily fluctuations in plasma [F].