Circadian variations in serum zinc (Zn) concentrations: correlation with blood ionized calcium, serum total calcium and phosphate in humans.

Serum zinc (Zn) concentrations were determined in sequentially drawn blood samples from six healthy adult males. Each subject had blood sampling performed every 30 minutes for 24 hours. Mean Zn concentrations at each time point (n = 6, 48 time points) were plotted and fitted by a polynomial regression of the data against time. A "U" shaped curve was derived; we found peak Zn levels at 9:30 AM, a midtrough at 8 PM and a peak-trough difference of 19 micrograms/dl. Correlation with a similarly derived 24-h ionized calcium pattern was strikingly high, r = .923, p less than .001. An intermediate correlation between the Zn and phosphate patterns was observed, r = -.493, p less than .01; and no significant correlation occurred between Zn and total calcium rhythms, r = .167. These data conclusively demonstrate the presence of a circadian rhythm in serum Zn in healthy adult males. Furthermore, the high correlation between the Zn and ionized calcium patterns suggests a common regulator.