Circadian variations in plasma zinc and cortisol in man.

Circadian variations of zinc and cortisol concentrations in plasma were studied in six healthy adult men. Three of them were tested over two different 24-h periods. Results were analyzed by computerizing a best-fit curve for each 24-h profile. Plasma zinc displayed a morning peak between 8.00 and 9.00 a.m. followed by an almost linear decline throughout the day with lowest values observed shortly before 6.00 p.m. A transitory increase occurred between 6.00 p.m. and 8.00 p.m. followed by a slow decrease reaching its nadir around midnight. Thereafter zinc increased steadily until 8.00 a.m. A similar profile was observed in a seventh subject who was undergoing therapeutic starvation for obesity (fifth day of the starvation period). In all subjects the time course of plasma cortisol fluctuations paralleled that of zinc. Our results confirm the existence of a circadian rhythm in plasma zinc independent of zinc intake and temporally related to the circadian rhythm of cortisol.