Clinical significance of diurnal variation in the estimation of plasma zinc

Summary In the past there has been controversy over the existence of a significant diurnal variation of plasma zinc. For clinical use one is not only interested in the possible existence of such a varying pattern, but whether it is of sufficient magnitude that samples should be taken at standardized times of the day. Plasma zinc levels were estimated throughout the day (in a period encompassing normal laboratory working hours) in sixteen healthy male volunteers. There was a significant decrease in the mean plasma zinc level from 08:00 to 19:00 of 33%, (P < 0·001). Even over the relatively short time interval of 08:00–10:00 a significant decrease in plasma zinc occurred (11%; P < 0·05).