Diurnal variations of zinc, copper and magnesium in the serum of normal fasting adults.

Serum levels of copper, magnesium and zinc exhibit circadian rhythms in physiologically normal subjects eating normally. The same study was repeated with fasting subjects in order to determine the effect of daily food intake on these fluctuations. Blood samples were taken at 3 hour intervals, from 6 h to 18 h. Copper and magnesium no longer exhibit circadian rhythms in fasting subjects. In the case of zinc, however, a particularly interesting rhythm is observed, with a drop at 9 h and 15 h and an abrupt increase at 18 h.