Influence of Oral Zinc Intake on Whole Blood and Plasma Levels of Copper

Abstract

Plasma and whole blood concentrations of zinc and copper were analysed in three groups of human volunteers who consumed different levels of zinc as zinc sulphate (Zn SO4, 7H2O). The first group consumed 135 mg, the second group 90 mg and the third group 45 mg zinc daily for twelve weeks. In all three studies, age-matched healthy subjects served as controls. Blood samples were collected prior to, during and after the experimental period. On an average 10 – 12 samplings were made in each study.Our results showed that after a latent period of 2 - 4 weeks, the plasma zinc started to increase and reached maximum level (25 – 30 μimol/1)after six weeks and thereafter remained almost constant throughout the experimental period. The zinc levels returned to initial levels (14 pmol/1) two weeks after the termination of oral zinc intake. Similarly, we observed an increase in the concentration of zinc (140 μmol/l) in erythrocytes after two weeks from the start of the experimental period. This increase, however, was not as significant as that was found in plasma. Further, we did not observe any changes in the erythrocyte zinc after the initial increase. Along with the. increase of plasma zinc concentrations, the revels of copper in plasma started to decrease and reached significantly low levels (11 μmol/l) towards the end of the experimental period. The copper:zinc quotient In plasma which is normally around 1 became 507 lower than the initial values during the last stage of the zinc intake. We did not observe any changes in whole blood levels of copper during zinc intake.Our results on the whole indicate that prolonged oral zinc intake may influence the absorption and distribution of copper. This may be of importance in view of the fact that the dietary intake of copper in affluent countries is low as compared to the recommended levels.