Earlier results regarding the in vitro and in vivo effects of zinc on δaminolaevulinic acid dehydratase (ALAD) activity in red blood cells were confirmed in healthy human subjects after oral intake of zinc for 12 weeks. In one group of seven healthy adults, oral intake of zinc, as the sulphate salt (2.07 mmol zinc/day) for 6 weeks, resulted in a 44% increase in the activity of ALAD in erythrocytes. Plasma zinc levels also increased during the experimental period and reached a maximum of 29 μmol after 6 weeks and remained constant thereafter. In another group, the intake of zinc in a lower dose, (0.69 mmol zinc/day) for 12 weeks, showed a similar tendency, although the increase in the enzyme activity, as well as the plasma zinc levels, was relatively much less. The plasma copper levels decreased significantly in the second group after the zinc intake and reached a low value of 11 μmol at the end of the experimental period. The Cu:Zn ratio also decreased considerably towards the end of the experiment. The Cu:Zn ratio in the plasma seems to be a more valuable indicator of zinc status than plasma zinc levels alone. © 1979 Informa UK Ltd All rights reserved: reproduction in whole or part not permitted.
