Zinc requirements, the recommended dietary allowance and the reference dose

1. The 1989 zinc RDA is not congruent with many of the estimates of requirements determined by factorial or metabolic methods. 2. The proposed zinc RfD was based on the finding of lower activity of E-SOD after the administration of zinc in a form that might be consumed in an unprescribed medication. This lower activity was taken as a marker of toxicity. 3. The proposed zinc RfD is incompatible with the 1989 RDA and the 1973 WHO FER or requirements published by King & Turnland (23). 4. A calculation of the RfD that accounts for bioavailability gives RfD values for OTC medications, and high and low bioavailability diets of 0.25, 0.83 and 1.66 mg.kg-1.d-1, respectively.