Only a few occurrences of acute zinc poisoning have been reported. The
toxicity
   signs are nausea, vomiting, diarrhoea, fever, and lethargy and have 
been
   observed after ingestion of 4-8 g (60-120 mmol) zinc. Long-term zinc
intakes
   higher than the requirements could, however, interact with the
metabolism of
   other trace elements. Copper seems to be especially sensitive to high 
zinc
   doses. A zinc intake of 50 mg/day (760 mmol) affects copper status
indexes, such
   as CuZn-superoxide dismutase in erythrocytes (37, 38). Low copper and
   ceruloplasmin levels and anaemia have been observed after higher zinc
intakes
   450-660 mg/day (6.9-10 mmol/day) (39, 40). Changes in serum lipid
pattern and in
   immune response have also been observed in zinc supplementation studies
(41,
   42). Because copper also has a central role in immune defence, these
   observations call for caution before large-scale zinc supplementation
programmes
   are undertaken. Any positive effects of zinc supplementation on growth 
or
   infectious diseases could be disguised or counterbalanced by negative
effects on
   copper-related functions.

   The upper level of zinc intake for an adult man is set at 45 mg/day 
(690
   mmol/day) and extrapolated to other groups in relation to basal
metabolic rate.
   For children this extrapolation means an upper limit of intake of 23-28
mg/day
   (350-430 mmol/day), which is close to what has been used in some of the
zinc
   supplementation studies. Except for excessive intakes of some types of
seafood,
   such intakes are unlikely to be attained with most diets. Adventitious 
zinc in
   water from contaminated wells and from galvanized cooking utensils
could also
   lead to high zinc intakes.