>>34704568"Zinc is one of the most thoroughly researched and commonly deficient minerals. About a thousand papers are published each year indicating its value for a variety of conditions. The best-absorbed forms of zinc include zinc picolinate, amino ‘acid chelate, citrate and gluconate. Zinc supplementation is relatively non-toxic. In doses of 2,000mg symptoms of nausea, vomiting, fever and severe anaemia have been reported. Small amounts of zinc, particularly in the form of zinc sulphate, can act as an irritant in the digestive tract when taken on an empty stomach. There is also some evidence that zinc, at levels of 300mg per day, may impair rather than improve immune function. It is generally considered safe to supplement up to 50mg per day.
Zinc is an iron, manganese and copper antagonist therefore an adequate intake of these minerals is advisable if large amounts of zinc are taken over a long period of time. Manganese is very poorly absorbed and therefore it is generally advisable to supplement half as much manganese as zinc if more than 20mg of zinc is supplemented per day. The normal requirement for zinc is about ten times that of copper. Since the average intake of copper for those on a healthy diet is in the order of 2mg, those supplementing more than 20mg of zinc may be advised to add 1mg of copper for each additional 10mg of zinc. It is also best to ensure that at least 12mg of iron is supplemented when taking more than 20mg of zinc."
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http://www.ion.ac.uk/information/onarchives/minerals 
