I certainly agree that food would be better then any supplementing if that food would be grown on minerals and other nutrients rich soil. There is some info on do and don't of zinc supplementing, etc., on this website ://www.nlm.nih.gov/medlineplus/druginfo/natural/982.html. From my own experience (long time ago), I developed white spots on my fingernails after taking 50,000 IU of vit A a day for approximately three weeks. I read that vit A interact with Zinc and that white spots on the fingernails might indicate Zinc deficiency. When I lowered vit A to 10,000 IU a day and took Zinc supplement all white spots disappeared.