I would never worry about overdosing on selenium or zinc, especially if over age 40. Its not what you take, its what you absorb, and the older you are the less you absorb,thus, you could easily double your intake.

If you are worried about getting too much iron, just take extra antioxidants and/or become a blood donor.

A multivitamin is not a good way to get minerals for two reasons. First, multivitamins don't contain all necessary minerals and secondly, humans are not designed to absorb rocks. Full spectrum colloidal minerals is a much better way to get your mineral cofactors.

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Let Food Be Your Medicine And Medicine Be Your Food.(Hippocrates)