Subclinical excess may contribute to a wide variety of diseases. GI side effects are common with iron supplementation. On the other hand, absorption is best on an empty stomach. Ferrous iron is 1 and to 15 times better absorbed than ferric iron. Excessive calcium supplementation can reduce iron absorption.
Cobalt competes with iron for absorption.
Coffee, tea, milk, soy, tannins, zinc and manganese may reduce iron absorption while protein and particularly vitamin C enhances it. Absorption may be impaired with hypochlorhydria. Vitamin A deficiency impairs iron mobilization and utilization in the body. May increase cholesterol and triglyceride levels. Magnesium citrate is more soluble and bioavailable than magnesium oxide.