Answer to Question 1
Dietary factors: Bioavailability of zinc from animal sources is greater than from plant sources, and acidic substances (such as vitamin C) increase its absorption. Because zinc absorption relies on the same transport protein as several other divalent cations (e.g., Fe2+, Cu2+, and Ca2+), high intakes of these minerals can decrease its bioavailability.
Genetic factors: People with acrodermatitis enteropathica, a genetic disorder, have a defect in the protein needed to transport zinc into the enterocyte. The defective protein is less able to transport zinc, causing it to be lost in the feces. This disease is characterized by severe zinc deficiency even when zinc is adequate in the diet, and is usually seen in the first few months of life. The treatment is life-long zinc supplementation.
Answer to Question 2
All three of these minerals are involved in protecting the body from oxidative damage. Copper and manganese are both cofactors for superoxide dismutase, an enzyme that protects cells from free radicals. Selenium is incorporated into selenomethionine, and subsequently used to make proteins called selenoproteins. One group of enzymatic selenoproteins called glutathione peroxidases has redox functions, protecting against oxidative damage from free radicals.
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