|
Zinc (from German zink) is a chemical element in the periodic table that has the symbol Zn and atomic number 30.
Biological role
Zinc is an essential element, necessary for sustaining all life. It is estimated that 3000 of the hundreds of thousands of proteins in the human body contain zinc. In addition, there are over a dozen types of cells in the human body that secrete zinc ions, and the roles of these secreted zinc signals in medicine and health are now being actively studied. Intriguingly, brain cells in the mammalian forebrain are one type of cell that secretes zinc, along with its other neuronal messenger substances. Cells in the salivary gland, prostate, immune system and intestine are other types that secrete zinc.
Food sources
Zinc is found in oysters, and to a far lesser degree in most animal proteins, beans, nuts, whole grains, pumpkin seeds and sunflower seeds. Phytates, which are found in whole grain breads, cereals, legumes and other products, have been known to decrease zinc absorption. Clinical studies have found that zinc, combined with antioxidants, may delay progression of age-related macular degeneration, but the effect is extremely small and not likely to be clinically important. Significant dietry intake of zinc has also recently been shown to impede the onset of flu. Soil conservation analyzes the vegetative uptake of naturally occurring zinc in many soil types.
Zinc deficiency
Zinc deficiency results from inadequate intake of zinc, or inadequate absorption of zinc into the body. Signs of zinc deficiency includes hair loss, skin lesions, diarrhea, wasting of body tissues, and, eventually, death. Eyesight, taste, smell and memory are also connected with zinc and a deficiency in zinc can cause malfunctions of these organs and functions. Congenital abnormalities causing Zinc deficiency may lead to a disease called Acrodermatitis enteropathica.
Obtaining a sufficient zinc intake during pregnancy and in young children is a very real problem, especially among those who cannot afford a good and varied diet. Brain development is stunted by zinc insufficiency in utero and in youth. Teenage boys require 11 milligrams of zinc.
There is zinc in semen. As much as 0.25 milligrams of zinc will be found in 1 mL of seminal fluid. In fact, one of the methods used to test for semen in suspicious spots at a crime scene is to use a test for zinc (Hoof et al., Forensic Sci Int., 1992, 53:135).
Zinc toxicity
Even though zinc is an essential requirement for a healthy body, too much zinc can be harmful. Excessive absorption of zinc can also suppress copper and iron absorption. On the other hand, the free zinc ion in solution is highly toxic to plants, invertebrates, and even vertebrate fish. The Free Ion Activity Model (FIAM) is well-established in the literature, and shows that just micromolar amounts of the free ion kills some organisms. A recent example of 6 micromolar killing 93% of all daphnia in water is in Muyssen et al., (Aquat Toxicol. 2006). Swallowing a penny (98% zinc) can also cause damage to the stomach lining due to the high solubility of the zinc ion in the acidic stomach (Bothwell and Mair, PEDIATRICS 2003).
Psoriasis
Ionic zinc is a potent antimicrobial, used since 2500 BC in topical creams. Calamine lotion, diaper creams, and dandruff treatments are just some of the common antimicrobial applications. At low concentrations, zinc ions promote wound healing. Zinc ions also directly stimulate zinc receptors on skin cells, promoting wound healing.
Immune system
Zinc salts are effective against pathogens in direct application. Gastrointestinal infections are also strongly attenuated by ingestion of zinc, and this effect could be due to direct antimicrobial action of the zinc ions in the GI tract, or to absorption of the zinc and re-release from immune cells (all granulocytes secrete zinc) or both.
The direct effect of zinc (as in lozenges) on bacteria and viruses is also well-established, and has been used since at least 2000 BC, from when zinc salts in palliative salves are documented. However, exactly how to deliver zinc salts against pathogens without injuring one's own tissues is still being investigated.
|
