Zinc is an important element for human metabolism and health. After Iron (Fe) it is the second most abundant element in our body. The importance of this element covers many body processes from the regulation of gene expression to protein synthesis and structure. Zinc is the co-factor in as many as 100 enzymatic reactions in the human body. If we have a well rounded diet we acquire Zn naturally from beef, poultry, seafood and grains. In a 2002 survey some 2.5 percent of those adults surveyed stated they took Zn as a dietary supplement daily. Also noted in epidemiological studies is that zinc deficiency accounts for a global death rate of 1.8-million individuals each year. This is mostly seen in the severely malnourished. Other symptoms of Zn deficiency are growth retardation, delayed puberty, erectile dysfunction, loss of hair, nail dystrophy and hypogonadism in males.
Zinc has been used to treat childhood diarrhea, age related macular degeneration, prevention of upper respiratory infections and in wound care. Zinc with the co-factor of Vitamin C is intricately involved in the process of development of collagen and connective tissue repair. Additionally, it has been associated with reduction of rapid progression of HIV disease in those who are Zn deficient and in treating those with Wilson disease (a Copper (Cu) metabolism disorder) as it competes for protein binding sites with Cu. Zinc is important to T-cell maturation (a component of our immune system) as it is a co-factor in the production of thymulin a thymic hormone essential for T-cell production and function. There is some controversy as to whether Zn lozenges help treat upper respiratory infections (URI) already acquired versus preventing them, but more research is needed.
There are issues with taking too much Zn. A safe dose is around 20 to 30 mg per day. The upper limit being 40mg/d for most people for long term use. Too much zinc can inhibit the absorption of copper as it competes for its absorption in the body, it can suppress the immune system, decrease HDL-C (good cholesterol) and cause a hypochromic microcytic anemia. It can also result in nausea, vomiting and abdominal cramping. Zn absorption is inhibited by concomitant administration of iron (Fe) and large intakes of phytates found in grains and legumes. So these should be taken separately when Zn supplements are taken.
Not all Zn supplements are equal. For example Zinc acetate has only 30% of the elemental zinc by volume where Zinc sulfate has 23% and Zinc oxide has 80%. So of you take 25 mg of Zinc acetate you are only getting 7.5 mg of elemental Zn, but if you take 25 mg of Zinc oxide you receive 20mg of Zn. So read labels carefully on your selection of zinc supplements.
To slow the progression of Age Related Macular Degeneration (ARMD) a study show effectiveness in people over 55-years of age with the combination of 80mg of Zn, 2mg of copper and in combination of Vitamin C (500mg), Vitamin E (400IU), and Beta-carotene (15mg) acting as antioxidants. Incidentially, zinc holds antioxidant properties in and of itself.
Zinc containing foods
There are studies to show the importance of Zn in human reproduction. Zn in important in females for fertility as well as males. Zinc can aid in the production of testosterone, increase sperm cell counts and help in the uncoupling of testosterone from binding proteins. Additionally Zn can act to prevent the aromatization of testosterone to estrogens and conversion of testosterone to DHT (undesirable in men).
(c) 2009 References:
Saper, RB, et, al. Zinc: An Essential Micronutrient, Am Fam Physician. 2009;79(9):768-772