General Informations on Zinc for Consumers
What is zinc?
Zinc is a metal just like copper and iron and its pure form has a metallic colour, somewhat resembling lead. Anyway, even if it may appear strange, zinc is also used by so many proteins contained in the cells that it is impossible to find a living organism without zinc.
Our body contains about 2 to 3 grams of zinc distributed in all organs, tissues, fluids and secretions. Our cells require zinc for the proper function of more than 300 proteins involved in a multitude of biochemical reaction which sustain particularly our immune system, neuronal activity normal growth and development during pregnancy, childhood and adolescence.
In addition, zinc is necessary for wound healing and helps maintain your sense of taste and smell.
What happen if zinc in our body is insufficient?
Being so many the functions of zinc in our organism, there are also so many adverse effects that have been observed during zinc deficiency (1). They include immune dysfunction, increased incidence of infections, hypogonadism, oligospermia, anorexia, growth retardation, hair loss, diarrhea, delayed sexual maturation, impotence, eye and skin lesions, loss of appetite, weight loss, delayed healing of wounds, taste abnormalities and mental lethargy.
Moderate to severe zinc deficiency is prevalent in developing countries, but it is rare in industrialized countries. However, several diseases and situations predispose to zinc deficiency (2), such as acrodermatitis enteropathica, alcoholism, malabsorption (including sprue, cystic fibrosis and short bowel syndrome), thermal burns, total parenteral nutrition without zinc supplementation, inflammatory bowel disease (including Crohn’s disease and ulcerative colitis), sickle cell anemia, Down’s syndrome, HIV and certain drugs, such as diuretics, penicillamine, sodium valproate and ethambutol.
Strict vegetarians are also at risk for zinc deficiency because their diet usually contain low amount of zinc and large amount of grains and legumes which contain high levels of phytic acid, a compound that strongly reduce the intestinal absorption of zinc (3). For additional informations on this last aspects you con look at the web page dedicated to zinc (http://www.vegsoc.org/info/zinc.html) of the Vegetarian Society web site.
What about elderly subjects and zinc deficiency?
Elderly subjects are at high risk for zinc deficiency also in industrialized countries because zinc intake in many of the elderly may be suboptimal, due to inadequate mastication and malabsorption. Reported values on the fractional absorption of zinc in the elderly have been quite variable but aging can lead to mild or even moderate zinc deficiency also because it is often combined with age related diseases and the concomitant use of certain drugs.
In addition, latest advance in biochemical research reports that zinc deficiency in the elderly may partially originate from dysfunction of proteins which regulate its homeostasis (4). Zincage Project is actually investigating many of these aspects.
What foods provide zinc?
Zinc is found in a wide variety of foods. Oysters contain more zinc per serving than any other food, but generally, meat (especially liver) and fish, especially shellfish, codfish and bluefish, are an optimal source of zinc as well as beans, nuts, and some dairy products.
Phytates, which are found in whole grain breads, cereals, legumes and other products, can decrease zinc absorption despite some of these foods could potentially be good source of zinc. You can find tables and other updated informations on food sources for zinc and other nutrients at the web-site of the Agricultural Research Service: http://www.ars.usda.gov/main/main.htm
What is the recommended daily allowance?
The latest recommendations for zinc intake are given in the new Dietary Reference Intakes developed by the Institute of Medicine (http://www.iom.edu/ ). Dietary Reference Intakes (DRIs) reports reference values used for planning and assessing nutrient intake for healthy people. The Recommended Dietary Allowance (RDA), one of the DRIs, is the average daily dietary intake level that is sufficient to meet the nutrient requirements of nearly all (97-98%) healthy individuals (1).
For infants 0 to 6 months, the DRI is in the form of an Adequate Intake (AI), which is the mean intake of zinc in healthy, breastfed infants. The AI for zinc is 2.0 milligrams (mg) per day for infants from 0 through 6 months; 3 mg/day for infants from 7 months to 3 years; 5 mg for children from 4 to 8 years; 8 mg for children from 8 to 13 years; 11 mg for males and 9 mg for females from 14 to 18 years; 11 mg for males and 8 mg for adults.
In elderly, it is generally considered appropriate 10-11 mg for male and 9-10 mg for females. Among the elderly, zinc intake is often about 9 mg a day, because food consumption -especially of proteins- is often reduced with aging, so the elderly need to pay special attention to their zinc intake.
It is necessary to take zinc supplements?
Very low zinc is bad as well as too much! There is a general growing concept that taking zinc supplements can benefits health and well being especially for elderly people, but self prescription of zinc supplements without the advice of a physician is not advisable.
Like all minerals in the body, there are problems associated with both zinc deficiencies and excesses. You should be able to get all the zinc you need by eating a varied and balanced diet. Anyway, zinc supplementation, when advisable can lead to some benefits especially in older people.
Zinc supplements given to individuals with low circulating zinc levels increase the numbers of T-cell lymphocytes circulating in the blood and improves the ability of lymphocytes to fight infection (4). Zinc supplementation is generally given to help heal skin ulcers or bed sores even if it do not increase rates of wound healing when zinc levels are normal (5). Zinc treatment seems very useful also to reduce the severity and duration of cold symptoms and in treating macular degeneration and cataract but additional research is still needed to confirm these results. Results of zinc supplementation in elderly have been quite variable; some reported a normalization of zinc in granulocytes and lymphocytes and improvement in various immune parameters (6), others did not found any detectable benefits (7).
Excess of zinc may instead impair immune functions and lead to a deficiency in other essential metals like copper (8). It has also been suggested that excess zinc is atherogenic and may have some toxic effects.
Therefore, before taking any zinc supplement it is highly advised to perform at least the laboratory measurement of plasma/serum zinc concentration considering 10,5 mM (for adults) as a threshold value indicating a possible zinc deficiency, which should be carefully weighted by the physician evaluating the presence of other risk factors (drug intake, dietary intake, disease, age etc.). It is also advisable to know the erythrocytes and leukocytes zinc concentration that is more useful to evaluate the presence of zinc deficiency.
LINKS:
This is the site of the International Zinc Association (Brussels, Belgium). Here you can find several press releases with a section dedicated to zinc health and nutrition. The site is continuously updated and comprehensive of the “zinc world”.
This is the official site of the American Zinc Association (Washington, USA). There are many pages dedicated to the role of zinc in health and well being subdivided in sections for men’s health, women’s health and children/adolescents health. You can download also an educational video.
3) http://ods.od.nih.gov/factsheets/cc/zinc.html
A well done and useful site from the National Institute of Health (Bethesda, Maryland, USA), Office of Dietary Supplements (http://ods.od.nih.gov), where to find table and facts about zinc with several references. It is also possible to download a printable pdf version.
4) http://lpi.oregonstate.edu/infocenter/minerals/zinc/
Another well done and reviewed site from the Linus Pauling Institute Micronutrient Information Center (Oregon State University) which provides scientific information on health aspects of micronutrients and phytochemicals for the general public. Here you can find among others some helpful informations on prevention of disease related to zinc deficiency.
5) http://www.eatwell.gov.uk/healthydiet/nutritionessentials/vitaminsandminerals/zinc/
This site from the Food Standards Agency (UK) contains many consumer’s advice and informations on several vitamins and minerals. There are little essential written information on zinc but here you can download a comprehensive scientific report, from an Expert Group on Vitamin and Mineral, focused on Studies of particular importance for the risk assessment of zinc excess.
6) http://www.pdrhealth.com/drug_info/nmdrugprofiles/nutsupdrugs/zin_0281.shtml
A web page dedicated to zinc, health and well being from Thompson Corporation. Here you will find, among many other informations, a section dedicated to the action, pharmacology and pharmacokinetics of zinc.
7) http://www.vegsoc.org/info/zinc.html
This is a sheet from the web site of the Vegetarian Society with informations on dietary sources of zinc for vegetarians.
8) http://www.gaa.com.au/theenvironment_tiozfhh.html
Some brief and essential informations on zinc from the Galvanizer Association of Australia.
9) http://www.atsdr.cdc.gov/tfacts60.html
A site from the Agency for Toxic Substances and Disease Registry (ATSDR) where you can find many information on the toxic effects of excess zinc.
10) http://www.ctds.info/zinc1.html
A part of a site dedicated to Connective Tissue Disorders. In this site you will very useful informations concerning with Zinc deficiency
11) http://www.medicinenet.com/zinc_lozenges_as_a_cold_remedy/article.htm
Facts about zinc focused on the benefits of zinc Lozenges for common cold. The site is from MedicineNet.com (http://www.medicinenet.com/script/main/hp.asp ) a site dedicated to Doctor-Produced Health and Medical Information for the public.
(1) Institute of Medicine. Food and Nutrition Board. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. National Academy Press. Washington, DC, 2001.
(2) Prasad AS. Zinc deficiency in women, infants and children. J Am Coll Nutr 1996;15:113-120.
(3) Wise A. Phytate and zinc bioavailability. Int J Food Sci Nutr 1995;46:53-63.
(4) Mocchegiani E, Muzzioli M, Giacconi R. Zinc and immunoresistance to infection in aging: new biological tools. Trends Pharmacol Sci. 2000 Jun;21(6):205-8.
(5) Anderson I. Zinc as an aid to healing. Nurs Times 1995;91:68, 70.
(6) Prasad AS, Fitzgerald JT, Hess JW, Kaplan J, Pelen F, Dardenne M. Zinc deficiency in elderly patients. Nutrition. 1993 May-Jun;9(3):218-24.
(7) Swanson CA, Mansourian R, Dirren H, Rapin CH. Zinc status of healthy elderly adults: response to supplementation. Am J Clin Nutr. 1988 Aug;48(2):343-9.
(8) Chandra RK. Nutrition and the immune system from birth to old age. Eur J Clin Nutr. 2002 Aug;56 Suppl 3:S73-6.