Zinc is an essential trace element for humans, animals and plants. It is essential for human health.
What is Zinc?
It is a metallic chemical element with the symbol Zn and atomic number 30. It is the fourth most common metal in use, trailing only iron, aluminium and copper in annual production. It is used in galvanising, in alloys, in coinage, in batteries, as a pigment in paints, as a deodorant and in many other commercial situations.
Here we are concerned with its role in the human body and its role in the healthy functioning of the body.
The Biological Role of Zinc
Zinc is an essential element, necessary for sustaining all life. It is found in virtually every tissue in the human body: it is in organs, tissues, bones, fluids and cells. It is estimated that the body contains 2-3 grams of zinc. Muscles and bones contain 90% of the body’s zinc. Particularly high concentrations of zinc are in the prostate gland and semen. Zinc is part of some 3,000 of the hundreds of thousands of proteins in the body. There are over a dozen types of cells in the human body that secrete zinc ions. These are now considered neuro-transmitters. Cells in the salivary gland, prostate, immune system and intestines are other types that use zinc signalling.
Zinc plays a crucial role in some 200 or more enzymes. These enzymes depend on zinc to work properly. Zinc is also an activator of certain enzymes such as carbonic anhydrase (important in the transportation of carbon dioxide in vertebrate blood) and superoxide dismutase (the important antioxide enzyme).
Many of the enzymes which require zinc are involved in the synthesis of DNA and RNA, without which cells cannot reproduce themselves and growth and development would be impossible.
Zinc is necessary to make many hormones, including those linked to the immune system and those that control growth and testosterone.
Zinc is also essential for the metabolism of vitamin A, an important antioxidant.
Zinc – Essential for Human Health
a) Zinc and the Immune System
A substantial decline in immune function can occur within 30 days of suboptimal zinc consumption. Lack of zinc results in reduced lymphocyte numbers (white cells central to the immune system) and the inability of certain types of lymphocytes, in particular T-Lymphocytes and natural killer T-cells, to function properly. Deficiency also leads to reduction in antibody production and hence a reduced resistance to infectious diseases, including pneumonia and diarrhoea, especially in children. The reason why zinc deficiency causes these problems is thought to be due to the inability of enzymes, essential to the development and functioning of the immune system, to operate properly without zinc. Zinc helps to reduce the severity and duration of the common cold and flu, due to its positive effect on the immune system.
b) Zinc and Skin, Hair and Nails
Zinc accelerates the renewal of skin cells. It promotes better healing of cuts and wounds, especially post-operatively. It is useful in the treatment of acne, psoriasis and neurodermatitis.
Zinc is important for healthy hair. Insufficient zinc levels may result in hair loss and hair that looks thin and dull and goes grey easily. Zinc protects against dandruff.
c) Zinc and Vision
High concentrations of zinc are found in the retina. With increasing age, the retinal zinc declines and this seems to play a role in age-related macular degeneration, which leads to partial or complete loss of vision. Zinc also protects against the development of cataracts.
d) Zinc and Taste, Smell and Appetite
Zinc activates areas in the brain that receive and process information from taste and smell sensors. Levels of zinc in the blood plasma, and zinc’s effect on other nutrients like copper and manganese, influence appetite and taste preference. Zinc is used in the treatment of Anorexia Nervosa.
e) Zinc and Growth and Cell Division
Zinc is especially important during pregnancy, for the growing foetus whose cells are rapidly dividing. Zinc is vital in activating growth – height, weight and bone development, in infants, children and teenagers.
f) Zinc and Fertility and the Prostate
Zinc plays a vital role in fertility.
In males, zinc protects the prostate gland from infection (prostatitis) and ultimately from enlargement (benign prostatic hypertrophy). Zinc helps maintain sperm count and mobility, and normal levels of testosterone.
In females, zinc can help treat menstrual problems and alleviate symptoms associated with the premenstrual syndrome.
g) Zinc and Diabetes
Some diabetics may be low in zinc because they do not absorb it well and also excrete it too quickly.
Zinc may also help with other problems that diabetics often have, such as slow wound healing and frequent infections.
h) Zinc and Memory
People with adequate levels of zinc do better in memory tests than those whose level is suboptimal.
Symptoms of Zinc Deficiency
Zinc deficiency results from inadequate intake of zinc and/or inadequate absorption of zinc into the body and/or excessive excretion of zinc.
Above, we’ve looked at how zinc is essential for human health. Another way of expressing this is to look at the symptoms of zinc deficiency:
· Slow growth, infertility and reduced sex drive and sexual maturation
· Frequent or severe infections
· Delayed wound healing and post-operative complications
· A wide variety of skin problems including acne and psoriasis
· Problems with hair and nails, including hair loss, dandruff and characteristic white spots on the finger nails
· Reduced appetite, possibly due to impaired taste and smell, which can lead to anorexia
· Poor dark adaptation
· Macular Degeneration and cataracts
· Psychiatric or behavioural problems, also sleep disturbance.
Causes of Zinc Deficiency
Zinc deficiency is a serious problem in many developing countries, being ranked as the fifth leading risk factor in causing disease, especially diarrhoea and pneumonia in children, which can lead to high mortality rates in these underdeveloped regions.
In Western countries, deficiency is generally found in those on restricted diets. These may include certain slimming diets, vegan diets, low protein diets and exclusion diets for food allergies or food intolerance.
The elderly are at more risk than the young, due to poorer absorption of nutrients from the gut with increasing age.
High fibre diets also interfere with zinc absorption, as does coeliac disease (gluten-sensitivity) and iron medication (since iron inhibits zinc absorption).
Zinc is lost from the body with excessive fluid loss (eg diuretic treatment), burns, chronic diarrhoea, and after trauma and surgery.
People who abuse alcohol often have a poor diet. Even moderate amounts of alcohol flush out the zinc stored in the liver and cause it to be excreted.
Food Sources of Zinc
We obtain zinc primarily from our food. The highest levels of zinc are found in oysters (25mg/100gm). To a far lesser degree, zinc is present in meat (especially red meat) and in most animal proteins (approximately 5mg/100 gm). Nuts, dairy products, cereal grains, beans, pumpkin seeds and sunflower seeds contain less, though significant, amounts of zinc (1-3mg/100gm). Vegetables have less (eg potatoes 0.3mg/100gm), and fruits the least amount (less than 0.1mg/100gm).
The bioavailability of zinc from plant-based foods is generally lower due to dietary fibre and phytates (found in whole grains and legumes) which inhibit the absorption of zinc.
A zinc supplement may be taken if the nutritional intake is insufficient.
How Much Zinc Do We Need?
The (US) recommended dietary allowance for zinc, from puberty onwards, is 11mg for males and 8mg for females, with higher amounts (up to 15mg) recommended during pregnancy and lactation.
Some authors recommend 15mg as the daily dose for men.
Children need 10mg daily
The most easily absorbed form of zinc is zinc gluconate. Other zinc salts such as picolinate and citrate are also good options. Zinc sulphate is not recommended, as it is likely to upset the stomach. Zinc oxide is not to be taken orally (it is useful in skin creams meant to block sunlight).
The (US) recommended ‘tolerable upper limit’ for zinc supplement is 40mg/day for adults over 19 years. They set the toxic level as greater than 150mg.
Doses up to 30mg/day (zinc gluconate 209mg equivalent to 30mg of zinc) are generally well tolerated. Higher doses may, rarely, cause gastrointestinal reactions including nausea, vomiting and cramps. High doses may impair the absorption of copper and iron.
Zinc is required for a huge range of bodily functions. Adequate levels are essential for the correct functioning of the immune system, growth and development and the antioxidant system.
Supplemental zinc, eg zinc gluconate, should be considered if the dietary intake of zinc is insufficient or if conditions leading to excessive zinc loss are present.
*Copyright 2009: The Huntly Centre.
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