Zinc is required for a huge range of bodily functions.  It is found in virtually every tissue in the body and is particularly important for the correct functioning of the immune system, growth and development, and the antioxidant system (see the page in our website on antioxidants: http://www.collectiveability.co.uk/science.antioxidants_.htm ).  The main way in which it is used in the body is as an essential component (known as a “cofactor”) for the functioning of a large number (over 70 so far identified) of enzymes, proteins which act as catalysts, enabling the body to carry out the chemical reactions essential for life.

 In this newsletter, I’ll talk about:

1.      Functions in the body

2.     Food sources and daily requirements

3.      Causes and symptoms of deficiency

4.      Some conditions which can be helped by zinc supplementation

5.      How and when to supplement.

 Functions:  The important antioxidant enzyme, superoxide dismutase (SOD), requires zinc, together with copper and manganese, to function.  Reduced activity of SOD has been linked to Alzheimers disease, rheumatoid arthritis, atherosclerosis and lung injury, especially in the elderly.  Zinc is also essential for the metabolism of vitamin A, another important antioxidant.  The exact methods by which zinc may carry out its antioxidant effects are described by S.R. Powell in a rather technical paper.

 With regard to the immune system, a substantial decline in immune function can occur within 30 days of suboptimal zinc consumption.  Lack of zinc has been found to cause reduced lymphocyte numbers (lymphocytes are a type of white blood cell which is central to the immune system) and inability of certain types of lymphocyte (T-lymphocytes and natural killer cells) to function properly.  Deficiency also leads to a reduction in antibody production and the ultimate result of this is reduced resistance to infectious diseases, at first very minor  but which, over the course of time can lead to life-threatening infections including diarrhoeal disease in children and urinary tract and pulmonary infections in the elderly.  The exact reasons why zinc deficiency causes these problems is not yet completely clear but it is thought that the inability of enzymes essential to the development and functioning of the immune system to operate without zinc is an important factor.

 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.  Therefore, it’s not surprising that zinc deficiency in children can result in stunted growth and impaired sexual development.         top of page

 Food sources and daily requirements:

The amount of zinc required daily is 9.5 milligrams for a man and 7 milligrams for a woman – similar to the daily iron requirement, except in women of childbearing age where iron requirements are greater.  High protein diets can interfere with absorbtion of zinc leading to a greater dietary requirement.

 Zinc is found in a wide range of foods, the richest sources being shellfish, animal proteins (meat, eggs & dairy produce), pulses, nuts and wholemeal grains.  White flour is a poor source, both because the zinc is mainly found in the outer layers of the grain and because the fibre in grain contains phytates, which inhibit the absorption of minerals.

Symptoms and causes of deficiency:

 Symptoms: 

·        Slow growth, infertility and reduced sex drive or delayed sexual maturation.

·        Frequent or severe infections including diarrhoea.

·        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 (night blindness).

·        Psychiatric or behavioural problems, also sleep disturbance.

 Causes:

Deficiency in diet:                                                                       top of page

 This is generally found in those on restricted diets, especially low protein diets.  These may include certain slimming diets, vegan diets, low protein diets (e.g. for those with kidney stones) and exclusion diets for food allergies.  A group particularly at risk are the elderly as their absorption of nutrients from the gut may be lower than in the younger people for whom the recommended dietary allowances (RDA) were established.  Furthermore, many elderly people eat less overall and, due to difficulty getting out may be more likely to eat long-life foods low in zinc and other essential nutrients.  Gershwin and Hurley have shown that many elderly people suffer from a significant degree of malnutrition.  Other groups which may have difficulty absorbing zinc from the gut are those on high fibre diets, people with coeliac disease and those taking iron tablets as iron interferes with zinc absorption.  Zinc deficiency is also common among famine victims and those prone to self-neglect e.g. alcoholics.

 Conditions in which zinc is liable to be lost from the body:

 This is mainly found in people with excessive fluid loss from the body.  These include those taking diuretics, on dialysis, with chronic blood loss (e.g. infections with gut parasites), suffering from burns, chronic diarrhoea, weeping skin conditions, ileostomy fluid loss and after surgery or trauma.

 Increased need for zinc:

This commonly occurs during growth spurts in childhood and puberty.  During pregnancy and lactation more is also needed to aid the development of the child’s immune system.  Care should be taken with iron supplements, commonly given to expectant mothers, as iron can inhibit zinc absorption.

Some conditions which may be helped by zinc supplementation:

 Here I’ve concentrated on a selection of conditions for which I’ve been able to find clear scientific evidence with references to a few papers out of the many thousands that have been published on zinc deficiency and supplementation.

Growth and development of infants.

Worldwide, the most common cause of deficient immunity is malnutrition (see Chandra RK); in Ethiopia, it has been found that zinc supplementation has improved growth rate and immunity in young children, while in the developed world, zinc deficiency has been linked to development of allergies.  Recent research in Poland has found that levels of zinc (and also selenium and copper) in the milk of breast-feeding mothers declined by about a factor of 10 during the first month, so zinc supplementation of breast feeding mothers would seem to be a good idea.

Susceptibility to infectious diseases.

The immune deficiency caused by zinc deficiency is most clearly seen in the infections which result from weakened defences.  These include diarrhoea in children, lung and urinary tract infections in the elderly, and infections with intestinal parasites.  In leprosy patients, also, supplementation with zinc has been found to improve their condition.

A lot of work has been done on the role of zinc deficiency in AIDS; for example, Mocchegiani and Muzzioli found that supplementation with zinc led to a striking reduction in the frequency of the, so called, "opportunistic" infections which are the actual cause of illness and death in AIDS patients.                            top of page

Skin conditions.

Children suffering from the hereditary disease acrodermatitis enteropathica, caused by an inability to absorb zinc from their food, suffer from hair loss and skin problems, as well as diarrhoea and defective growth and development.  These symptoms disappear when they are given high doses of zinc supplements (the small proportion they can absorb is then enough to keep them healthy).  More commonly, zinc supplementation has been found to be very helpful for eczema, acne and leg ulcers in the elderly.

Rheumatoid arthritis.

Rheumatoid arthritis is an inflammation of the joints caused by an "autoimmune" response, when the immune system mistakes friend for foe and directs "friendly fire" at one of its own components.  Where inflammation is found, free radicals will be present in abundance causing the damage and so high levels of antioxidants are needed to neutralise them.  As the antioxidant enzyme Superoxide dismutase needs zinc and other minerals to function, zinc requirements are greatly increased.  A few years ago, Aaseth, Haugen and Forre found that supplementation with zinc and other minerals (copper and selenium) could reduce joint inflammation.  Essential fatty acids are also helpful in RA and I will be devoting another newsletter to them later in the year.

Other conditions:

There is some evidence that diabetics can be helped by zinc supplementation (mainly because there is an increased loss of it in the urine) together with vitamin C, chromium and essential fatty acids.

One symptom of zinc deficiency is poor sense of taste or smell and this has been suggested as a possible factor in Anorexia nervosa.  While the initial cause is likely to be psychological rather than physical, anorexics are likely to become mineral deficient so it may perpetuate the illness once it is established; see Shay and Mangian.             top of page

Zinc supplementation:

The recommended supplementation rate for zinc is 5-25 milligrams per day for adults; not more than 15 mg per day for children.  However, the only completely reliable way to determine zinc deficiency is measurement of blood levels, so if one is taking nutritional supplements without the supervision of a doctor or nutritional therapist, a multi-mineral supplement is preferable.  This is not only because one cannot be certain that one actually is deficient in zinc, but because high levels of supplementation with one mineral may interfere with absorption of another.  For example, excess iron interferes with absorption of zinc and excess zinc, in its turn can interfere with absorption of copper.

Multi-mineral preparations in the form of colloidal suspensions are becoming more popular as they are more efficiently absorbed by the body and are easier for those with digestive problems to take.  As colloidal suspensions are more efficiently absorbed, the dosage required is likely to be less than with tablets.

 J Nutr 2000 May;130(5S Suppl):1447S-54

R.K. Chandra, Janeway Child Health Centre, 1 Janeway Place, St John's,
Nfld. A1A 1R8; Canada.
Nutrition and the immune system: An introduction.
American Journal of Clinical Nutrition. Vol 66(2) (pp 460S-463S), 1997.
Abstract
Nutrition is a critical determinant of immune responses and malnutrition
the most common cause of immunodeficiency worldwide. Protein-energy
malnutrition is associated with a significant impairment of cell-mediated
immunity, phagocyte function, complement system, secretory immunoglobulin
A antibody concentrations, and cytokine production. Deficiency of single
nutrients also results in altered immune responses: this is observed even
when the deficiency state is relatively mild. Of the micronutrients, zinc;
selenium; iron; copper; vitamins A, C, E, and B-6; and folic acid have
important influences on immune responses. Overnutrition and obesity also
reduce immunity. Low-birth-weight infants have a prolonged impairment of
cell-mediated immunity that can be partly restored by providing extra
amounts of dietary zinc. In the elderly, impaired immunity can be enhanced
by modest amounts of a combination of micronutrients. These findings have
considerable practical and public health significance.         top of page

J Nutr 2000 May;130(5S Suppl):1424S-31S

Therapeutic application of zinc in human immunodeficiency virus against opportunistic infections.

Mocchegiani E, Muzzioli M.

Immunology Centre, Research Department, Italian National Research Centres on Aging, 60121 Ancona, Italy.

The relevance of zinc in resistance to infections by virus, fungi and bacteria is recognized because of its pivotal role in the efficiency of the entire immune system, in particular in conferring biological activity to a thymic hormone called thymulin, which has differentiation properties on T-cell lines. In infection with human immunodeficiency virus (HIV), the zinc-bound form of thymulin (active thymulin, ZnFTS) is strongly reduced in stage IV of the disease (Centers for Disease Control and Prevention classification) with concomitant decrements in CD4(+) cell count and zincemia values. The zinc-unbound form of thymulin (inactive thymulin, FTS) is, in contrast, very high. The in vitro addition of zinc to plasma samples induces a recovery of the thymulin active form, suggesting low zinc bioavailability as the cause of impaired thymic functions with consequent CD4(+) depletion. An analysis of risk factors for the incidence of recidivism opportunistic infections shows CD4(+) depletion and zinc deficiency to have significant scores. Supplementation with zinc for 1 mo (45 mg Zn(2+)/d) associated with zidovudine (AZT) therapy in stage IV induces recovery of active zinc-bound thymulin, of zincemia, of CD4(+) cells with concomitant reduction (50%) of recidivism opportunistic infections compared with the AZT-treated group. Complete disappearance of recidivism by Candida aesophagea or Pneumocystis carinii is observed after supplementation with zinc. The relative risk factors (CD4(+) depletion and zinc-deficiency) have lower scores in the HIV-positive zinc-treated group, confirming, as such, the relevance of zinc in opportunistic infections that involve extracellular matrix. Such an assumption is indirectly confirmed with new HAART, where no opportunistic infections occur. Indeed, HIV RNA is inversely correlated with both CD4(+) and zincemia values (r = -0.73, P<0.01) in HAART-treated subjects. Lower scores for the same relative factors for the appearance of opportunistic infections are present in HAART-treated subjects compared with those treated with AZT. These findings, on the one hand, show the poor efficacy of AZT therapy compared with HAART therapy for the progression of HIV, but on the other hand, they suggest that the lack of occurrence of opportunistic infections by HAART may also result from major zinc bioavailability. This further supports the key role played by zinc against opportunistic infections in HIV with a possible independent effect by either HIV or the pathogens involved.

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J Nutr 2000 May;130(5S Suppl):1493S-9S