Suppression

Zinc

Category: Natural chemicals

Type

Voluntary

Introduction and description

Zinc is a metallic chemical element with the symbol Zn. It is the 24th most abundant element in the Earth's crust. It is classified as an essential mineral of "exceptional biologic and public health importance". We will see why in a moment.

There are 2-4 grams of zinc distributed throughout the human body. Most zinc is in the brain, muscle, bones, kidney, and liver, with the highest concentrations in the prostate and parts of the eye. Semen is particularly rich in zinc, which is a key factor in prostate gland function and reproductive organ growth.

There is a vital balancing act that takes place between zinc, copper and iron in our blood. In blood plasma, zinc is bound to and transported by albumin (60%, low-affinity) and transferrin (10%). Since transferrin also transports iron, excessive iron reduces zinc absorption, and vice-versa. A similar reaction occurs with copper. The concentration of zinc in blood plasma stays relatively constant regardless of zinc intake.

Zinc may be held in the intestines or liver of animals in reserve. Metallothionein in intestinal cells is capable of adjusting absorption of zinc by 15–40%. However, inadequate or excessive zinc intake can be harmful; excess zinc particularly impairs copper absorption because metallothionein absorbs both metals.

Zinc is an essential trace element, necessary for plants, animals, and microorganisms. In the human body it is found in the following: 

  • Enzymes - Zinc is found in at least 100 specific enzymes. It is "typically the second most abundant transition metal in organisms" after iron and it is the only metal which appears in all enzyme classes.
     
  • Proteins - Zn ions are “often coordinated to the amino acid side chains of aspartic acid, glutamic acid, cysteine and histidine. The theoretical and computational description of this zinc binding in proteins (as well as that of other transition metals) is difficult”. So maybe better to say it is key to the existence and functioning of essential amino acids. A bit more “A 2006 study estimated that about 10% of human proteins (2800) potentially bind zinc, in addition to hundreds which transport and traffic zinc” [trafficking in zinc – what a wonderful thought]
     
  • Genes – Zinc has roles in “the metabolism of RNA and DNA, signal transduction, and gene expression”. Zinc serves a structural role in 'zinc fingers'. Zinc fingers form parts of some transcription factors, which are proteins that recognize DNA base sequences during the replication and transcription of DNA.

Role of zinc

Not only are we made of zinc as we have seen above, but zinc is essential in a large number of our functions - digestion, respiration, and of key importance in the immune system.  For example: 

  • Respiration [and digestion] - Two examples of zinc-containing enzymes are carbonic anhydrase and carboxypeptidase, which are vital to the processes of carbon dioxide (CO2) regulation and digestion of proteins, respectively.
    In vertebrate blood, carbonic anhydrase converts CO2 into bicarbonate and the same enzyme transforms the bicarbonate back into CO2 for exhalation through the lungs. Without this enzyme, this conversion would occur about one million times slower at the normal blood pH of 7 or would require a pH of 10 or more. So, crudely put, breathlessness can be caused by zinc deficiency
     
  • Cell death regulation – Zinc regulates apoptosis. Apoptosis is the process of programmed cell death - in effect planned death and rejuvenation of cells. As old cells die they are replaced by new ones, hence in some senses zinc controls 'aging', but only in the sense that if old worn out cells don't die we get no new ones. Of course all the Americans keen on looking 20 when they are 90 have latched on to this, but there are far more important aspects to this effect. The Age-Related Eye Disease Study, for example, determined that zinc is the treatment for age-related macular degeneration.
     
  • Inter cell communication - Cells in the salivary gland, prostate, immune system and intestine use zinc signaling as one way to communicate with other cells.
     
  • Immune system – zinc appears to be key in the functioning of our immune system. All the claimed benefits for zinc as an anti-viral agent, an anti-bacterial agent, an anti-fungal agent and an anti-parasitic agent are actually due to the fact it supports our immune system in fighting all these. The immune system is the means of defence, zinc plays a key part in fuelling the system.

Zn deficiency can have marked effects on virtually all components of the immune system. That these effects can be functionally significant is demonstrated by the increased susceptibility of Zn-deficient animals to a number of bacterial, viral, and parasitic challenges. In addition, strong epidemiological data support the belief that Zn deficiency is a major factor underlying immune dysfunction in select human populations. Despite recognition of the importance of Zn in the ontogeny and functioning of the immune system, the biochemistry underlying the effects of Zn on immune response are not well understood. Future efforts to delineate the effects of Zn on the production, release, and action of cytokines will likely produce significant advances in our understanding of the influence of this element on the immune system. The recent observation that Zn may be critical for the activity and binding of protein kinase C in lymphocyte membranes suggests that another fruitful area of research will involve examination of the influence of Zn on lymphocyte membrane structure and function. Finally, the recent recognition that Zn may be a critical factor in the activation/inactivation of immunoregulatory genes provides us with yet another avenue of research.  PMID: 2200472

Some history

The value of zinc in promoting health has been known for thousands and thousands of years. The oldest known pills, made of the zinc carbonates hydrozincite and smithsonite, were used for sore eyes, and were found aboard the roman ship Relitto del Pozzino, which wrecked in 140 BC.

Indian medicine has also incorporated zinc. The Rasaratna Samuccaya, for example, written in approximately the 13th century AD, mentions two types of zinc-containing ores; one used for metal extraction and another used for medicinal purposes. Zinc was distinctly recognized as a metal under the designation of Yasada or Jasada in the medical Lexicon ascribed to the Hindu king Madanapala and written about the year 1374.

These days, zinc is used in some unusual applications. Zinc lactate, for example, is used in toothpaste to prevent halitosis. Zinc pyrithione is widely applied in shampoos because of its anti-dandruff function.

When we were young [60 years ago], the three medications most frequently used by our Mums was calamine lotion, zinc and castor oil ointment and zinc lozenges.

  • Calamine lotion containing zinc was used as an anti-itching agent, and to treat sunburn, eczema, rashes, chickenpox rash, and insect bites and stings. Very effective it was too, although it dried out the skin, even though it was quite cooling and soothing. I assume the drying effect also helped in its other uses to treat weeping or oozing blisters and acne abscesses.
  • Zinc and castor oil ointment was used in a similar way but where a cream was needed rather than a drying lotion. That worked too. It was often used to prevent nappy rash.
  • Finally the zinc lozenges were used for the common cold in an attempt to shorten the duration of colds. And low and behold, a recent study has found that “trials which used zinc acetate lozenges found an average 42% reduction in the duration of colds”.

Mums know best.

Diseases and illnesses resulting from zinc imbalance

Zinc imbalance can be of both deficiency and overdose.  Zinc deficiency affects about two billion people in the developing world and is associated with many diseases. In children it causes growth retardation, delayed sexual maturation, infection susceptibility, and diarrhoea, contributing to the death of about 800,000 children worldwide per year. Consumption of excess zinc can cause ataxia, lethargy and copper deficiency.  More details can be found by following the link to the overload section. 

Food sources

In the U.S., the Recommended Dietary Allowance (RDA) is 8 mg/day for women and 11 mg/day for men, but this is a little meaningless unless you know what your actual levels are and whether you are deficient or overloaded! We should be able to get most of our zinc from food and a list follows, however, a word of warning is needed here about plants as a source of zinc.

The concentration of zinc in plants varies based on levels of the element in soil. Zinc deficiency is crop plants' most common micronutrient deficiency; it is particularly common in high-pH soils. Zinc-deficient soil is cultivated in the cropland of about half of Turkey and India, a third of China, and most of Western Australia. Plants that grow in soils that are zinc-deficient are more susceptible to disease, just like us.

The following list was derived from the USDA Nutrients database 

  • Oysters - top of the list for content see fish and shellfish below
  • Seeds – cotton, sesame, pumpkin, poppy, celery, mustard, caraway, sunflower, dill, safflower, chia, flax, fennel
  • Wholegrains
  • Red meat – beef, lamb, veal, pork, ostrich, geese, duck 
  • Offal - liver, heart, giblets
  • Game
  • Herbs – chervil, basil, thyme, parsley, chives, coriander, sage, tarragon, bay leaf, marjoram, dill, rosemary
  • Marmite and vegemite
  • Egg yolk
  • Fish and shellfish – crab, lobster, cuttlefish, octopus, whelk
  • Mushrooms – shiitake,
  • Spices – cardamon, anise, cumin, turmeric, paprika, ginger
  • Chocolate
  • Nuts – peanuts, pine nuts, cashew, pecans, hickory, brazil, walnuts, almonds, butternuts
  • Peanut butter
  • Maple syrup
  • Beans – adzuki, soy beans, lentils, white, chickpeas, broad, kidney
  • Cheese – cheddar, 'swiss', mozarella, gouda, gruyere, parmesan,
  • Popcorn
  • Turkey, chicken

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