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Zinc.



KEY POINTS

* Zinc is an essential nutrient, required for numerous metabolic functions, including gene expression, growth and immunity.

* Manifestations of zinc deficiency zinc deficiency (zinkˑ d·fiˑ ·sh  include growth retardation, high rates of infection, skin lesions Skin Lesions Definition

A skin lesion is a superficial growth or patch of the skin that does not resemble the area surrounding it.
Description

Skin lesions can be grouped into two categories: primary and secondary.
 and impaired wound healing wound healing Physiology The repair of a wound Steps Inflammation, repair and closure, remodeling, final healing; repair of incisions may be either simple–'clean' wounds with little loss of tissue heal by 'primary intention', or 'dirty' wounds heal by .

* Zinc deficiency is a major contributor to the burden of disease in developing countries.

* Seafood and red meat are good sources of bioavailable zinc. Dietary zinc from plant sources is less bioavailable due to the interaction with phytate.

* The recommended dietary intake for zinc is 8 and 14 mg/day for women and men, respectively The Dietary Guidelines dietary guidelines Cardiology A series of dietary recommendations from the Nutrition Committee of the Am Heart Assn, that promote cardiovascular health. See Caloric restriction, food pyramid, French paradox.  for Australian Adults identify red meat as a substantial source of zinc.

INTRODUCTION

Zinc is involved in a number of metabolic processes, including protein and nucleic acid synthesis, and for the synthesis and action of insulin. It is the most common catalytic metal ion in the cytoplasm cytoplasm: see protoplasm.
cytoplasm

Portion of a eukaryotic cell outside the nucleus. The cytoplasm contains all the organelles (see eukaryote).
 of cells. Carbonic anhydrase was the first discovered zinc metalloenzyme; other enzymes include: carboxypeptidase carboxypeptidase /car·boxy·pep·ti·dase/ (-pep´ti-das) any exopeptidase that catalyzes the hydrolytic cleavage of the terminal or penultimate bond at the end of a peptide or polypeptide where the free carboxyl group occurs. , alkaline phosphatase, DNA/RNA polymerase and superoxide dismutase. (1-3) As a component of enzymes, known as metalloenzymes, zinc participates in the reaction at the active site or provides structural integrity to the enzyme. Genes such as those involved in the regulation of redox redox (rē`dŏks): see oxidation and reduction.  state, fatty acid metabolism Fatty acids are an important source of energy for many organisms. Excess glucose can be stored efficiently as fat. Triglycerides yield more than twice as much energy for the same mass as do carbohydrates or proteins. , signal transduction and platelet activation have been recognised as potential candidates for regulation by zinc: some genes are positively affected, and others negatively; whereas some are affected only by extremes of zinc status. Zinc-containing proteins in the human genome, known as 'zinc fingers', are able to interact with DNA DNA: see nucleic acid.
DNA
 or deoxyribonucleic acid

One of two types of nucleic acid (the other is RNA); a complex organic compound found in all living cells and many viruses. It is the chemical substance of genes.
 and act as transcriptional mediators. (1,2) Zinc serves as a structural component that allows for the coordinate binding of amino acids, mainly cysteine cysteine (sĭs`tēn), organic compound, one of the 20 amino acids commonly found in animal proteins. Only the l-stereoisomer participates in the biosynthesis of mammalian protein.  and histidine histidine (hĭs`tĭdēn), organic compound, one of the 22 α-amino acids commonly found in animal proteins. Only the l-stereoisomer appears in mammalian protein.  residues in the protein chain, to form a finger-like structure.

Adult humans contain 1.5-2.5 g of zinc, which is distributed in all tissues but mostly in fat-free mass such as bones and muscles. Dietary zinc is absorbed mainly from the duodenum duodenum: see intestine; pancreas.
duodenum

First and shortest (9–11 in., or 23–28 cm) segment of the small intestine. It curves down and then up from the pylorus of the stomach, where chyme enters it.
 by active and passive mechanisms. Once absorbed, zinc is transported to the liver bound to albumin. The major route of zinc excretion is by the intestine, followed by the kidneys. Smaller amounts of zinc are shed in skin cells or secreted by the prostate gland. (1-3) With this background, this paper discusses zinc deficiency, reviews food sources of zinc, and comments on the role of red meat in providing zinc in the overall diet.

ZINC DEFICIENCY

A number of conditions predispose pre·dis·pose
v.
To make susceptible, as to a disease.
 to zinc deficiency and are related to: decreased intake; decreased absorption; decreased utilisation secondary to other conditions, such as alcoholism; increased losses in conditions such as diarrhoea and excessive vomiting; and increased requirement associated with growth, pregnancy and lactation lactation

Production of milk by female mammals after giving birth. The milk is discharged by the mammary glands in the breasts. Hormones triggered by delivery of the placenta and by nursing stimulate milk production.
. (1-3) Zinc deficiency was first observed in Iran and Egypt during the 1960s. (3) The first case of severe zinc deficiency was a 21-year-old man who resembled a 10-year-old boy. He displayed symptoms that included growth retardation, hypogonadism Hypogonadism Definition

Hypogonadism is the condition more prevalent in males in which the production of sex hormones and germ cells are inadequate.
 and delayed sexual maturation. Other manifestations of zinc deficiency reported subsequently include high rates of infection (e.g. pneumonia) and diarrhoea due to an immune deficiency, diverse forms of skin lesions (e.g. eczema and alopecia alopecia (ăl'əpē`shēə): see baldness. ), impaired wound healing, loss of taste, and night blindness. (1,2)

The World Health Organisation (WHO) considers zinc deficiency to be a major contributor to the burden of disease in developing countries, especially in those with a high mortality rate. (4) The combination of low zinc intake, usually from sources with poor bioavailability bioavailability /bio·avail·a·bil·i·ty/ (bi?o-ah-val?ah-bil´i-te) the degree to which a drug or other substance becomes available to the target tissue after administration.

bi·o·a·vail·a·bil·i·ty
n.
, and an increased requirement for zinc, for example in children, predisposes to zinc deficiency The International Zinc Nutrition Consultative Group (IZiNCG) has provided estimates of the risk of zinc deficiency in 176 countries based on data from the Food and Agricultural Organisation's food balance sheets. (5) Bioavailable zinc is calculated and compared with the estimated average requirement estimated average requirement (E.A.R.),
n the accepted standard level of nutrients that an average person requires. The basis for the Recommended Daily Allowance is established by the U.S. government.
. Based on these estimates, it appears that 25% of the populations of South and South-East Asia and Latin America are at risk of inadequate zinc intake, compared with 10% of the population of Western Europe and North America. Data on a selected number of countries are shown in Table 1.

Assessing zinc status is hindered by the absence of reliable biomarkers; however, as a step towards estimating the global prevalence of zinc deficiency, IZiNCG has suggested the use of stunting prevalence (height-for-age below the expected range) as it is the best known and easiest to measure of the symptoms of zinc deficiency. IZiNCG has also suggested the use of data on the rates of iron-deficiency anaemia anaemia

see anemia.
 as a crude indicator of zinc deficiency, because iron and zinc are often found in the same foods and both nutrients have similar obstacles to their bioavailability. (5)

FOOD SOURCES OF ZINC

Zinc is found widely in the food supply, but its bioavailability from different foods is highly variable. Rich sources of zinc include: oysters, red meat, liver and cheese. Zinc in animal products, crustacea and mollusks is more readily absorbed than from plant foods. Cereal grains, legumes Legumes
A family of plants that bear edible seeds in pods, including beans and peas.

Mentioned in: Cholesterol, High

legumes (l
 and nuts are rich in phytate (the main storage form of phosphorous phos·pho·rous
adj.
Of, relating to, or containing phosphorus, especially with a valence of 3 or a valence lower than that of a comparable phosphoric compound.
 in plants), which bind zinc in the intestine and reduce its absorption. (6) The early cases of zinc deficiency were associated with high phytate-containing foods: unleavened bread from unrefined wheat flour as a dietary staple, and beans. (3) The molar ratio of phytate to zinc in the diet has been proposed as a predictor of zinc bioavailability, and ratios greater than 15 have been associated with suboptimal Suboptimal
A solution is called suboptimal if a part of the solution has been optimized without regards to the overall objective.
 zinc status. Three categories of bioavailability (Table 2) have been put forward by the WHO. (7)

To minimise the risk of zinc deficiency, it has been suggested that dietary diversification is required, including the increase in consumption of foods from animal sources and the introduction of food processing techniques, such as fermentation, that will reduce the zinc-chelating potency of phytate. (5,8,9) The WHO proposed the use of zinc supplementation or fortification fortification, system of defense structures for protection from enemy attacks. Fortification developed along two general lines: permanent sites built in peacetime, and emplacements and obstacles hastily constructed in the field in time of war.  of complementary foods given to breastfed infants starting at six months of age as a means of meeting their requirement for zinc. It has been argued, however, that the inclusion of meat in complementary feeding in developed and developing countries will meet zinc requirements and alleviate the need for supplementation. (10) In Kenyan children aged 6-14 years, the introduction of a meat-based snack over a two-year intervention resulted in increased growth and higher cognitive scores compared with children who consumed a milk- or fat-based snack. (11) Such strategies will have the advantage of improving not only the dietary content and bioavailability of zinc, but also those of other nutrients, such vitamin B12 and iron.

The concentration of zinc in plasma is the most commonly used diagnostic indicator of zinc status. However, zinc in this compartment represents less than 1% of the body pool of zinc, and hence, its measurement provides limited information about the zinc status of the individual. (1) Unlike many other micronutrients This is a list of micronutrients.

Vitamins
  • Vitamin A (retinol)
  • Vitamin B complex
  • Vitamin B1 (thiamin)
  • Vitamin B2 (riboflavin)
, a sensitive biomarker of zinc status is yet to be identified.

Australian dietary surveys have identified low zinc intakes in preschool children and adolescents, (12,13) but biochemical screening of preschool children across a range of socioeconomic status showed that plasma zinc concentrations were within the normal range. (14) Vegetarian men and women were shown to have lower zinc intakes than omnivores. (15) The median intake of zinc in vegetarian female individuals was reported to be 5.8 mg/day, equivalent to 70% of the recommended dietary intake (RDI RDI - Receiver Data Interface ), and likely to be derived from sources with low bioavailability. Nevertheless, no clear differences in plasma zinc concentrations were observed. In the elderly, particularly in institutionalised Adj. 1. institutionalised - officially placed in or committed to a specialized institution; "had hopes of rehabilitating the institutionalized juvenile delinquents"
institutionalized

2.
 individuals, zinc status is often compromised. (16) A recent study of aged-care residents showed that plasma zinc concentrations were below the normal range in 46% of subjects, and that these individuals had lower functional mobility scores ('Timed Up and Go' test) than those with plasma zinc concentrations in the normal range. (17) Zinc deficiency has been reported in Australian Indigenous children. (18) Zinc supplementation, however, has not been shown to be effective in increasing linear growth (19) or recovery from acute diarrhoea. (20) In these circumstances, the data are suggestive of an underlying confounding factor such as parasitic infection.

RED MEAT AS A SOURCE OF ZINC IN THE AUSTRALIAN DIET

The Australian National Nutrition Survey in 1995 (21,22) estimated the mean intakes of zinc in male and female individuals to be 14.4 and 9.7 mg/day, respectively. A considerable proportion of men in the age range of 25-64 years were consuming zinc at levels below the RDI (14 mg/day), and men aged >65 years were consuming zinc levels that were consistently below the RDI. A smaller percentage of women than men were consuming zinc levels below the RDI (8 mg/day) (Table 3).

The National Nutrition Survey results showed that the category of 'meat, poultry and game products and dishes' provided 32% and 39% of the zinc in the diet of adult female and male individuals, respectively. (22) Muscle meat was a major source of zinc for adolescents (contributing 14% of the total intake of zinc) and adults (15%), and a moderate source for children (9%). Moderate sources of zinc intake for all people aged two years and older were dairy milk, breads, and mixed dishes where beef, veal or cereals is the major ingredient. The proportion of the population recording low zinc intakes in the survey was inversely related to the consumption of red meat on the day of the survey. (23)

The Dietary Guidelines for Australian Adults (DGAA DGAA Dumfries and Galloway Arts Association ) encourage individuals to 'include lean meat, fish, poultry and/or alternatives'. The DGAA state that red meats (defined as muscle meat from cattle, sheep, goat and kangaroo) provide substantial amounts of zinc. (24) The RDI for zinc is 14 mg/day for men and 8 mg/day for women, with an additional 2-3 mg for pregnancy and 3-4 mg per day for lactation. (25) The current RDI for women is a third lower than the previous Australian RDI. The new figure for men is slightly higher. The upper limit of intake is 40 mg/day.

CONCLUSIONS

Zinc is an essential nutrient, required for numerous metabolic functions, and its deficiency results in growth retardation, high rates of infection, skin lesions and impaired wound healing. Zinc deficiency is a major contributor to the burden of disease in developing countries. Seafood and red meat are good sources of bioavailable zinc. Dietary zinc from plant sources is less bioavailable due to the interaction with phytate.

REFERENCES

1 Samman S. Zinc. In: Mann JI, Truswell AS, eds. Essentials of Human Nutrition, 3rd edn. Oxford: Oxford University Press, 2007; 138-42.

2 King JC, Cousins RJ. Zinc. In: Shike M, Ross AC, Caballero cab·al·le·ro  
n. pl. cab·al·le·ros
1. A Spanish gentleman; a cavalier.

2. A man who is skilled in riding and managing horses; a horseman.
 B, Cousins RJ, eds. Modern Nutrition in Health and Disease, 10th edn. Philadelphia, PA: Lippincott, Williams & Wilkins, 2006; 271-85.

3 Prasad Prasāda (Sanskrit: प्रसाद), prasād/prashad (Hindi), Prasāda in (Kannada), prasādam (Tamil), or prasadam  AS. Discovery and importance of zinc in human nutrition. Fed Proc 1984; 43: 2829-34.

4 World Health Organisation. The World Health Report 2002: Reducing Risks, Promoting Healthy Lifestyles. Geneva Geneva, canton and city, Switzerland
Geneva (jənē`və), Fr. Genève, canton (1990 pop. 373,019), 109 sq mi (282 sq km), SW Switzerland, surrounding the southwest tip of the Lake of Geneva.
: WHO; 2002.

5 International Zinc Nutrition Consultative Group (IZiNCG). Technical document #1. Assessment of the risk of zinc deficiency in populations and options for its control. Food Nutr Bull 2004; 25 (Suppl. 2): S95-203.

6 Sandstrom B. Bioavailability of zinc. Eur J Clin Nutr 1997; 51 (Suppl. 1): S17-19.

7 World Health Organisation. Trace Elements in Human Nutrition and Health. Geneva: WHO, 1996.

8 Shrimpton R, Gross R, Damton-Hill I, Young M. Zinc deficiency: what are the most appropriate interventions? Br Med J 2005; 330:347-9.

9 Gibson RS. Zinc: the missing link in combating micronutrient mi·cro·nu·tri·ent
n.
A substance, such as a vitamin or mineral, that is essential in minute amounts for the proper growth and metabolism of a living organism.
 malnutrition in developing countries. Proc Nutr Soc 2006; 65: 51-60.

10 Krebs NF, Hambidge KM. Complementary feeding: clinically relevant factors affecting timing and composition. Am J Clin Nutr 2007; 85: 639S-45S.

11 Neumann CG, Murphy SP, Gewa C, Grillenberger M, Bwibo NO. Meat supplementation improves growth, cognitive, and behavioral outcomes in Kenyan children. J Nutr 2007; 137: 1119-23.

12 Magarey A, Boulton J. The Adelaide Nutrition Study 2. Macronutrient macronutrient /mac·ro·nu·tri·ent/ (-noo´tre-ent) an essential nutrient required in relatively large amounts, such as carbohydrates, fats, proteins, or water; sometimes certain minerals are included, such as calcium, chloride, or sodium.  and micronutrient intakes at ages 11, 13 and 15 years: age and sex differences. Aust J Nutr Diet 1994; 51: 111-19.

13 Landers MCG, Warden RA, Hunt KA, Boulton TJC TJC Tyler Junior College (Texas)
TJC The Joint Commission (Oakbrook Terrace, IL)
TJC Temasek Junior College (Singapore)
TJC The Jockey Club
TJC True Jesus Church
. Nutrition in long day child care centres: are the guidelines realistic? Aust J Nutr Diet 1994; 51: 186-90.

14 Karr M, Mira M, Causer J et al. Plasma and serum micronutrient concentrations in preschool children. Acta Paediatr 1997; 86: 677-82.

15 Ball MJ, Ackland ML. Zinc intake and status in Australian vegetarians. Br J Nutr 2000; 83: 27-33.

16 Flint DM, Wahlqvist ML, Smith TJ, Parish AE. Zinc and protein status in the elderly. J Hum Nutr 1981; 35: 287-95.

17 Grieger J, Nowson C, Ackland ML. Anthropometric an·thro·pom·e·try  
n.
The study of human body measurement for use in anthropological classification and comparison.



an
 and biochemical markers for nutritional risk among residents within an Australian residential care facility. Asia Pac J Cin Nutr 2007; 16: 178-86.

18 Cheek DB, Spargo RM, Holt AB. Evidence for zinc deficiency in aboriginal settlements in Northwestern Australia. Med J Aust 1981; 1 (2 Suppl.): 4-5.

19 Smith RM, King RA, Spargo RM, Cheek DB, Field JB, Veitch LG. Growth-retarded aboriginal children with low plasma zinc levels do not show a growth response to supplementary zinc Lancet 1985; 8434: 923-4.

20 Valery PC, Torzillo PJ, Boyce NC et al. Zinc and vitamin A supplementation in Australian Indigenous children with acute diarrhoea: a randomised Adj. 1. randomised - set up or distributed in a deliberately random way
randomized

irregular - contrary to rule or accepted order or general practice; "irregular hiring practices"
 controlled trial. Med J Aust 2005; 182: 530-35.

21 Australian Bureau of Statistics The Australian Bureau of Statistics (ABS) is the Australian government agency that collects and publishes statistical information about Australia and its people. Population and Housing
The agency undertakes the Australian Census of Population and Housing.
. National Nutrition Survey. Selected Highlights Australia 1995. Canberra: Commonwealth of Australia Commonwealth of Australia: see Australia. , 1998.

22 Australian Bureau of Statistics. National Nutrition Survey. Nutrient Intakes and Physical Measurements Australia 1995. Canberra: Commonwealth of Australia, 1998.

23 Baghurst K, Record S, Leppards P. Red meat consumption in Australia: intakes, nutrient composition and changes over time. Aust J Nutr Diet 2000; 57: S3-36.

24 Commonwealth Department of Health and Ageing Health and Ageing is a research programme set up by the Geneva Association, also known as the International Association for the Study of Insurance Economics. The Geneva Association Research Programme on Health and Ageing seeks to bring together facts, figures and analyses . Dietary Guidelines for Australian Adults. A Guide to Healthy Eating. Canberra: Commonwealth of Australia, 2003.

25 Department of Health and Ageing. Nutrient Reference Values for Australia and New Zealand. Executive Summary. Canberra: Commonwealth of Australia, 2006.

Samir SAMMAN

Human Nutrition Unit, University of Sydney The University of Sydney, established in Sydney in 1850, is the oldest university in Australia. It is a member of Australia's "Group of Eight" Australian universities that are highly ranked in terms of their research performance. , Sydney, New South Wales New South Wales, state (1991 pop. 5,164,549), 309,443 sq mi (801,457 sq km), SE Australia. It is bounded on the E by the Pacific Ocean. Sydney is the capital. The other principal urban centers are Newcastle, Wagga Wagga, Lismore, Wollongong, and Broken Hill. , Australia
Table 1 Daily mean amounts of zinc, dietary phytate: zinc molar ratio, %
energy from animal foods and the risk of zinc deficiency in selected
countries (5)

                                                          Zinc
             Zinc intake  Phytate : zinc  % energy from   deficiency
Country      (mg/day)     molar ratio     animal sources  risk category

Cameroon      9.0         25.6             5.8            High
Gambia        8.1         26.9             5.3            High
Indonesia    10.0         28.4             4.4            High
Philippines   7.8         17.1            14.0            High
Vietnam       9.2         21.6             9.5            High
China        12.4         16.4            16.5            Medium
Croatia       7.9         13.5            20.6            Medium
Japan        11.0         15.8            21.1            Medium
Korea        11.9         18.0            13.8            Medium
Malaysia     10.3         14.7            20.2            Medium
Australia    13.3          6.9            32.9            Low
Italy        12.5          8.8            26.1            Low
UK           12.1          8.6            31.6            Low
USA          12.7         10.6            27.8            Low

Table 2 Dietary determinants of zinc bioavailability (7)

Estimated absorption  Type of diet

Low                   * Diet high in unrefined cereal grain
                      * High-phytate soya-protein products as the
                        primary protein source
                      * Phytate : zinc molar ratio >15
                      * Calcium >1 g/day
Moderate              * Mixed diet containing animal or fish protein
                      * Lacto-ovo, ovovegetarian or vegan diets that are
                        not based on unrefined cereals
                      * Phytate : zinc molar ratio <10
                      * Bioavailability of zinc is improved if the diet
                        includes animal protein sources
High                  * Refined diets, low in cereal fibre
                      * Phytate : zinc molar ratio <5
                      * Dietary protein primarily from animal foods

Table 3 Percentile distribution of daily zinc intake in Australian
adults (22)

                                                   Percentile
Group (RDI)                               10    25    50    75    90

All male individuals aged >19 years       10.8  12.4  14.0  15.9  18.1
  (14 mg)
Male individuals aged >65 years (14 mg)    9.2   9.9  11.0  12.3  13.9
All female individuals aged >19 years      7.4   8.3   9.3  10.6  12.5
  (8 mg)
Female individuals aged >65 years (8 mg)   7.3   7.9   8.6   9.5  10.7

The data are adjusted for within-person variation.
RDI = recommended dietary intake.
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Title Annotation:Section 2: Key nutrients delivered by red meat in the diet
Author:Samman, Samir
Publication:Nutrition & Dietetics: The Journal of the Dietitians Association of Australia
Date:Sep 1, 2007
Words:2680
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