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Zinc deficiency is defined either as insufficient
zinc Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...
to meet the needs of the body, or as a serum
zinc Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...
level below the normal range. However, since a decrease in the serum concentration is only detectable after long-term or severe depletion, serum zinc is not a reliable
biomarker In biomedical contexts, a biomarker, or biological marker, is a measurable indicator of some biological state or condition. Biomarkers are often measured and evaluated using blood, urine, or soft tissues to examine normal biological processes, p ...
for zinc status. Common symptoms include increased rates of diarrhea. Zinc deficiency affects the skin and gastrointestinal tract; brain and central nervous system, immune, skeletal, and reproductive systems. Zinc deficiency in humans is caused by reduced dietary intake, inadequate absorption, increased loss, or increased body system use. The most common cause is reduced dietary intake. In the U.S., the
Recommended Dietary Allowance The Dietary Reference Intake (DRI) is a system of nutrition recommendations from the National Academy of Medicine (NAM) of the National Academies (United States). It was introduced in 1997 in order to broaden the existing guidelines known as Rec ...
(RDA) is 8 mg/day for women and 11 mg/day for men."Zinc"
, pp. 442–501 in ''Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc''. National Academy Press. 2001.
The highest concentration of dietary zinc is found in
oyster Oyster is the common name for a number of different families of salt-water bivalve molluscs that live in marine or brackish habitats. In some species, the valves are highly calcified, and many are somewhat irregular in shape. Many, but not ...
s,
meat Meat is animal flesh that is eaten as food. Humans have hunted, farmed, and scavenged animals for meat since prehistoric times. The establishment of settlements in the Neolithic Revolution allowed the domestication of animals such as chic ...
,
bean A bean is the seed of several plants in the family Fabaceae, which are used as vegetables for human or animal food. They can be cooked in many different ways, including boiling, frying, and baking, and are used in many traditional dishes th ...
s, and nuts. Increasing the amount of zinc in the soil and thus in crops and animals is an effective preventive measure. Zinc deficiency may affect up to 2 billion people worldwide.


Signs and symptoms


Skin, nails and hair

Zinc deficiency may manifest as
acne Acne, also known as ''acne vulgaris'', is a long-term skin condition that occurs when dead skin cells and oil from the skin clog hair follicles. Typical features of the condition include blackheads or whiteheads, pimples, oily skin, and ...
,
eczema Dermatitis is inflammation of the skin, typically characterized by itchiness, redness and a rash. In cases of short duration, there may be small blisters, while in long-term cases the skin may become thickened. The area of skin involved c ...
,
xerosis Xeroderma, xerosis or xerosis cutis, or simply dry skin, is a skin condition characterized by excessively dry skin. The medical term ''xeroderma'', meaning "dry skin", derives from modern Latin, ''xero-'' 'dry' + Greek ''derma'' 'skin'. In most ...
(dry, scaling skin),
seborrheic dermatitis Seborrhoeic dermatitis, sometimes inaccurately referred to as seborrhoea, is a long-term skin disorder. Symptoms include red, scaly, greasy, itchy, and inflamed skin. Areas of the skin rich in oil-producing glands are often affected including the ...
, or
alopecia Hair loss, also known as alopecia or baldness, refers to a loss of hair from part of the head or body. Typically at least the head is involved. The severity of hair loss can vary from a small area to the entire body. Inflammation or scar ...
(thin and sparse hair). It may also impair or possibly prevent wound healing.


Mouth

Zinc deficiency can manifest as non-specific
oral ulceration A mouth ulcer (aphtha) is an ulcer that occurs on the mucous membrane of the oral cavity. Mouth ulcers are very common, occurring in association with many diseases and by many different mechanisms, but usually there is no serious underlying cause ...
,
stomatitis Stomatitis is inflammation of the mouth and lips. It refers to any inflammatory process affecting the mucous membranes of the mouth and lips, with or without oral ulceration. In its widest meaning, stomatitis can have a multitude of different cau ...
, or white tongue coating. Rarely it can cause
angular cheilitis Angular cheilitis (AC) is inflammation of one or both corners of the mouth. Often the corners are red with skin breakdown and crusting. It can also be itchy or painful. The condition can last for days to years. Angular cheilitis is a type of ch ...
(sores at the corners of the mouth).


Vision, smell and taste

Severe zinc deficiency may disturb the sense of smell and
taste The gustatory system or sense of taste is the sensory system that is partially responsible for the perception of taste (flavor). Taste is the perception produced or stimulated when a substance in the mouth reacts chemically with taste receptor ...
.
Night blindness Nyctalopia (; ), also called night-blindness, is a condition making it difficult or impossible to see in relatively low light. It is a symptom of several eye diseases. Night blindness may exist from birth, or be caused by injury or malnutrition ...
may be a feature of severe zinc deficiency, although most reports of night blindness and abnormal dark adaptation in humans with zinc deficiency have occurred in combination with other nutritional deficiencies (e.g.
vitamin A Vitamin A is a fat-soluble vitamin and an essential nutrient for humans. It is a group of organic compounds that includes retinol, retinal (also known as retinaldehyde), retinoic acid, and several provitamin A carotenoids (most notably ...
).


Immune system

Impaired immune function in people with zinc deficiency can lead to the development of respiratory, gastrointestinal, or other infections, e.g., pneumonia.Penny M. Zinc Protects: The Role of Zinc in Child Health. 2004.
The levels of inflammatory cytokines (e.g.,
IL-1β Interleukin-1 beta (IL-1β) also known as leukocytic pyrogen, leukocytic endogenous mediator, mononuclear cell factor, lymphocyte activating factor and other names, is a cytokine protein that in humans is encoded by the ''IL1B'' gene."Catabolin ...
, IL-2, IL-6, and TNF-α) in blood plasma are affected by zinc deficiency and zinc supplementation produces a dose-dependent response in the level of these cytokines. During inflammation, there is an increased cellular demand for zinc and impaired zinc homeostasis from zinc deficiency is associated with chronic inflammation.


Diarrhea

Zinc deficiency contributes to an increased incidence and severity of diarrhea.


Appetite

Zinc deficiency may lead to loss of appetite.


Cognitive function and hedonic tone

Cognitive functions, such as learning and
hedonic tone Valence, or hedonic tone, is the affective quality referring to the intrinsic attractiveness/"good"-ness (positive valence) or averseness/"bad"-ness (negative valence) of an event, object, or situation. The term also characterizes and categori ...
, are impaired with zinc deficiency. Moderate and more severe zinc deficiencies are associated with behavioral abnormalities, such as irritability, lethargy, and depression (e.g., involving
anhedonia Anhedonia is a diverse array of deficits in hedonic function, including reduced motivation or ability to experience pleasure. While earlier definitions emphasized the inability to experience pleasure, anhedonia is currently used by researchers ...
). Zinc supplementation produces a rapid and dramatic improvement in hedonic tone (i.e., general level of happiness or pleasure) under these circumstances. Zinc supplementation has been reported to improve symptoms of ADHD and depression.


Psychological disorders

Low plasma zinc levels have been alleged to be associated with many psychological disorders. Schizophrenia has been linked to decreased brain zinc levels. Evidence suggests that zinc deficiency could play a role in depression. Zinc supplementation may be an effective treatment in major depression.


Growth

Zinc deficiency in children can cause delayed growth and has been claimed to be the cause of stunted growth in one third of the world's population.


During pregnancy

Zinc deficiency during pregnancy can negatively affect both the mother and fetus. Animal studies indicate that maternal zinc deficiency can upset both the sequencing and efficiency of the birth process. An increased incidence of difficult and prolonged labor, hemorrhage, uterine
dystocia Obstructed labour, also known as labour dystocia, is the baby not exiting the pelvis because it is physically block during childbirth although the uterus contracts normally. Complications for the baby include not getting enough oxygen which may ...
and
placental abruption Placental abruption is when the placenta separates early from the uterus, in other words separates before childbirth. It occurs most commonly around 25 weeks of pregnancy. Symptoms may include vaginal bleeding, lower abdominal pain, and dang ...
has been documented in zinc deficient animals. These effects may be mediated by the defective functioning of estrogen via the estrogen receptor, which contains a
zinc finger A zinc finger is a small protein structural motif that is characterized by the coordination of one or more zinc ions (Zn2+) in order to stabilize the fold. It was originally coined to describe the finger-like appearance of a hypothesized struct ...
protein. A review of pregnancy outcomes in women with acrodermatitis enteropathica, reported that out of every seven pregnancies, there was one abortion and two malfunctions, suggesting the human fetus is also susceptible to the teratogenic effects of severe zinc deficiency. However, a review on zinc supplementation trials during pregnancy did not report a significant effect of zinc supplementation on neonatal survival. Zinc deficiency can interfere with many metabolic processes when it occurs during infancy and childhood, a time of rapid growth and development when nutritional needs are high. Low maternal zinc status has been associated with less attention during the neonatal period and worse motor functioning. In some studies, supplementation has been associated with motor development in very low
birth weight Birth weight is the body weight of a baby at its birth. The average birth weight in babies of European descent is , with the normative range between . On average, babies of South Asian and Chinese descent weigh about . As far as low birth weigh ...
infants and more vigorous and functional activity in infants and toddlers.


Testosterone production

Zinc is required to produce testosterone. Thus, zinc deficiency can lead to reduced circulating testosterone, which could lead to sexual immaturity (Ananda Parsad, et al.)
hypogonadism Hypogonadism means diminished functional activity of the gonads—the testes or the ovaries—that may result in diminished production of sex hormones. Low androgen (e.g., testosterone) levels are referred to as hypoandrogenism and low estroge ...
, and delayed
puberty Puberty is the process of physical changes through which a child's body matures into an adult body capable of sexual reproduction. It is initiated by hormonal signals from the brain to the gonads: the ovaries in a girl, the testes in a ...
.


Causes


Dietary deficiency

Zinc deficiency can be caused by a diet high in phytate-containing whole grains, foods grown in zinc deficient soil, or processed foods containing little or no zinc. Conservative estimates suggest that 25% of the world's population is at risk of zinc deficiency. In the U.S., the
Recommended Dietary Allowance The Dietary Reference Intake (DRI) is a system of nutrition recommendations from the National Academy of Medicine (NAM) of the National Academies (United States). It was introduced in 1997 in order to broaden the existing guidelines known as Rec ...
(RDA) is 8 mg/day for women and 11 mg/day for men. RDA for pregnancy is 11 mg/day. RDA for lactation is 12 mg/day. For infants up to 12 months the RDA is 3 mg/day. For children ages 1–13 years the RDA increases with age from 3 to 8 mg/day. The following table summarizes most of the foods with significant quantities of zinc, listed in order of quantity per serving, unfortified. Note that all of the top 10 entries are meat, beans, or nuts. Recent research findings suggest that increasing atmospheric carbon dioxide concentrations will exacerbate zinc deficiency problems in populations that consume grains and legumes as
staple food A staple food, food staple, or simply a staple, is a food that is eaten often and in such quantities that it constitutes a dominant portion of a standard Diet (nutrition), diet for a given person or group of people, supplying a large fraction of ...
s. A
meta-analysis A meta-analysis is a statistical analysis that combines the results of multiple scientific studies. Meta-analyses can be performed when there are multiple scientific studies addressing the same question, with each individual study reporting m ...
of data from 143 studies comparing the nutrient content of grasses and legumes grown in ambient and elevated CO2 environments found that the edible portions of wheat, rice,
pea The pea is most commonly the small spherical seed or the seed-pod of the flowering plant species ''Pisum sativum''. Each pod contains several peas, which can be green or yellow. Botanically, pea pods are fruit, since they contain seeds and d ...
s and
soybean The soybean, soy bean, or soya bean (''Glycine max'') is a species of legume native to East Asia, widely grown for its edible bean, which has numerous uses. Traditional unfermented food uses of soybeans include soy milk, from which tofu ...
s grown in elevated CO2 contained less zinc and iron. Global atmospheric CO2 concentration is expected to reach 550 p.p.m. in the late 21st century. At this CO2 level the zinc content of these crops was 3.3 to 9.3% lower than that of crops grown in the present atmosphere. A model of the nutritional impact of these lower zinc quantities on the populations of 151 countries predicts that an additional 175 million people could face dietary zinc deficiency as the result of increasing atmospheric CO2.


Inadequate absorption

Acrodermatitis enteropathica is an inherited deficiency of the zinc carrier protein ZIP4 resulting in inadequate zinc absorption. It presents as growth retardation, severe diarrhea, hair loss, skin rash (most often around the genitalia and mouth) and opportunistic candidiasis and bacterial infections. Numerous small bowel diseases which cause destruction or malfunction of the gut mucosa enterocytes and generalized malabsorption are associated with zinc deficiency.


Increased loss

Exercising, high alcohol intake, and diarrhea all increase loss of zinc from the body. Changes in intestinal tract absorbability and permeability due, in part, to viral, protozoal, or bacteria pathogens may also encourage fecal losses of zinc.


Chronic disease

The mechanism of zinc deficiency in some diseases has not been well defined; it may be multifactorial.
Wilson's disease Wilson's disease is a genetic disorder in which excess copper builds up in the body. Symptoms are typically related to the brain and liver. Liver-related symptoms include vomiting, weakness, fluid build up in the abdomen, swelling of the legs, ...
, sickle cell disease, chronic kidney disease, chronic liver disease have all been associated with zinc deficiency. It can also occur after
bariatric surgery Bariatric surgery (or weight loss surgery) includes a variety of procedures performed on people who are obese. Long term weight loss through the standard of care procedures ( Roux en-Y bypass, sleeve gastrectomy, and biliopancreatic diversio ...
, mercury exposure and tartrazine. Although marginal zinc deficiency is often found in depression, low zinc levels could either be a cause or a consequence of mental disorders and their symptoms.


Mechanism

As biosystems are unable to store zinc, regular intake is necessary. Excessively low zinc intake can lead to zinc deficiency, which can negatively impact an individual's health. The mechanisms for the clinical manifestations of zinc deficiency are best appreciated by recognizing that zinc functions in the body in three areas: catalytic, structural, and regulatory. Zinc (Zn) is only common in its +2 oxidative state, where it typically coordinates with tetrahedral geometry. It is important in maintaining basic cellular functions such as
DNA replication In molecular biology, DNA replication is the biological process of producing two identical replicas of DNA from one original DNA molecule. DNA replication occurs in all living organisms acting as the most essential part for biological inheritan ...
,
RNA transcription Transcription is the process of copying a segment of DNA into RNA. The segments of DNA transcribed into RNA molecules that can encode proteins are said to produce messenger RNA (mRNA). Other segments of DNA are copied into RNA molecules called ...
,
cell division Cell division is the process by which a parent cell divides into two daughter cells. Cell division usually occurs as part of a larger cell cycle in which the cell grows and replicates its chromosome(s) before dividing. In eukaryotes, there ...
and cell activations. However, having too much or too little zinc can cause these functions to be compromised. Zinc is a critical component of the
catalytic Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
site of hundreds of kinds of different metalloenzymes in each human being. In its structural role, zinc coordinates with certain protein domains, facilitating protein folding and producing structures such as 'zinc fingers'. In its regulatory role, zinc is involved in the regulation of nucleoproteins and the activity of various inflammatory cells. For example, zinc regulates the expression of metallothionein, which has multiple functions, such as intracellular zinc compartmentalization and antioxidant function. Thus zinc deficiency results in disruption of hundreds of metabolic pathways, causing numerous clinical manifestations, including impaired growth and development, and disruption of reproductive and immune function. Pra1 (pH regulated antigen 1) is a
candida albicans ''Candida albicans'' is an opportunistic pathogenic yeast that is a common member of the human gut flora. It can also survive outside the human body. It is detected in the gastrointestinal tract and mouth in 40–60% of healthy adults. It is usu ...
protein that scavenges host zinc.


Diagnosis

Diagnosis is typically made based on clinical suspicion and a low level of zinc in the blood. Any level below 70 mcg/dl (normal 70-120 mcg/dl)is considered as zinc deficiency. Zinc deficiency could be also associated with low alkaline phosphatase since it acts a cofactor for this enzyme. There is a paucity of adequate zinc
biomarker In biomedical contexts, a biomarker, or biological marker, is a measurable indicator of some biological state or condition. Biomarkers are often measured and evaluated using blood, urine, or soft tissues to examine normal biological processes, p ...
s, and the most widely used indicator, plasma zinc, has poor
sensitivity and specificity ''Sensitivity'' and ''specificity'' mathematically describe the accuracy of a test which reports the presence or absence of a condition. Individuals for which the condition is satisfied are considered "positive" and those for which it is not are ...
.


Classification

Zinc deficiency can be classified as acute, as may occur during prolonged inappropriate zinc-free
total parenteral nutrition Parenteral nutrition (PN) is the feeding of nutritional products to a person intravenously, bypassing the usual process of eating and digestion. The products are made by pharmaceutical compounding companies. The person receives a nutritional mix ...
; or chronic, as may occur in dietary deficiency or inadequate absorption.


Prevention

Five interventional strategies can be used: * Adding zinc to soil, called agronomic biofortification, which both increases crop yields and provides more dietary zinc. * Adding zinc to food, called
food fortification Food fortification or enrichment is the process of adding micronutrients (essential trace elements and vitamins) to food. It can be carried out by food manufacturers, or by governments as a public health policy which aims to reduce the number of p ...
. The Republic of China, India, Mexico and about 20 other countries, mostly on the east coast of sub-Saharan Africa, fortify wheat flour and/or maize flour with zinc. * Adding zinc rich foods to diet. The foods with the highest concentration of zinc are proteins, especially animal meats, the highest being oysters. Per ounce, beef, pork, and lamb contain more zinc than fish. The dark meat of a chicken has more zinc than the light meat. Other good sources of zinc are nuts, whole grains, legumes, and yeast. Although whole grains and cereals are high in zinc, they also contain
chelating Chelation is a type of bonding of ions and molecules to metal ions. It involves the formation or presence of two or more separate coordinate bonds between a polydentate (multiple bonded) ligand and a single central metal atom. These ligands are ...
phytate Phytic acid is a six-fold dihydrogenphosphate ester of inositol (specifically, of the ''myo'' isomer), also called inositol hexakisphosphate (IP6) or inositol polyphosphate. At physiological pH, the phosphates are partially ionized, resulting in ...
s which bind zinc and reduce its bioavailability. * Oral repletion via tablets (e.g. zinc gluconate) or liquid (e.g. zinc acetate). Oral zinc supplementation in healthy infants more than six months old has been shown to reduce the duration of any subsequent diarrheal episodes by about 11 hours. * Oral repletion via multivitamin/mineral supplements containing zinc gluconate, sulfate, or acetate. It is not clear whether one form is better than another.


Epidemiology

Zinc deficiency affects about 2.2 billion people around the world. Severe zinc deficiency is rare, and is mainly seen in persons with acrodermatitis enteropathica, a severe defect in zinc absorption due to a congenital deficiency in the zinc carrier protein ZIP4 in the
enterocyte Enterocytes, or intestinal absorptive cells, are simple columnar epithelial cells which line the inner surface of the small and large intestines. A glycocalyx surface coat contains digestive enzymes. Microvilli on the apical surface increase i ...
. Mild zinc deficiency due to reduced dietary intake is common. Conservative estimates suggest that 25% of the world's population is at risk of zinc deficiency. Zinc deficiency is thought to be a leading cause of infant mortality. Providing micronutrients, including zinc, to humans is one of the four solutions to major global problems identified in the
Copenhagen Consensus Copenhagen Consensus is a project that seeks to establish priorities for advancing global welfare using methodologies based on the theory of welfare economics, using cost–benefit analysis. It was conceived and organized around 2004 by Bjørn Lo ...
from an international panel of economists.


History

Significant historical events related to zinc deficiency began in 1869 when zinc was first discovered to be essential to the growth of an organism ''
Aspergillus niger ''Aspergillus niger'' is a mold classified within the ''Nigri'' section of the ''Aspergillus'' genus. The ''Aspergillus'' genus consists of common molds found throughout the environment within soil and water, on vegetation, in fecal matter, on de ...
''. In 1929 Lutz measured zinc in numerous human tissues using the dithizone technique and estimated total body zinc in a 70 kg man to be 2.2 grams. Zinc was found to be essential to the growth of rats in 1933. In 1939
beriberi Thiamine deficiency is a medical condition of low levels of thiamine (Vitamin B1). A severe and chronic form is known as beriberi. The two main types in adults are wet beriberi and dry beriberi. Wet beriberi affects the cardiovascular system, r ...
patients in China were noted to have decreased zinc levels in skin and nails. In 1940 zinc levels in a series of autopsies found it to be present in all tissues examined. In 1942 a study showed most zinc excretion was via the feces. In 1950 a normal serum zinc level was first defined, and found to be 17.3–22.1 micromoles/liter. In 1956 cirrhotic patients were found to have low serum zinc levels. In 1963 zinc was determined to be essential to human growth, three enzymes requiring zinc as a cofactor were described, and a report was published of a 21-year-old Iranian man with stunted growth, infantile genitalia, and anemia which were all reversed by zinc supplementation. In 1972 fifteen Iranian rejected army inductees with symptoms of zinc deficiency were reported: all responded to zinc. In 1973 the first case of acrodermatitis enteropathica due to severe zinc deficiency was described. In 1974 the National Academy of Sciences declared zinc to be an essential element for humans and established a recommended daily allowance. In 1978 the Food and Drug Administration required zinc to be in total parenteral nutrition fluids. In the 1990s there was increasing attention on the role of zinc deficiency in childhood morbidity and mortality in developing countries. In 2002 the zinc transporter protein ZIP4 was first identified as the mechanism for absorption of zinc in the gut across the basolateral membrane of the enterocyte. By 2014 over 300 zinc containing enzymes have been identified, as well as over 1000 zinc containing transcription factors. Phytate was recognized as removing zinc from nutrients given to chicken and swine in 1960. That it can cause human zinc deficiency however was not recognized until Reinhold's work in Iran in the 1970s. This phenomenon is central to the high risk of zinc deficiency worldwide.


Soils and crops

Soil zinc is an essential micronutrient for crops. Almost half of the world's cereal crops are deficient in zinc, leading to poor crop yields. Many agricultural countries around the world are affected by zinc deficiency. In China, zinc deficiency occurs on around half of the agricultural soils, affecting mainly rice and maize. Areas with zinc deficient soils are often regions with widespread zinc deficiency in humans. A basic knowledge of the dynamics of zinc in soils, understanding of the uptake and transport of zinc in crops and characterizing the response of crops to zinc deficiency are essential steps in achieving sustainable solutions to the problem of zinc deficiency in crops and humans.


Biofortification

Soil and foliar application of zinc fertilizer can effectively increase grain zinc and reduce the phytate:zinc ratio in grain. People who eat bread prepared from zinc enriched wheat have a significant increase in serum zinc. Zinc fertilization not only increases zinc content in zinc deficient crops, it also increases crop yields. Balanced crop nutrition supplying all essential nutrients, including zinc, is a cost effective management strategy. Even with zinc-efficient varieties, zinc fertilizers are needed when the available zinc in the
topsoil Topsoil is the upper layer of soil. It has the highest concentration of organic matter and microorganisms and is where most of the Earth's biological soil activity occurs. Description Topsoil is composed of mineral particles and organic matt ...
becomes depleted. Plant breeding can improve zinc uptake capacity of plants under soil conditions with low chemical availability of zinc. Breeding can also improve zinc translocation which elevates zinc content in edible crop parts as opposed to the rest of the plant. Central Anatolia, in Turkey, was a region with zinc-deficient soils and widespread zinc deficiency in humans. In 1993, a research project found that yields could be increased by 6 to 8-fold and child nutrition dramatically increased through zinc fertilization. Zinc was added to fertilizers. While the product was initially made available at the same cost, the results were so convincing that Turkish farmers significantly increased the use of the zinc-fortified fertilizer (1 percent of zinc) within a few years, despite the repricing of the products to reflect the added value of the content. Nearly ten years after the identification of the zinc deficiency problem, the total amount of zinc-containing compound fertilizers produced and applied in Turkey reached a record level of 300,000 tonnes per annum. It is estimated that the economic benefits associated with the application of zinc fertilizers on zinc deficient soils in Turkey is around US$100 million per year. Zinc deficiency in children has been dramatically reduced.


References


Further reading

*


External links

* {{DEFAULTSORT:Zinc Deficiency Zinc Mineral deficiencies