Zinc deficiency

Skin, nails and hair

Zinc deficiency may manifest as acne,^[4] eczema, xerosis (dry, scaling skin), seborrheic dermatitis,^[5] or alopecia (thin and sparse hair).^[5][6] It may also impair or possibly prevent wound healing.^[6]

Mouth

Zinc deficiency can manifest as non-specific oral ulceration, stomatitis, or white tongue coating.^[5] Rarely it can cause angular cheilitis (sores at the corners of the mouth).^[7]

Vision, smell and taste

Severe zinc deficiency may disturb the sense of smell^[6] and taste.^{[8][9][10][11][12][13]} Night blindness may be a feature of severe zinc deficiency,^[6] 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).^[14]

Immune system

Impaired immune function in people with zinc deficiency can lead to the development of respiratory, gastrointestinal, or other infections, e.g., pneumonia.^[6][15][16] The levels of inflammatory cytokines (e.g., IL-1β, 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.^[17] During inflammation, there is an increased cellular demand for zinc and impaired zinc homeostasis from zinc deficiency is associated with chronic inflammation.^[17]

Diarrhea

Zinc deficiency contributes to an increased incidence and severity of diarrhea.^[15][16]

Appetite

Zinc deficiency may lead to loss of appetite.^[18]

Cognitive function and hedonic tone

Cognitive functions, such as learning and hedonic tone, are impaired with zinc deficiency.^[3][19] Moderate and more severe zinc deficiencies are associated with behavioral abnormalities, such as irritability, lethargy, and depression (e.g., involving anhedonia).^[20] Zinc supplementation produces a rapid and dramatic improvement in hedonic tone (i.e., general level of happiness or pleasure) under these circumstances.^[20] Zinc supplementation has been reported to improve symptoms of ADHD and depression.^[3][21][22]

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.^[23] Evidence suggests that zinc deficiency could play a role in depression.^[23][24][25] Zinc supplementation may be an effective treatment in major depression.^[26][27]

Growth

Zinc deficiency in children can cause delayed growth^[5] and has been claimed to be the cause of stunted growth in one third of the world's population.^[28]

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 and placental abruption has been documented in zinc deficient animals.^[29] These effects may be mediated by the defective functioning of estrogen via the estrogen receptor, which contains a zinc finger protein.^[29] 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.^[29]

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.^[30] Low maternal zinc status has been associated with less attention during the neonatal period and worse motor functioning.^[31] In some studies, supplementation has been associated with motor development in very low birth weight infants and more vigorous and functional activity in infants and toddlers.^[31]

Testosterone production

Zinc is required to produce testosterone. Thus, zinc deficiency can lead to reduced circulating testosterone, which could lead to sexual immaturity, hypogonadism, and delayed puberty.^[5]

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.^[32][33] Conservative estimates suggest that 25% of the world's population is at risk of zinc deficiency.^[34]

In the U.S., the Recommended Dietary Allowance (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.^[2] The following table summarizes most of the foods with significant quantities of zinc, listed in order of quantity per serving, unfortified.^[35] 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 foods. A meta-analysis 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, peas and soybeans grown in elevated CO₂ contained less zinc and iron.^[37] 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 3.3–9.3% 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.^[38]

Inadequate absorption

Acrodermatitis enteropathica is an inherited deficiency of the zinc carrier protein ZIP4 resulting in inadequate zinc absorption.^[6] It presents as growth retardation, severe diarrhea, hair loss, skin rash (most often around the genitalia and mouth) and opportunistic candidiasis and bacterial infections.^[6]

Numerous small bowel diseases which cause destruction or malfunction of the gut mucosa enterocytes and generalized malabsorption are associated with zinc deficiency.^{[citation needed]}

Increased loss

Exercising, high alcohol intake, and diarrhea all increase loss of zinc from the body.^[5][39] Changes in intestinal tract absorbability and permeability due, in part, to viral, protozoal, or bacteria pathogens may also encourage fecal losses of zinc.^[40]

Chronic disease

The mechanism of zinc deficiency in some diseases has not been well defined; it may be multifactorial.^{[citation needed]}

Wilson's disease, sickle cell disease, chronic kidney disease, chronic liver disease have all been associated with zinc deficiency.^[41][42] It can also occur after bariatric surgery, mercury exposure^[43][44] and tartrazine. ^{[citation needed]}

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.^[24]

Classification

Zinc deficiency can be classified as acute, as may occur during prolonged inappropriate zinc-free total parenteral nutrition; or chronic, as may occur in dietary deficiency or inadequate absorption.^[28]

Biofortification

Soil and foliar application of zinc fertilizer can effectively increase grain zinc and reduce the phytate:zinc ratio in grain.^[66][67] People who eat bread prepared from zinc enriched wheat have a significant increase in serum zinc.^{[citation needed]}

Zinc fertilization not only increases zinc content in zinc deficient crops, it also increases crop yields.^[65] 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 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.^[68] 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.