Zinc deficiency
Zinc deficiency is defined either as insufficient body levels of zinc to meet the needs of the body, or as a zinc blood level below the normal range. However, since a decrease in blood concentration is only detectable after long-term or severe depletion, blood levels of zinc are not a reliable biomarker 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 is 8 mg/day for women and 11 mg/day for men.
The highest concentration of dietary zinc is found in oysters, meat, beans, 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 17% or 2 billion people worldwide.
Signs and symptoms
Skin, nails, and hair
Zinc deficiency may manifest as acne, eczema, xerosis, seborrheic dermatitis, or alopecia. It may also impair or possibly prevent wound healing.Mouth
Zinc deficiency can manifest as non-specific oral ulceration, stomatitis, or white tongue coating. Rarely it can cause angular cheilitis.Vision, smell, and taste
Severe zinc deficiency may disturb the sense of smell and taste. Night-blindness 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.Immune system
Impaired immune function in people with zinc deficiency can lead to the development of respiratory, gastrointestinal, or other infections, e.g., pneumonia. The levels of inflammatory cytokines 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, are impaired with zinc deficiency. Moderate and more severe zinc deficiencies are associated with behavioral abnormalities, such as irritability, lethargy, and depression. Zinc supplementation produces a rapid and dramatic improvement in hedonic tone 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 cause 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 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. The defective functioning of estrogen may mediate these effects via the estrogen receptor, which contains a zinc finger 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 of 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 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 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, hypogonadism, and delayed puberty.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 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 the top 10 entries are meat, beans, or nuts.
| Food | mg in one serving | Percentage of 11 mg recommended daily intake |
| Oysters, cooked, breaded, and fried, 3 ounces | 74.0 | 673% |
| Beef chuck roast, braised, 3 ounces | 7.0 | 64% |
| Crab, Alaska king, cooked, 3 ounces | 6.5 | 59% |
| Beef patty, broiled, 3 ounces | 5.3 | 48% |
| Cashews, dry roasted, 3 ounces | 4.8 | 44% |
| Lobster, cooked, 3 ounces | 3.4 | 31% |
| Pork chop, loin, cooked, 3 ounces | 2.9 | 26% |
| Baked beans, canned, plain, or vegetarian, | 2.9 | 26% |
| Almonds, dry roasted, 3 ounces | 2.7 | 25% |
| Chicken, dark meat, cooked, 3 ounces | 2.4 | 22% |
| Yogurt, fruit, low fat, 8 ounces | 1.7 | 15% |
| Shredded wheat, unfortified, | 1.5 | 14% |
| Chickpeas, cooked, | 1.3 | 12% |
| Cheese, Swiss, 1 ounce | 1.2 | 11% |
| Oatmeal, instant, plain, prepared with water, 1 packet | 1.1 | 10% |
| Milk, low-fat or non-fat, | 1.0 | 9% |
| Kidney beans, cooked, | 0.9 | 8% |
| Chicken breast, roasted, skin removed, breast | 0.9 | 8% |
| Cheese, cheddar, or mozzarella, 1 ounce | 0.9 | 8% |
| Peas, green, frozen, cooked, | 0.5 | 5% |
| Flounder or sole, cooked, 3 ounces | 0.3 | 3% |
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. 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.
Inadequate absorption
is an inherited deficiency of the zinc transporter ZIP4 protein, resulting in inadequate zinc absorption. It presents as retarded growth, severe diarrhea, hair loss, skin rash 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 increase the body's loss of zinc. 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, sickle cell disease, chronic kidney disease, and chronic liver disease have all been associated with zinc deficiency. It can also occur after bariatric surgery and exposure to mercury.
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 cannot store zinc, regular intake is necessary. Excessively low zinc intake can lead to zinc deficiency, negatively impacting 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 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, RNA transcription, cell division, and cell activations. However, having too much or too little zinc can compromise these functions.Some 50 enzymes are dependent on zinc for their roles in catalysis. 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 activity of nucleoproteins and 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 is a Candida albicans protein that scavenges host zinc.