All you need to know about Zinc
Zinc is a metallic chemical element with the symbol Zn and atomic number 30. In non-scientific context it is sometimes called spelter.
Its role in health is as contributory in metabolic, action of enzymes, is essential for growth and reproduction, and also supports immune function.
Zn is an essential trace element, indispensable for sustaining all life and it is the key factor in prostate gland function and reproductive organ growth.
It is estimated that 3,000 of the hundreds of thousands of proteins in the human body contain Zn prosthetic groups, one type of which is the so-called Zn finger, and most of Zn is contained in muscles and bones.
In addition, there are over a dozen types of cells in the human body that secrete Zn ions, and the roles of these secreted Zn signals in medicine and health are now being actively studied. Zn ions are at present considered to be neurotransmitters.
Cells in the salivary gland, prostate, immune system and intestine use Zn signaling.
In humans, Zinc is a cofactor for over 100 enzymes, notably certain metalloenzymes. It is absorbed 15 to 40 percent in the intestines, with higher absorption when Zn status is low.
Once absorbed, it may be held metallothionein reserves within the intestines or the liver. Zn is also recycled through the pancreas, which secretes Zn-containing enzymes into the intestines at mealtimes in a process called enteropancreatic circulation.
Zn is transported through the blood by albumin and transferrin. Since transferrin also transports iron, excessive iron reduces Zn absorption, and vice-versa. A similar situation exists with Zn and copper.
As of 2005 an effective measure of Zn status in humans "remained elusive", although a method involving reverse transcription polymerase chain reaction showed promise. Plasma Zinc concentrations are insensitive indicators of Zn status since a narrow homeostatic range is maintained in the body.
Zinc is also participating in olfaction: the olfactory receptors contain Zn binding sites and a deficiency in Zn causes anosmia.
Zn is an activator of certain enzymes important in the transport of carbon dioxide in vertebrate blood. It is also required in plants for leaf formation, the synthesis of indole acetic acid (auxin) and anaerobic respiration (alcoholic fermentation).
Zn is a good lewis acid, making it a useful catalytic agent in hydroxylation and other enzymatic reactions. Furthermore, Zn has flexible coordination geometry, allowing enzymes using Zn to rapidly shift conformations and perform biological reactions.
Signs of Zn deficiency include hair loss, skin lesions, diarrhea, and wasting of body tissues. Eyesight, taste, smell and memory are also connected with Zn. A deficiency in Zn can cause malfunctions of these organs and functions. Congenital abnormalities causing Zn deficiency may lead to a disease called Acrodermatitis enteropathica. Conservative opinions suggest that 25% of the world's population is at risk of Zn deficiency.
Zn deficiency during pregnancy can negatively affect both the mother and fetus. Animal studies indicate that maternal Zn 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 Zn deficient animals. These effects may be mediated by the defective functioning of estrogen via the estrogen receptor, which contains a Zn 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 Zn deficiency. However, a review on Zn supplementation trials during pregnancy did not report a significant effect of Zn supplementation on neonatal survival.
Cognitive and motor function may also be impaired in Zinc deficient children. Zn deficiency can interfere with many organ systems especially when it occurs during a time of rapid growth and development when nutritional needs are high, such as during infancy. In animal studies, rats who were deprived of Zn during early fetal development exhibited increased emotionality, poor memory, and abnormal response to stress which interfered with performance in learning situations.
It is rarely recognized that lack of Zn can contribute to acne. Leukonychia, white spots on the fingernails, are often seen as an indication of Zn deficiency.
High dose of Zn, 30 mg 1-3 times a day, prevents dysmenorrhea.
Plasma Zn levels have been found to be dependent upon vitamins A and D. This suggests that a Vitamin A or D deficiency could cause a secondary Zn deficiency. And that for, treatment of Zn deficiency one should ensure adequate vitamin A and D intake.
The studies determined that a ten-day therapy of Zn treatment can considerably reduce the duration and severity of diarrheal episodes, decrease stool output, and lessen the need for hospitalization. Zn may also prevent future diarrhea episodes for up to three months.
The current World Health Organization recommendation for diarrhea control includes the use of 20 mg per day of Zn supplementation for 10 to 14 days (10 mg per day for infants under the age of six months).
Zn supplementation has been shown to reduce diarrhea prevalence and mortality in children younger than 5 years of age.
Zinc and Hunger
The influence of Zn on hunger is complex and likely depends upon the status of other nutrients, the developmental stage of the animal, and percentage body fat. Some research groups have argued for a role of Zn deficiency decreasing appetite, while others have shown Zn ingestion can reduce feelings of hunger by increasing Leptin levels.
Zn deficiency may cause a decrease in appetite -- which could degenerate in anorexia nervosa. Appetite disorders, in turn, cause malnutrition and, notably, inadequate Zn intake. Anorexia itself is a cause of Zn deficiency, thus leading to a vicious cycle: the worsening of anorexia worsens the Zn deficiency.
The use of Zinc in the treatment of anorexia nervosa has been advocated since 1979 by Bakan. At least 15 trials showed that Zn improved weight gain in anorexia. A 1994 randomized, double-blind, placebo-controlled trial showed that Zn (14 mg per day) doubled the rate of body mass increase in the treatment of anorexia nervosa.
A wide variety of foods contain Zinc.
Oysters contain more Zn per serving than any other food, and far lesser degree in most animal proteins, beans, nuts, almonds, pumpkin seeds, sunflower seeds, red meat and poultry which provide the majority of Zn in the American diet.
Other good food sources include beans, nuts, certain types of seafood (such as crab and lobster), whole grains, fortified breakfast cereals, and dairy products.
Thus, the bioavailability of Zn from grains and plant foods is lower than that from animal foods, although many grain—and plant-based foods are still good sources of Zn.
Phytates, which are found in whole grain breads, cereals, legumes and other products, have been known to decrease Zn absorption.
Clinical studies have found that Zn, combined with antioxidants, may delay progression of age-related macular degeneration. Soil conservation analyzes the vegetative uptake of naturally occurring Zn in many soil types.
The US recommended dietary allowance of Zinc from puberty on is 11mg for males and 8mg for females, with higher amounts recommended during pregnancy and lactation.
Other sources include fortified food and dietary supplements, which come in various forms.
A 1998 review concluded that Zn oxide, one of the most common supplements in the United States, and Zn carbonate are nearly insoluble and poorly absorbed, and cited studies which found low plasma Zn concentrations after Zn oxide and Zn carbonate consumption relative to the plasma concentrations seen after consumption of Zn acetate and sulfate salts.
For fortification, however, a 2003 review recommended Zn oxide in cereals as cheap, stable, and as easily absorbed as more expensive forms.
A 2005 study found that various compounds of Zn, including oxide and sulfate, did not show statistically significant differences in absorption when added as fortifiers to maize tortillas.
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