Zinc

Zinc is a trace element that is considered a micronutrient, meaning a nutrient needed in very small amounts. It is found in almost every living cell. The significance of zinc in human nutrition and public health was recognized relatively recently (1961), and it is now considered to have a wide range of essential biological roles in maintaining life and health.

Zinc is considered essential to maintain health. It is required for the activity of numerous metalloenzymes involved in metabolism, maintains the immune system that protects the body against disease, and also supports normal growth and development during pregnancy, childhood, and adolescence. It plays three crucial roles:

Additionally, zinc has the following functions:

Recent research reports indicate that zinc has been found to play a role in cell death (apoptosis) with implications for growth and development, as well as in a number of chronic diseases. Zinc is also actively taken up by synaptic vesicles that store the neurotransmitters released by nerve cells, suggesting a new role in neuronal activity and memory.

Zinc is found in the body in a form bound to proteins within cells, especially in the nucleus and cell membranes. The adult body contains about 1.5–2.5 g of zinc bound to various proteins. They occur in specialized areas of the brain that produce the chemical substances that can send messages from one nerve cell to another (neurotransmitters). Zinc is also found in the pancreas, adrenal gland, bones, liver, prostate, and in the reproductive organs. Most of the zinc (75–88%) in blood is found in a red blood cell metalloenzyme called carbonic anhydrase. In the plasma, zinc is bound to proteins, such as alpha-2-macroglobulin, albumin, transferrin and ceruloplasmin.

Zinc

SOURCE: Office of Dietary Supplements. National Institutes of Health. “Zinc: Fact Sheet for Health Professionals.” https://ods.od.nih.gov/factsheets/Zinc-HealthProfessional (accessed April 21, 2018).

Zinc is found in a wide variety of foods. Oysters are the richest zinc source per serving, but since they are not consumed regularly in the American diet, red meat and poultry provide the majority of dietary zinc. Other good zinc sources include beans, nuts, certain seafood, whole grains, fortified breakfast cereals, and dairy products. Zinc absorption is more efficient from a diet high in animal protein than a diet rich in plant proteins. Phytates, which are found in whole grain breads, cereals, legumes, and other products, are believed to decrease zinc absorption. Some good food sources of zinc include (per 1 oz. serving, or as indicated):

The Recommended Dietary Allowance (RDA) for zinc is:

Zinc in nutritional supplements is available as zinc gluconate, zinc oxide, zinc aspartate, zinc picolinate, zinc citrate, zinc monomethionine and zinc histidine. They are distributed as stand-alone or combination products, such as tablets, capsules, or liquids.

Fortified foods include many types of breakfast cereals that make it easier to consume the RDA for zinc. However, they also make it easier to consume too much zinc, especially if zinc supplements are also taken. Anyone considering zinc supplementation should first consider whether their needs could be met by dietary zinc sources and from fortified foods. Intakes between 150 and 450 mg of zinc per day lead to copper deficiency, impaired iron function, reduced immune function, and reduced levels of high-density lipoproteins, also known as “good cholesterol.” A few isolated cases of acute zinc toxicity have been reported for food or beverages contaminated with zinc present in galvanized containers. Single doses of 225–450 mg of zinc are known to induce vomiting. Milder gastrointestinal distress has been reported at doses of 50–150 mg/day of supplemental zinc.

The simultaneous administration of zinc supplements and certain antibiotics, such as tetracyclines and quinolones, may decrease absorption of the antibiotic with potential reduction of their action. To prevent this interaction, it is recommended to take the zinc supplements and antibiotics at least two hours apart. Metal chelating agents, like penicillamine, used to treat copper overload in Wilson disease, and diethyle-netriamine pentaacetate (DTPA), used to treat iron overload, can lead to severe zinc deficiency. Anticonvulsant drugs, such as sodium valproate, may also cause zinc deficiency. The prolonged use of diuretics may increase urinary zinc excretion, resulting in increased zinc losses. A medication used to treat tuberculosis, ethambutol, has been shown to increase zinc loss in rats.

Interactions of zinc taken with other supplements are as follows:

In the case of zinc deficiency, oral zinc therapy usually results in the complete disappearance of symptoms, but it must be maintained indefinitely in individuals with the acrodermatitis enteropathica.

Excessive intake can be corrected by bringing levels back to the RDA values.

It has been estimated that 82% of pregnant women worldwide are likely to have inadequate zinc intakes. Zinc deficiency has been associated with a number of pregnancy complications, including low birth weight, premature delivery, and labor and delivery complications.

The adverse effects of zinc deficiency on immune system function are also likely to increase complications in children who have infectious diarrhea. Persistent diarrhea contributes to zinc deficiency and malnutrition. Recent research has shown that zinc deficiency may also increase the harmful effects of toxins produced by diarrhea-causing bacteria like E. coli. Zinc supplementation in combination with drinking plenty of liquids has also been shown to significantly reduce the duration and severity of childhood diarrhea.

See also Veganism ; Vegetarianism .