Zinc is a component of more than 100 enzymes associated with various metabolic processes, including the synthesis of the nucleic acids RNA and DNA. It is required for the transport of Vitamin A from the liver, and as part of superoxide dismutase (SOD) helps protect cells from free radicals. Zinc is also required for normal growth and development, reproductive development and function, and to support the immune system, where it has been shown to increase T-lymphocytes and enhance other white blood cell functions.

The body contains about 1.5 to 2.5 g of zinc, of which the kidneys, liver, pancreas, eyes, prostate and bone contain larger concentrations, however they do not function as zinc reserves, so the body depends on enough dietary intake to meet its daily requirements. Zinc is lost in sweat and through food processing. In addition, with zinc being water-soluble, canning or cooking in water can deplete the amounts of zinc in food, and less zinc is also absorbed when it is bound with phytates or oxalates found in grains and vegetables, and when high amounts of other trace minerals such as copper, iron, calcium, and some toxic metals (cadmium, lead) are present at the same time.

Zinc deficiency has been implicated as a factor with birth defects and low birth weight, impaired learning, as well as delayed sexual development. Additional zinc intake may help with the loss of smell or taste sensation, wound healing, anorexia / loss of appetite, paranoia, depression, strong body odor, impotence, certain hair, nail and joint / arthritic problems, benign prostatic hypertrophy, impotence, cataracts and optic neuritis, as well as skin conditions such as acne and dermatitis.

Zinc is necessary to maintain normal serum Testosterone levels, whereby inadequate zinc levels prevent the pituitary gland from releasing luteinizing and follicle stimulating hormones, which stimulate testosterone production. Zinc also inhibits the aromatase enzyme that converts testosterone into excess estrogen. The testosterone to estrogen ratio in men declines with aging from a high of about 50:1 to half of that, or even a low of 10:1, resulting in higher estradiol (estrogen) activity, which subsequently increases the risk of heart disease, Weight Gain, or even obesity. One reason is that fat cells contain aromatase, so more fat cells translate into more testosterone being converted to estrogen. This is further aggravated by alcohol consumption, which lowers zinc and increases estrogen, and so magnifies the problem.

What is Zinc?
Zinc is a metal. It is called an "essential trace element" because very small amounts of zinc are necessary for human health. Zinc is used for treatment and prevention of zinc deficiency and its consequences, including stunted growth and acute diarrhea in children, and slow wound healing.

It is also used for boosting the immune system, treating the common cold and recurrent ear infections, and preventing lower respiratory infections. It is also used for malaria and other diseases caused by parasites.

Some people use zinc for an eye disease called macular degeneration, for night blindness, and for cataracts. It is also used for asthma; diabetes; high blood pressure; acquired immunodeficiency syndrome (AIDS); and skin conditions such as psoriasis, eczema, and acne. Other uses include treating attention deficit-hyperactivity disorder (ADHD), blunted sense of taste (hypogeusia), ringing in the ears (tinnitus), severe head injuries, Crohn's disease, Alzheimer's disease, Down syndrome, Hansen's disease, ulcerative colitis, peptic ulcers and promoting weight gain in people with eating disorders such as anorexia nervosa.
Some people use zinc for benign prostatic hyperplasia (BPH), male infertility, erectile dysfunction (ED), weak bones (osteoporosis), rheumatoid arthritis, and muscle cramps associated with liver disease. It is also used for sickle cell disease and inherited disorders such as acrodermatitis enteropathica, thalassemia, and Wilson's disease. Some athletes use zinc for improving athletic performance and strength.

Where it is found
Shellfish, beef, and other red meats are rich sources of zinc. Nuts and legumes are relatively good plant sources of zinc. Zinc bioavailability (the fraction of zinc retained and used by the body) is relatively high in meat, eggs, and seafood because of the relative absence of compounds that inhibit zinc absorption and the presence of certain amino acids (cysteine and methionine) that improve zinc absorption. The zinc in whole grain products and plant proteins is less bioavailable due to their relatively high content of phytic acid, a compound that inhibits zinc absorption. The enzymatic action of yeast reduces the level of phytic acid in foods. Therefore, leavened whole grain breads have more bioavailable zinc than unleavened whole grain breads.

The zinc content of some relatively zinc-rich foods is listed in milligrams (mg) in the table below:

The Institute of Medicine has established Adequate Intake (AI) levels of zinc for infants birth to 6 months is 2 mg/day. For older infants, children, and adults, Recommended Dietary Allowance (RDA) quantities of zinc have been established: infants and children 7 months to 3 years, 3 mg/day; 4 to 8 years, 5 mg/day; 9 to 13 years, 8 mg/day; girls 14 to 18 years, 9 mg/day; boys and men age 14 and older, 11 mg/day; women 19 and older, 8 mg/day; pregnant women 14 to 18, 13 mg/day; pregnant women 19 and older, 11 mg/day; lactating women 14 to 18, 14 mg/day; lactating women 19 and older, 12 mg/day.

The typical North American male consumes about 13 mg/day of dietary zinc; women consume approximately 9 mg/day.

The Tolerable Upper Intake Levels (UL) of zinc for people who are not receiving zinc under medical supervision: Infants birth to 6 months, 4 mg/day; 7 to 12 months, 5 mg/day; children 1 to 3 years, 7 mg/day; 4 to 8 years, 12 mg/day; 9 to 13 years, 23 mg/day; 14 to 18 years (including pregnancy and lactation), 34 mg/day; adults 19 years and older (including pregnancy and lactation), 40 mg/day.

APPLIED TO THE SKIN:

Possible Side effects / Precautions / Possible Interactions:
Zinc is likely safe for most adults when applied to the skin, or when taken by mouth in amounts not larger than 40 mg per day. In some people, zinc might cause nausea, vomiting, diarrhea, metallic taste, kidney and stomach damage, and other side effects. Using zinc on broken skin may cause burning, stinging, itching, and tingling.

Taking high amounts of zinc is likely unsafe. High doses above the recommended amounts might cause fever, coughing, stomach pain, fatigue, and many other problems.

Zinc nose sprays (Zicam, Cold-Eeze) are possibly unsafe. These products may cause loss of ability to smell. In June 2009, the US Food and Drug Administration (FDA) advised consumers not to use certain zinc-containing nose sprays (Zicam) after receiving over 100 reports of loss of smell. The maker of these zinc-containing nose sprays has also received several hundred reports of loss of smell from people who had used the products. Avoid using zinc nose sprays.

Special precautions & warnings:
Pregnancy and breast-feeding: Zinc is likely safe for most pregnant and breast-feeding women when used in the recommended daily amounts (RDA). Pregnant women over 18 should not take more than 40 mg of zinc per day; pregnant women age 14 to 18 should not take more than 34 mg per day. Breast-feeding women over 18 should not take more than 40 mg of zinc per day; breast-feeding women age 14 to 18 should not take more than 34 mg per day.
HIV (human immunodeficiency virus)/AIDS: Do not take zinc if you have HIV/AIDS. Zinc might shorten your life.

Possible Interactions
Do not take this combination.
Penicillamine
Penicillamine is used for Wilson's disease and rheumatoid arthritis. Zinc might decrease how much penicillamine your body absorbs and decrease the effectiveness of penicillamine. Take zinc and penicillamine at least 2 hours apart.

Be cautious with this combination.
Antibiotics (Quinolone antibiotics)
Zinc might decrease how much antibiotic the body absorbs. Taking zinc along with some antibiotics might decrease the effectiveness of some antibiotics. To avoid this interaction, take antibiotics at least 2 hours before or 4-6 hours after zinc supplements.

Some of these antibiotics that might interact with zinc include ciprofloxacin (Cipro), levofloxacin (Levaquin), ofloxacin (Floxin), moxifloxacin (Avelox), gatifloxacin (Tequin) enoxacin (Penetrex), norfloxacin (Chibroxin, Noroxin), sparfloxacin (Zagam), trovafloxacin (Trovan), and grepafloxacin (Raxar).

Antibiotics (Tetracycline antibiotics)
Zinc can attach to tetracyclines in the stomach. This decreases the amount of tetracyclines that can be absorbed. Taking zinc with tetracyclines might decrease the effectiveness of tetracyclines. To avoid this interaction, take tetracyclines 2 hours before or 4-6 hours after taking zinc supplements.
Some tetracyclines include demeclocycline (Declomycin), minocycline (Minocin), and tetracycline (Achromycin, Sumycin).

Cisplatin (Platinol-AQ)
Cisplatin (Platinol-AQ) is used to treat cancer. Taking zinc along with EDTA and cisplatin (Platinol-AQ) might inactivate cisplatin (Platinol-AQ) therapy. It is not known for sure, though, if the amount of interference caused by zinc is significant.

Be watchful with this combination.
Amiloride (Midamor)
Amiloride (Midamor) is used as a "water pill" to help remove excess water from the body. Another effect of amiloride (Midamor) is that it can increase the amount of zinc in the body. Taking zinc supplements with amiloride (Midamor) might cause you to have too much zinc in your body.

Research studies / References