Zinc is an important element that is found in every cell in the body. More than 300 enzymes in the body need zinc in order to function properly. Although the amount of zinc we need in our daily diet is tiny, it's very important that we get it. However, the evidence suggests that many of us do not get enough. Mild zinc deficiency seems to be fairly common, and for this reason taking a zinc supplement at nutritional doses may be a good idea.

However, taking too much zinc isn’t a good idea—it can cause toxicity. In this article, we discuss the possible uses of zinc at various doses.

Requirements/Sources
Requirements

The official US recommendations for daily intake of zinc are as follows:

  • Infants
    • 0-6 months: 2 mg
    • 7-12 months: 3 mg
  • Children
    • 1-3 years: 3 mg
    • 4-8 years: 5 mg
  • Males
    • 9-13 years: 8 mg
    • 14 years and older: 11 mg
  • Females
    • 9-13 years: 8 mg
    • 14-18 years: 9 mg
    • 19 years and older: 8 mg
  • Pregnant Women
    • 18 years and younger: 13 mg
    • 19 years and older: 11 mg
  • Nursing Women
    • 18 years and younger: 14 mg
    • 19 years and older: 12 mg
Sources

Oysters have a very high zinc content—a 3-ounce serving of cooked oysters has about 74 milligrams of zinc. Besides oysters, other types of shellfish, along with meat and chicken are high in zinc. In the table below, the National Institutes of Health's Office of Dietary Supplements offers an extensive list of foods that are high in zinc:207

FoodServing size Zinc content
(milligrams [mg]) 		% Daily Value
Oysters, cooked3 ounces74493
Beef chuck roast, braised3 ounces747
Alaska king crab, cooked3 ounces6.543
Beef patty, broiled3 ounces5.335
25% fortified breakfast cereal¾ cup3.825
Lobster, cooked3 ounces3.423
Pork chop, cooked3 ounces2.919
Baked beans, canned½ cup2.919
Chicken (dark meat), cooked3 ounces2.416
Fruit yogurt, low-fat8 ounces1.711
Cashews, dry roasted1 ounce1.611
Chickpeas, cooked½ cup1.39
Swiss cheese1 ounce1.28
Instant oatmeal1 serving1.17
Milk, low-fat or non-fat1 cup1.07
Almonds, dry roasted`1 ounce0.96
Kidney beans, cooked½ cup0.96
Chicken breast, roasted½ breast0.96
Cheddar or mozzarella cheese1 ounce0.96
Green peas, cooked½ cup0.53

Zinc can also be taken as a nutritional supplement, in one of many forms. Zinc citrate, zinc acetate, or zinc picolinate may be the best absorbed, although zinc sulfate is less expensive. When you purchase a supplement, you should be aware of the difference between the milligrams of actual zinc that the product contains (so-called elemental zinc) and the total milligrams of the zinc product, which includes the weight of the sulfate, picolinate, and so forth. All dosages given in this article refer to elemental zinc (unless otherwise stated).

Zinc Deficiency

The average diet in the developed world may provide insufficient zinc, especially in women, adolescents, infants, and the elderly.1-5,163 Thus, it may be a wise idea to increase your intake of zinc on general principles.

Zinc Absorption

Various drugs may tend to reduce levels zinc in the body by inhibiting its absorption or increasing its excretion. These include captopril and possibly other ACE inhibitors, oral contraceptives, thiazide diuretics,6-12,31,32 and drugs which reduce stomach acid (including H2blockers and proton pump inhibitors). Certain nutrients may also inhibit zinc absorption, including calcium, soy, manganese, copper, and iron.13-29 Contrary to previous reports, folate is not likely to have this effect.30

Therapeutic Dosages

For most purposes, zinc should simply be taken at the recommended daily requirements listed previously.

Some evidence suggests that 30 mg of zinc daily may be helpful for acne. This is a safe dose for most people. However, in most studies of zinc for acne, a much higher dose was used: 90 mg daily or more. Doses this high should only be used under physician supervision (see Safety Issues). Potentially dangerous doses of zinc have also been recommended for sickle-cell anemia, macular degeneration, and rheumatoid arthritis.

For best absorption, zinc supplements should not be taken at the same time as high-fiber foods.33,34 However, many high-fiber foods provide zinc in themselves.

Zinc gluconate may be slightly better absorbed than zinc oxide.180

When taking zinc long-term it is advisable to take 1 mg to 3 mg of copper daily as well, because zinc supplements can cause copper deficiency.35,36 Zinc may also interfere with magnesium37 and iron38 absorption.

Zinc is used topically in lozenge or nasal gel form for the treatment of colds. When using zinc this way, the purpose is not to increase zinc levels in your body, but to interfere with the action of viruses in the back of your throat or in the nose. It appears that of the common forms of zinc, only zinc gluconate and zinc acetate have the required antiviral properties.39,40 Certain sweeteners and flavorings used in lozenges can block zinc's antiviral action. Dextrose, sucrose, mannitol, and sorbitol appear to be fine, but citric acid and tartaric acid are not. The information on glycine as a flavoring agent is a bit equivocal.

Note: When using zinc nasal gel products, do not deeply inhale, as this may cause severe pain. Rather, simply squeeze the gel into the nose, according to the directions.

Therapeutic Uses

Use of zinc nasal spray or zinc lozenges at the beginning of a cold may reduce the duration and severity of symptoms, but study results are somewhat inconsistent.41,42,164,181-183 These treatments are thought to work by directly interfering with viruses in the nose and throat, and involve relatively high doses of zinc used for a short time.

Zinc can also be taken long-term at nutritional doses orally to improve overall immunity and reduce risk of infection;43,44, 197 however, this approach probably only works if you are deficient in zinc to begin with.

A significant body of evidence suggests that oral zinc can reduce symptoms of acne.48-53,165 But, in most studies, potentially toxic doses were used, and in any case, the benefits appear to be rather slight.

Growing evidence suggests that oral zinc, especially in combination with antioxidants, can help slow the progression of macular degeneration.105,106,156 Oral zinc has also shown promise for sickle cell anemia,54,161,166,204 ADHD,172,173 and stomach ulcers.55,56 Zinc has also been shown to be beneficial for acute diarrhea in children, the most convincing evidence coming from studies done in developing countries.202,203 This suggests that zinc is most useful for this condition in the presence of a nutritional deficiency.

Topical zinc may be helpful for cold sores.45

Zinc has shown some promise for treating dysgeusia (impaired taste sensation). In a study of 50 people with idiopathic dysgeusia (impaired taste sensation of no known cause), use of zinc at a rather high dose of 140 mg daily improved taste ability.184 Another study enrolled seniors with dysgeusia and gave them either placebo or 30 mg of zinc daily; the results were equivocal.199 Dysgeusia can also be caused by radiation therapy in the vicinity of the mouth, but the overall evidence regarding the use of zinc for this purpose is more negative than positive.167,198 Kidney dialysis also impairs taste sensation, but once more zinc supplements failed to prove effective.174 ( Note: Use of any mineral supplement by people undergoing kidney dialysis is potentially dangerous.)

In one study, use of zinc appeared to modestly decrease inflammation of the mucous membranes and skin caused by radiation therapy.195

Weak and/or contradictory results have been seen in studies of zinc for anorexia nervosa,81-83,162 depression,175 rheumatoid arthritis,57-62,159,160 enhancing sexual function in men on kidney dialysis,100,168,169 tinnitus,110,170 and warts.185

Some, but not all, studies have found that HIV-positive people tend to be deficient in zinc, with levels dropping lower in more severe disease.64-69 Higher zinc levels have been linked to better immune function and higher CD4+ cell counts, whereas zinc deficiency has been linked to increased risk of dying from HIV.70-72 One preliminary study among people taking AZT found that 30 days of zinc supplementation led to decreased rates of opportunistic infection over the following 2 years.73 However, other research has linked higher zinc intake to more rapid development of AIDS.74,75 Another failed to find that zinc supplementation reduces diarrhea associated with HIV.193 The bottom line: If you have HIV, consult your physician before supplementing with zinc.

Although the evidence that zinc works is not yet meaningful, the supplement is sometimes recommended for the following conditions as well: Alzheimer's disease,77-80 and minor memory loss in seniors,196 benign prostatic hyperplasia,87-93 bladder infection, cataracts, diabetes,94-96 Down's syndrome,97-99 infertility in men,76,188 inflammatory bowel disease ( ulcerative colitis and Crohn's disease),101-104 osteoporosis,107 periodontal disease, prostatitis,108 psoriasis, and wound and burn healing.111-113

An 8-week, double-blind trial of zinc at 67 mg daily failed to find any benefit for eczema symptoms.158

What Is the Scientific Evidence for Zinc?
Colds

Use of lozenges containing zinc gluconate or zinc acetate have shown somewhat inconsistent, but generally positive results for reducing the severity and duration of the common cold. For example, in a double-blind trial, 100 people who were experiencing the early symptoms of a cold were given a lozenge that either contained 13.3 mg of zinc from zinc gluconate or a placebo.116 Participants took the lozenges several times daily until their cold symptoms subsided. The results were impressive. Coughing disappeared within 2.2 days in the treated group versus 4 days in the placebo group. Sore throat disappeared after 1 day versus 3 days in the placebo group, nasal drainage in 4 days (versus 7 days), and headache in 2 days (versus 3 days). Positive results have also been seen in double-blind studies of zinc acetate.117,118,201 While not all studies have been supportive,119 on balance, results appear to favor the effectiveness of zinc lozenges for treating symptoms of the common cold.120,186, 206

It has been suggested that the exact formulation of the zinc lozenge plays a significant role in its effectiveness.40 According to this view, certain flavoring agents, such as citric acid and tartaric acid, might prevent zinc from inhibiting viruses. In addition, chemical forms of zinc other than zinc gluconate or zinc acetate might be ineffective. Zinc sulfate in particular might not work.121 Along the same lines, sweeteners such as sorbitol, sucrose, dextrose, and mannitol are said to be fine, while glycine has been discussed in an equivocal manner.

Use of zinc in the nose is somewhat more controversial.187 In addition to showing inconsistent results in studies, use of zinc nasal gel can cause pain and possibly loss of sense of smell. ( See Safety Issues.)

For example, in a double-blind, placebo-controlled trial of a widely available zinc nasal gel product , 213 people with a newly starting cold used one squirt of zinc gluconate gel or placebo gel in each nostril every 4 hours while awake.114 The results were significant: treated participants stayed sick an average of 2.3 days, while those receiving placebo were sick for an average of 9 days, a 75% reduction in the duration of symptoms. Somewhat more modest, but still significant relative benefits were seen with zinc nasal gel in a double-blind, placebo-controlled study of 80 people with colds.164 However, another study, this one involving 77 people, failed to find benefit even with near constant saturation of the nasal passages with zinc gluconate nasal spray.189 Furthermore, a study of 91 people using the standard commercially available nasal spray failed to find benefit.190 Yet another double-blind, placebo-controlled trial, this one enrolling 185 individuals, failed to find benefit with zinc nasal spray.115 However, this study used a much lower amount of zinc—50 times lower—per squirt of spray than was used in the studies just described.

Other than its direct affect on viruses during an infection, zinc supplements (not lozenges) may play a role in reducing the risk of coming down with a cold in the first place. In a review of 2 randomized trials, which included 394 healthy children, researches found that the groups who took zinc had fewer colds, school absences, and prescriptions for antibiotics.206

In a review of 17 randomized trials with 2,121 patients, oral zinc started within 3 days of cold symptom appearance showed mixed results when compared to placebo or no treatment. Four trials with 412 patients showed no significant decrease in symptom severity. However, the risk of being symptomatic after 7 days was reduced significantly in 9 trials with 1,325 patients. Cold symptoms were reduced by an average of 2.6 days in an analysis of 5 trials with 371 adults. No significant differences in cold symptom duration were found in 3 trials with 563 children.208

Chronic zinc deficiency is known to weaken the immune system.123 Although low levels of zinc are uncommon in healthy children and adults living in developed countries, deficiencies may be found among the elderly and are widespread among populations in developing countries. A 1-year, double-blind study of 50 nursing home residents found that zinc supplements reduced rates of infection compared to placebo.197 Additionally, in a 2-year study of nursing home residents, participants given zinc and selenium developed illnesses less frequently than those given placebo.122

Numerous studies in developing countries have also found benefit. For example, a 6-month, double-blind, placebo-controlled study of 609 preschool children in India found that zinc supplements reduced the rate of respiratory infections by 45%.124 In addition, more than 10 other studies performed in developing countries have also found that zinc supplements were helpful for preventing respiratory and other infections in children, and that zinc might reduce symptom severity.125,194,200

Cold Sores

Cold sores are infections caused by the herpes virus. One study suggests that topical zinc may be helpful. In this trial, 46 individuals with cold sores were treated with a zinc oxide cream or placebo every 2 hours until cold sores resolved.126 The results showed that individuals using the cream experienced a reduction in severity of symptoms and a shorter time to full recovery.

Zinc is thought to interfere with the ability of the herpes virus to reproduce itself. As with colds, the formulation of zinc must be properly designed to release active zinc ions. This study used a special zinc oxide and glycine formulation.

Some participants in this study experienced burning and inflammation caused by the zinc itself, but this seldom caused a serious problem.

Macular Degeneration

Macular degeneration is one of the most common causes of vision loss in the elderly. 

A double-blind, placebo-controlled trial evaluated the effects of zinc with or without antioxidants on the progression of macular degeneration in 3,640 individuals in the early stage of the disease.156 Participants were randomly assigned to receive one of the following: antioxidants ( vitamin C 500 mg, vitamin E 400 IU, and beta-carotene 15 mg), or zinc (80 mg) and copper (2 mg), antioxidants plus zinc, or placebo. (Copper was administered along with zinc to prevent zinc-induced copper deficiency.)

The results suggest that zinc (alone or, even better, with antioxidants) significantly slowed the progression of the disease.

Previous studies of zinc for macular degeneration found mixed results, but they were much smaller.141,142

There is also some evidence that making sure to get your dietary requirement of zinc on a daily basis over many years might reduce the risk of developing macular degeneration later in life.143

Keep in mind that the dosages of zinc used in most of these studies are rather high, and should be used only under a physician's supervision.

Attention Deficit Hyperactivity Disorder

Zinc has shown some promise for treatment of attention deficit hyperactivity disorder (ADHD). In a large (approximately 400-participant), double-blind, placebo-controlled study, use of zinc at a dose of 40 mg daily produced statistically significant benefits as compared to placebo among children not using any other treatment.176 This dose of zinc, while higher than nutritional needs, should be safe. However, the benefits seen were quite modest: about 28% of the participants given zinc showed improvement as compared to 20% in the placebo group.

Another, much smaller double-blind, placebo-controlled study evaluated whether zinc at 15 mg per day could enhance the effect of Ritalin.177 Again, modest benefits were seen.

Finally, extremely weak evidence hints that zinc might enhance the effectiveness of evening primrose oil for ADHD.178

Acne

Studies suggest that people with acne have lower-than-normal levels of zinc in their bodies.127-129 This fact alone does not prove that taking zinc supplements will help acne, but several small double-blind studies involving a total of more than 300 people have found generally positive results.

In one of these studies, 54 people were given either placebo or 135 mg of zinc (as zinc sulfate) daily. Zinc produced slight, but measurable benefits.130 Similar results have been seen in other studies using 90 mg to 135 mg of zinc daily.131-134 Some evidence suggests that a lower and safer dose, 30 mg daily, may offer some benefits.135,165 In some studies, however, no benefits were seen.136,137

Two studies have compared zinc against a standard treatment for acne, the antibiotic tetracycline. One study found that zinc was as effective as tetracycline taken at 250 mg daily,138 but another found the antibiotic far more effective when taken at 500 mg daily.139

Keep in mind that the dosages of zinc used in most of these studies are rather high; case reports indicate that people have made themselves extremely ill by taking zinc in hopes of treating their acne symptoms.147,171 Doses of zinc higher than the recommended safe levels (see Safety Issues) should be used only under a physician's supervision.

Sickle-cell Disease

Children with sickle cell disease often do not grow normally. There is some evidence that people with sickle cell disease are more likely than others to be deficient in zinc.161 Since zinc deficiency can also cause delayed growth, zinc supplementation at nutritional doses has been suggested for children with sickle cell disease. In a placebo-controlled study, 42 children (ages 4 to 10) with sickle cell disease were given either zinc supplements (10 mg of zinc daily) or placebo for a period of 1 year.161 Results showed that by the end of the study, the participants given zinc showed enhanced growth compared to those given placebo. Curiously, researchers did not find any solid connection between the severity of zinc deficiency and the extent of response to treatment.

Zinc is thought to have a stabilizing effect on the cell membrane of red blood cells in people with sickle cell disease. For this reason, it has been tried as an aid for preventing sickle cell crisis. In a double-blind, placebo-controlled study of 145 people with sickle cell disease conducted in India, participants received either placebo or about 50 mg of zinc 3 times daily.54 During 18 months of treatment, the zinc-treated subjects had an average of 2.5 crises, compared to 5.3 for the placebo group. However, zinc didn't seem to reduce the severity of a crisis, as measured by the number of days spent in the hospital for each crisis.

Sickle cell disease can also cause skin ulcers (nonhealing sores). In a 12-week, placebo-controlled trial, use of zinc at 88 mg 3 times per day for 12 weeks enhanced the rate of ulcer healing.166

Warning: The high dosages of zinc used in the last two studies can cause dangerous toxicity and should be taken (if at all) only under the supervision of a doctor. The nutritional dose described in the first study, however, is safe. (See Safety Issues.)

Safety Issues

Zinc taken orally seldom causes any immediate side effects other than occasional stomach upset, usually when it's taken on an empty stomach. Some forms do have an unpleasant metallic taste. Use of zinc nasal gel, however, has been associated with anosmia (loss of sense of smell).191 In fact, After receiving over 130 reports of anosmia, the FDA warned consumers and healthcare providers in 2009 to discontinue use of certain Zicam Cold Remedy intranasal zinc-containing products, including Zicam Cold Remedy Nasal Gel, Cold Remedy Nasal Swabs and Cold Remedy Swabs in kids size.205 Furthermore, if the gel is inhaled too deeply, severe pain may occur.

Long-term use of oral zinc at dosages of 100 mg or more daily can cause a number of toxic effects, including severe copper deficiency, impaired immunity, heart problems, and anemia.144-147 Zinc at a dose of more than 50 mg daily might reduce levels of HDL ("good") cholesterol.192 In addition, very weak evidence hints that use of zinc supplements might increase risk of prostate cancer in men.179

A bad taste in the mouth and nausea were the most common side effects in an analysis of 17 trials with 2,121 patients taking zinc to reduce the duration and severity of cold symptoms.208

The US government has issued recommendations regarding "tolerable upper intake levels" (ULs) for zinc. The UL can be thought of as the highest daily intake over a prolonged time known to pose no risks to most members of a healthy population. The ULs for zinc are as follows:157

  • Infants
    • 0-6 months: 4 mg
    • 7-12 months: 5 mg
  • Children
    • 1-3 years: 7 mg
    • 4-8 years: 12 mg
    • 9-13 years: 23 mg
  • Males and Females
    • 14-18 years: 34 mg
    • 19 years and older: 40 mg
  • Pregnant Women and Nursing Women
    • 18 years or younger: 34 mg
    • 19 years and older: 40 mg

There are also some interactions between zinc and certain medications to consider:

Use of zinc can interfere with the absorption of the drug penicillamine and also antibiotics in the tetracycline or fluoroquinolone (Cipro, Floxin) families.148-153

The potassium-sparing diuretic amiloride was found to significantly reduce zinc excretion from the body.154 This means that if you take zinc supplements at the same time as amiloride, zinc accumulation could occur. This could lead to toxic side effects. However, the potassium-sparing diuretic triamterene does not seem to cause this problem.155

Interactions You Should Know About

If you are taking:

  • ACE inhibitors; estrogen-replacement therapy; oral contraceptives; thiazide diuretics; or medications that reduce stomach acid (such as H 2 blockers [ Zantac ] or proton pump inhibitors [ Prilosec ]): You may need to take extra zinc.
  • Amiloride: This medication could reduce zinc excretion from the body, leading to zinc accumulation, which could cause toxic side effects. Do not take zinc supplements unless advised by a physician.
  • Manganese; calcium; copper; iron; antacids; soy; or antibiotics in the fluoroquinolone (such as, Cipro, Floxin) or tetracycline families: It may be advisable to separate your doses of zinc and these substances by at least 2 hours.
  • Penicillamine: Zinc interferes with penicillamine's absorption so it may be advisable to take zinc and penicillamine at least 2 hours apart.
  • Zinc supplements: You should also take extra copper and perhaps magnesium as well because zinc interferes with their absorption. Zinc interferes with iron absorption, too, but you shouldn't take iron supplements unless you know you are deficient.