Zinc

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, its 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. Severe zinc deficiency can cause a major loss of immune function, and mild zinc deficiency might impair immunity slightly. For this reason, making sure to get enough zinc may help keep you from catching colds or other infections. But zinc may be helpful for colds in a completely different way, too, by directly interfering with viruses in the nose or throat. For this purpose, it is used either as a nasal spray or in the form of lozenges taken every 2 hours from the first sign of cold symptoms. Intriguing evidence suggests that zinc supplements may have other specific benefits as well, including helping stomach ulcers heal, relieving symptoms of rheumatoid arthritis, slightly improving acne symptoms, increasing sperm count, aiding recovery from anorexia nervosa, improving growth rate in children with sickle-cell disease, and preventing sickle-cell crisis (a serious condition in people with sickle-cell anemia).

Sources

The official U.S. 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, 11 mg (13 mg if 18 years old or younger)
     
  • Nursing women, 12 mg (14 mg if 18 years old or younger)
The average diet in the developed world commonly provides insufficient zinc, especially in women, adolescents, infants, and the elderly. Thus, it may be a wise idea to increase your intake of zinc on general principles.
Individuals with alcoholism, sickle-cell anemia, diabetes, or kidney disease are also thought to be at increased risk for zinc deficiency.
Various drugs may also inhibit zinc absorption, including captopril and possibly other ACE inhibitors, drugs which reduce stomach acid (including H2 blockers and proton pump inhibitors), and oral contraceptives. Certain nutrients may have the same effect, such as calcium, soy, manganese, copper, and iron. Contrary to previous reports, folate is not likely to significantly affect zinc absorption.
Thiazide diuretics (water pills) can cause excessive loss of zinc in the urine.
Oysters are by far the best food source of zinc—a single serving will give you about 10 times the recommended daily intake! Seeds and nuts, peas, whole wheat, rye, and oats are not nearly as high in zinc, but you can get about 3 mg per serving of these foods.
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 the product contains (so-called elemental zinc) and the total milligrams of the zinc product. All figures given in this article refer to the amount of actual zinc to take.

Dosages

For most purposes, zinc should simply be taken at the recommended daily requirements listed previously. For best absorption, zinc supplements should not be taken at the same time as high-fiber foods; however, many high-fiber foods provide zinc in themselves. When taking zinc long term it is advisable to take 1 to 3 mg of copper daily as well, because zinc supplements can cause copper deficiency. Zinc may also interfere with magnesium and iron absorption. For treatment of colds, much higher doses of zinc are used, although only for a short period of time. The usual dosage is 13 to 23 mg of zinc as zinc gluconate every 2 hours for a week or two (but no longer). 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 case of zinc nasal spray, in the nose). It appears that of the common forms of zinc, only zinc gluconate and zinc acetate have the required antiviral properties. Also, some sweeteners and flavorings used in lozenges can block zincs 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. Long-term use of relatively high-dose zinc (90 mg daily or more) has been tried for various conditions such as acne, sickle-cell anemia, and rheumatoid arthritis, but medical supervision is essential because of the risk of toxicity (see Safety Issues).

Uses

Good evidence suggests that if you take zinc lozenges every 2 hours at the beginning of a cold, you will recover much more quickly. One study suggests that zinc nasal spray may be even more effective. These methods supply a high dose of zinc for a short time, and are thought to work by directly interfering with viruses in the nose and throat. Zinc can also be taken at nutritional doses orally to improve immunity; however, this approach probably only works if you are deficient in zinc to begin with. Topical zinc may also be helpful for cold sores. Pregnant women should make sure to get enough zinc. One large double-blind study in zinc-deficient pregnant women found that a standard zinc supplement could significantly improve the birth weight and head size of their newborn children. However, zinc supplements failed to make any difference in another large double-blind study of pregnant women that did not specifically select zinc-deficient women. Evidence also suggests that zinc can reduce symptoms of acne, although most studies used high, possibly toxic, doses of zinc. Growing evidence suggests that zinc, especially in combination with antioxidants, can help slow the progression of macular degeneration. Zinc may also improve growth rate in children with sickle cell anemia and help prevent the development of sickle-cell crisis. Zinc might also speed the healing of stomach ulcers. Zinc has been tested as a treatment for rheumatoid arthritis with mixed results; overall, the evidence is not encouraging. Some, but not all, studies have found that HIV-positive individuals tend to be deficient in zinc, with levels dropping lower in more severe disease. 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. 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. However, other research has linked higher zinc intake to more rapid development of AIDS. The bottom line: If you have HIV, consult your physician before supplementing with zinc. Preliminary evidence from two small, double-blind trials suggests that zinc supplements might be helpful in treating anorexia nervosa, possibly enhancing weight gain and helping stabilize mood. One frequently quoted study often used to discredit the use of zinc in anorexia appears to be relatively meaningless when inspected closely. One small uncontrolled study found that zinc supplements increased sperm counts and improved fertility for men with low testosterone levels. But no such effect was seen in men whose testosterone levels were normal to begin with. Although the evidence that it works is not yet meaningful, zinc is sometimes recommended for the following conditions as well: Alzheimers disease, attention deficit disorder, benign prostatic hyperplasia, bladder infection, cataracts, diabetes, Downs syndrome, impotence, inflammatory bowel disease (ulcerative colitis and Crohns disease), osteoporosis,periodontal disease, prostatitis, psoriasis, tinnitus, and wound and burn healing. An 8-week double-blind trial of zinc at the somewhat high dose of 67 mg daily failed to find any benefit for eczema symptoms.

Scientific Evidence

Colds
Numerous studies have evaluated the effects of zinc lozenges or zinc nasal spray for colds. Most found positive results, as long as the right form of zinc is used (zinc gluconate or acetate).
In a double-blind placebo-controlled trial, 213 individuals with a newly starting cold used one squirt of zinc gluconate gel or placebo gel in each nostril every 4 hours while awake. The results were dramatic: Treated participants stayed sick an average of 2.3 days, while those receiving placebo were sick for an average of 9 days, a whopping 75% reduction in the duration of symptoms.
A more recent study found no benefits with zinc nasal spray. In this double-blind placebo-controlled trial, 185 individuals who had just started to develop cold symptoms were given either a zinc spray or placebo. No benefits were seen in the treated group as compared to the placebo group. However, this study used a much lower amount of zinc per squirt of spray than that of the positive study: 50 times lower to be exact. In addition, the spray contained zinc sulfate rather than zinc gluconate. The exact chemical form of zinc appears to markedly influence its ability to kill cold viruses (see below).
Zinc lozenges also appear to be helpful. 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 was just a placebo. 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.
Not all studies have shown such positive results. However, the overall results appear to be favorable. It has been suggested that the exact formulation of the zinc lozenge plays a significant role. Flavoring agents, such as citric acid and tartaric acid, appear to prevent zinc from inhibiting viruses, and chemical forms of zinc other than zinc gluconate or zinc acetate may not work. Sweeteners such as sorbitol, sucrose, dextrose, and mannitol are fine, but the information on glycine as a flavoring agent is equivocal.
Besides using zinc to directly interfere with viruses, supplementation at nutritional dosages may also help reduce the frequency of colds by strengthening your overall health.
In a 2-year study of nursing home residents, participants given zinc and selenium developed illnesses much less frequently than those given placebo. Of course, it isn't clear from this study which was more helpful, the zinc or the selenium. However, we do know that chronic zinc deficiency weakens the immune system, and studies performed in developing countries using zinc alone have found benefits. For example, a 6-month double-blind placebo-controlled study of 609 preschool children in India found that zinc supplementsreduced the rate of respiratory infections by 45%. Nine other studies have also found zinc supplements helpful for preventing illness.
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. 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.
Acne
Studies suggest that people with acne have lower-than-normal levels of zinc in their bodies. This fact alone does not prove that taking zinc supplements will help acne, but several small double-blind studies involving a total of over 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. Similar results have been seen in other studies using 90 to 135 mg of zinc daily. One study suggests that a lower and safer dose, 30 mg daily, may also be helpful. In some studies, however, no benefits were seen.
Two studies have compared zinc against a standard treatment for acne, the antibiotic tetracycline. One found that zinc was as effective as tetracycline taken at 250 mg daily, but another found the antibiotic far more effective when taken at 500 mg daily.
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.
Sickle-Cell Anemia
Children with sickle cell disease often do not grow normally. In a placebo-controlled study, 42 children with sickle cell disease (age 4 to 10) were given either zinc supplements (10 mg zinc daily) or placebo for a period of 1 year. Results showed that by the end of the study, the participants given zinc showed enhanced growth compared to those given placebo. It is not clear whether participants were actually deficient in zinc or simply benefited from the zinc supplement regardless of deficiency.
Unfortunately, (and inexplicably) this study does not appear to have been double-blind, which makes the results less than fully reliable.
Zinc may also be helpful in preventing "sickle-cell crisis" in individuals with sickle-cell anemia. A double-blind placebo-controlled study treated 145 sickle-cell subjects with either 220 mg of zinc sulfate 3 times daily or placebo. 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.
Warning: Sickle-cell anemia is far too serious a condition to self-treat, and the relatively high dosages of zinc used in this study should be taken only under the supervision of a doctor (see Safety Issues).
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. Participants were randomly assigned to receive one of the following: antioxidants (vitamin C 500 mg, vitamin E 400 IU, and beta-carotene 15 mg), 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.
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.
In addition, there is 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.

Safety Issues

Zinc 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.
However, long-term use of 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. The U.S. 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:
  • Infants 0–6 months, 4 mg 7–12 months, 5 mg
     
  • Children 1 to 3 years, 7 mg 4 to 8 years, 12 mg 9 to 13 years, 23 mg
     
  • Males and females 14 to 18 years, 34 mg 19 years and older, 40 mg
     
  • Pregnant or nursing women, 40 mg (34 mg if 18 years old or younger)
Use of zinc can interfere with the absorption of penicillamine antibiotics in the tetracycline or fluoroquinolone (Cipro, Floxin) families. The potassium-sparing diuretic amiloride was found to significantly reduce zinc excretion from the body. 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.

Interactions

If you are taking:
  • Medications that reduce stomach acid such as Zantac (ranitidine) or Prilosec (omeprazole); ACE inhibitors; oral contraceptives; estrogen-replacement therapy; thiazide diuretics; calcium; copper; or iron: You may need to take extra zinc.
     
  • Manganese, antacids, soy, or antibiotics in the fluoroquinolone (e.g.,Cipro, Floxin) or tetracycline families: It may be advisable to separate your doses of zinc and these substances by at least 2 hours.
     
  • 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.
     
  • Penicillamine: Zinc interferes with penicillamine's absorption so it may be advisable to take zinc and penicillamine at least 2 hours apart.
     
  • Amiloride: It 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.