Several double-blind trials indicate that zinc supplements reduce the severity of acne.^1,2,3,4 In one double-blind trial,⁵ though not in another,⁶ zinc was found to be as effective as oral antibiotic therapy. Doctors sometimes suggest that people with acne take 30 mg of zinc two or three times per day for a few months, then 30 mg per day thereafter. It often takes 12 weeks before any improvement is seen. Long-term zinc supplementation requires 1–2 mg of copper per day to prevent copper deficiency.

Zinc is a component of many enzymes, including some that are needed to repair wounds. Even a mild deficiency of zinc can interfere with optimal recovery from everyday tissue damage, as well as from more serious trauma.^7,8 One controlled trial found the healing time of a surgical wound was reduced by 43% with oral supplementation of 50 mg of zinc three times per day, in the form of zinc sulfate.⁹

Whether oral zinc helps tissue healing when no actual zinc deficiency exists is unclear,¹⁰ but doctors often recommend 30 mg of zinc per day for four to six weeks to aid in the healing of wounds. Topical zinc-containing treatments, on the other hand, have improved healing of skin wounds even when there is no deficiency.^11,12 Long-term oral zinc supplementation must be accompanied by copper supplementation to prevent a zinc-induced copper deficiency. Typically, if 30 mg of zinc are taken each day, it should be accompanied by 2 mg of copper. If 60 mg of zinc are used, it should be accompanied by 3 mg of copper each day.

In a double-blind study, supplementation with oral zinc, in the form of zinc sulfate, for two months resulted in complete disappearance of warts in 87% of people treated, whereas none of those receiving a placebo improved.¹³ The amount of zinc used was based on body weight, with a maximum of 135 mg per day. Similar results were seen in another double-blind study.¹⁴ These large amounts of zinc should be used under the supervision of a doctor. Side effects included nausea, vomiting, and mild abdominal pain.

In a double-blind study, supplementing with zinc (23 mg three times per day for three months) decreased the severity of rosacea by about 75%, whereas no improvement occurred in the placebo group. Mild gastrointestinal upset was reported by 12% of the people taking zinc, but no other significant side effects occurred.¹⁶ Long-term zinc supplementation should be accompanied by a copper supplement, in order to prevent zinc-induced copper deficiency.

Zinc plays an important role in tissue growth processes important for skin ulcer healing. One study reported that patients with pressure ulcers had lower blood levels of zinc and iron than did patients without pressure ulcers,¹⁷ and preliminary reports suggested zinc supplements could help some types of skin ulcer.¹⁸ Supplementation with 150 mg of zinc per day improved healing in a preliminary study of elderly patients suffering from chronic leg ulcers.¹⁹ Double-blind trials using 135 to 150 mg of zinc daily have shown improvement²⁰ only in patients with low blood zinc levels,²¹ and no improvement in leg ulcer healing.^22,23 A double-blind trial of 150 mg zinc per day in people with skin ulcers due to sickle cell anemia found that the healing rate was almost three times faster in the zinc group than in the placebo group after six months.²⁴ Lastly, a preliminary study of patients with skin ulcers due to leprosy found that 50 mg of zinc per day in addition to anti-leprosy medication resulted in complete healing in most patients within 6 to 12 weeks.²⁵ Long-term zinc supplementation at these levels should be accompanied by supplements of copper and perhaps calcium, iron, and magnesium. Large amounts of zinc (over 50 mg per day) should only be taken under the supervision of a doctor.

Topically applied zinc using zinc-containing bandages has improved healing of leg ulcers in double-blind studies of both zinc-deficient²⁶ and elderly individuals.²⁷ Most controlled comparison studies have reported that these bandages are no more effective than other bandages used in the conventional treatment of skin ulcers,^28,29 but one controlled trial found non-elastic zinc bandages superior to alginate dressings or zinc-containing elastic stockinettes.³⁰ Two controlled trials of zinc-containing tape for foot ulcers due to leprosy concluded that zinc tape was similarly effective, but more convenient than conventional dressings.^31,32

People with DH frequently have mild malabsorption (difficulty absorbing certain nutrients) associated with low stomach acid (hypochlorhydria) and inflammation of the stomach lining (atrophic gastritis).³³ Mild malabsorption may result in anemia³⁴ and nutritional deficiencies of iron, folic acid,^35,36vitamin B12,^37,34 and zinc.^39,35,36 More severe malabsorption may result in loss of bone mass.⁴² Additional subtle deficiencies of vitamins and minerals are possible, but have not been investigated. Therefore, some doctors recommend people with DH have their nutritional status checked regularly with laboratory studies. These doctors may also recommend multivitamin-mineral supplements and, to correct the low stomach acid, supplemental betaine HCl (a source of hydrochloric acid).

Zinc is a component of many enzymes, including some that are needed to repair wounds. Even a mild deficiency of zinc can interfere with optimal recovery from everyday tissue damage, as well as from more serious trauma.^40,41 One controlled trial found the healing time of a surgical wound was reduced by 43% with oral supplementation of 50 mg of zinc three times per day, in the form of zinc sulfate.⁴²

Whether oral zinc helps tissue healing when no actual zinc deficiency exists is unclear,⁴³ but doctors often recommend 30 mg of zinc per day for four to six weeks to aid in the healing of wounds. Topical zinc-containing treatments, on the other hand, have improved healing of skin wounds even when there is no deficiency.^44,45 Long-term oral zinc supplementation must be accompanied by copper supplementation to prevent a zinc-induced copper deficiency. Typically, if 30 mg of zinc are taken each day, it should be accompanied by 2 mg of copper. If 60 mg of zinc are used, it should be accompanied by 3 mg of copper each day.

Zinc is a component of many enzymes, including some that are needed to repair wounds. Even a mild deficiency of zinc can interfere with optimal recovery from everyday tissue damage as well as from more serious trauma.⁴⁶ Trace minerals, such as manganese, copper, and silicon are also known to be important in the biochemistry of tissue healing.^47,48,49,50 However, there have been no controlled studies of people with sprains or strains to explore the effect of deficiency of these minerals, or of oral supplementation, on the rate of healing.

Boswellia has anti-inflammatory properties that have been compared to those of the NSAIDs used by many for inflammatory conditions.⁵¹ Clinical trials have found that boswellia is more effective than a placebo for relieving pain and swelling and preventing loss of function in people with osteoarthritis.⁵² Boswellia has also been found to be as effective as the anti-inflammatory drug valdecoxib (Bextra). In addition, while the improvements occurred more slowly in the boswellia group than in the valdecoxib group, they persisted for a longer period of time after treatment was discontinued.⁵³ One clinical trial found that a combination of boswellia, ashwagandha, turmeric, and zinc effectively treated pain and stiffness associated with OA but did not improve joint health, according to X-rays of the affected joint.⁵⁴ Unlike NSAIDs, long-term use of boswellia does not lead to irritation or ulceration of the stomach.

Deficient zinc levels have been reported in people with RA.⁵⁵ Some trials have found that zinc reduced RA symptoms,⁵⁶ but others have not.^57,58 Some suggest that zinc might only help those who are zinc-deficient,⁵⁹ and, although there is no universally accepted test for zinc deficiency, some doctors check white-blood-cell zinc levels.

Zinc is also needed for the repair of damaged tissue and has protected against stomach ulceration in animal studies.⁶⁰ In Europe, zinc combined with acexamic acid, an anti-inflammatory substance, is used as a drug in the treatment of peptic ulcers.⁶¹ In a small controlled trial, high amounts of zinc accelerated the healing of gastric ulcers compared with placebo.⁶² Some doctors suspect that such an exceptionally high intake of zinc may be unnecessary, suggesting instead that people with ulcers wishing to take zinc supplements use only 25 to 50 mg of zinc per day. Even at these lower levels, 1 to 3 mg of copper per day must be taken to avoid copper deficiency that would otherwise be induced by the zinc supplementation.

The malabsorption that occurs in celiac disease can lead to multiple nutritional deficiencies. The most common nutritional problems in people with celiac disease include deficiencies of essential fatty acids, iron, vitamin D, vitamin K, calcium, magnesium, and folic acid.⁶³Zinc malabsorption also occurs frequently in celiac disease⁶⁴ and may result in zinc deficiency, even in people who are otherwise in remission.⁶⁵ People with newly diagnosed celiac disease should be assessed for nutritional deficiencies by a doctor. Celiac patients who have not yet completely recovered should supplement with a high-potency multivitamin-mineral. Some patients may require even higher amounts of some of these vitamins and minerals—an issue that should be discussed with their healthcare practitioner. Evidence of a nutrient deficiency in a celiac patient is a clear indication for supplementation with that nutrient.

After commencement of a gluten-free diet, overall nutritional status gradually improves. However, deficiencies of some nutrients may persist, even in people who are strictly avoiding gluten. For example, magnesium deficiency was found in 8 of 23 adults with celiac disease who had been following a gluten-free diet and were symptom-free. When these adults were supplemented with magnesium for two years, their bone mineral density increased significantly.⁶⁶

Experimental animal studies have shown that a zinc salt of the amino acid carnosine exerts significant protection against ulcer formation and promotes the healing of existing ulcers.^67,68 However, because zinc by itself has been shown to be helpful against peptic ulcer, it is not known how much of the beneficial effect was due to the carnosine.^69,70 Clinical studies in humans demonstrated that this compound can help eradicate H. pylori, an organism that has been linked to peptic ulcer and stomach cancer.⁷¹ The amount of the zinc carnosine complex used in research studies for eradication of H. pylori is 150 mg twice daily.

Crohn’s disease often leads to malabsorption. As a result, deficiencies of many nutrients are common. For this reason, it makes sense for people with Crohn’s disease to take a high potency multivitamin-mineral supplement. In particular, deficiencies in zinc, folic acid, vitamin B12, vitamin D, and iron have been reported.^72,73,74 Zinc, folic acid, and vitamin B12 are all needed to repair intestinal cells damaged by Crohn’s disease. Some doctors recommend 25 to 50 mg of zinc (balanced with 2 to 4 mg of copper), 800 mcg of folic acid, and 800 mcg of vitamin B12 daily. Iron status should be evaluated by a doctor before considering supplementation.

Zinc and vitamin A, nutrients that aid in healing, are commonly used to help people with peptic ulcers. For example, the ulcers of people taking 50 mg of zinc three times per day healed three times faster than those of people who took placebo.⁷⁵ Since some types of gastritis can progress to peptic ulcer, it is possible that taking it may be useful. Nevertheless, the research does not yet show that zinc specifically helps people with gastritis. The amount of zinc used in this study is very high compared with what most people take (15–40 mg per day). Even at these lower levels, it is necessary to take 1–3 mg of copper per day to avoid a zinc-induced copper deficiency.

Zinc preparations have been shown to inhibit the replication of herpes simplex in the test tube.⁷⁶ In one study, people with recurrent herpes simplex infections applied a zinc sulfate solution daily to the sores. After healing occurred, the frequency of applications was reduced to once a week for a month, then to twice a month. During an observation period of 16 to 23 months, none of these people experienced a recurrence of their cold sores.⁷⁷

Zinc oxide, the only commercially available form of zinc for topical application, is probably ineffective as a treatment for herpes simplex.⁷⁸ Other forms of topical zinc can be obtained by prescription, through a compounding pharmacist. However, because an excessive concentration of zinc may cause skin irritation, topical zinc should be used only with the supervision of a doctor knowledgeable in its use.

Zinc deficiency has also been linked with recurrent canker sores in preliminary studies⁷⁹ and in one case report.⁸⁰ A preliminary trial found that supplementation with up to 150 mg of zinc per day reduced recurrences of canker sores by 50 to 100%; participants who were zinc deficient experienced the most consistent benefit.⁸¹ However, a double-blind trial (that did not test people for zinc deficiency) did not find zinc supplements helpful for recurrent canker sores.⁸²

Bloodroot contains alkaloids, principally sanguinarine, that are sometimes used in toothpaste and other oral hygiene products because they inhibit oral bacteria.^83,84 Sanguinarine-containing toothpastes and mouth rinses should be used according to manufacturer’s directions. A six-month, double-blind trial found that use of a bloodroot and zinc toothpaste reduced gingivitis significantly better than placebo.⁸⁵ However, a similar study was unable to replicate these results.⁸⁶ Thus, at present, it is unknown who will respond to bloodroot toothpaste and who will not. Concerns also exist about the long-term safety of bloodroot.

Zinc preparations have been shown to inhibit the replication of herpes simplex in the test tube.⁸⁷ In one study, people with recurrent herpes simplex infections applied a zinc sulfate solution daily to the sores. After healing occurred, the frequency of applications was reduced to once a week for a month, then to twice a month. During an observation period of 16 to 23 months, none of these people experienced a recurrence of their cold sores.⁸⁸

Zinc oxide, the only commercially available form of zinc for topical application, is probably ineffective as a treatment for herpes simplex.⁸⁹ Other forms of topical zinc can be obtained by prescription, through a compounding pharmacist. However, because an excessive concentration of zinc may cause skin irritation, topical zinc should be used only with the supervision of a doctor knowledgeable in its use.

Marginal deficiencies of zinc result in immune function impairments.⁹⁰ In a double-blind study of healthy elderly people, supplementing with 45 mg of zinc per day for one year significantly reduced the frequency of infections.⁹¹ Some doctors recommend lower amounts of supplemental zinc for people experiencing recurrent infections, such as 25 mg per day for adults and even lower amounts for children (depending on body weight). Zinc lozenges have been found helpful in some studies for the common cold. Long-term zinc supplementation should in most cases be accompanied by a copper supplement in order to prevent zinc-induced copper deficiency.

Blood levels of both zinc⁹² and selenium⁹³ are frequently low in people with HIV infection. Zinc supplements (45 mg per day) have been shown to reduce the number of infections in people with AIDS.⁹⁴ Zinc supplementation (12 mg per day for women, 15 mg per day for men) also slowed the decline in immune function in HIV-infected adults with low blood levels of zinc.⁹⁵

Most,^98,99 but not all,¹⁰⁰ double-blind studies have shown that elderly people have better immune function and reduced infection rates when taking a multiple vitamin-mineral formula. In one double-blind trial, supplements of 100 mcg per day of selenium and 20 mg per day of zinc, with or without additional vitamin C, vitamin E, and beta-carotene, reduced infections in elderly people, though vitamins without minerals had no effect.¹⁰¹ Burn victims have also experienced fewer infections after receiving trace mineral supplements in double-blind research.¹⁰² These studies suggest that trace minerals may be the most important micronutrients for enhancing immunity and preventing infections in the elderly.

Zinc supplements have been reported to increase immune function.^103,104 This effect may be especially important in the elderly according to double-blind studies.^105,101 Some doctors recommend zinc supplements for people with recurrent infections, suggesting 25 mg per day for adults and lower amounts for children (depending on body weight). However, too much zinc (300 mg per day) has been reported to impair immune function.¹⁰⁷

While zinc lozenges have been shown to be effective for reducing the symptoms and duration of the common cold in some controlled studies, it is not clear whether this effect is due to an enhancement of immune function or to the direct effect of zinc on the viruses themselves.¹⁰⁸

Zinc is a mineral nutrient important for proper immune system function and wound healing.¹⁰⁸ One study found most surgery patients recovering at home had low dietary intakes of zinc.¹⁰⁹ Low blood levels of zinc have been reported in patients after lung surgery.^110,111 In one study this deficiency lasted for up to seven days after surgery and was associated with higher risk of pneumonia,¹¹⁰ while another study found an association between post-operative zinc deficiency and fatigue.¹¹¹ Poor post-operative wound healing is also more common in people with zinc deficiency.¹¹⁴ Zinc supplements given to patients before surgery prevented zinc deficiency in one study, but the effect of these supplements on post-surgical health was not evaluated.¹¹⁵

In a preliminary study, pregnant women who used a zinc-containing nutritional supplement in the three months before and after conception had a 36% decreased chance of having a baby with a neural tube defect, and women who had the highest dietary zinc intake (but took no vitamin supplement) had a 30% decreased risk.¹¹⁶

Zinc supplementation (20 mg per day) was reported to reduce the incidence of GH in one double-blind trial studying a group of low-income Hispanic pregnant women who were not zinc deficient.¹¹⁷

Zinc is important for normal pancreatic insulin production and release. Zinc deficiency is very common in people with type 2 diabetes and may be related to genetic susceptibility.¹¹⁸ In one study, zinc deficiency was present in 77% of subjects being treated with metformin (a widely used anti-diabetes drug) and 90% of subjects being treated with both metformin and glimepiride (another anti-diabetes drug).¹¹⁹ A growing body of evidence shows zinc supplementation may be helpful in preventing and treating type 2 diabetes, but only those with poor zinc status appear to benefit.¹²⁰

In a placebo-controlled trial that included 200 participants with prediabetes, average zinc levels were noted to be lower than normal and taking 20 mg of zinc per day for one year resulted in reduced blood glucose, cholesterol, and LDL-cholesterol levels, and improved the fasting response to glucose ingestion (glucose tolerance), measures of insulin resistance, and pancreatic cell function. Moreover, 25% of those in given placebo progressed to type 2 diabetes, while only 11% of those given zinc developed diabetes.¹²¹ Nevertheless, the relationship between zinc status and type 2 diabetes risk remains unclear, as some research has noted a correlation between higher blood zinc levels and increased diabetes risk.¹²²

A controlled trial in people with type 2 diabetes with urinary protein loss (a sign of diabetes-related kidney damage) found that adding 50 mg of zinc (as zinc sulphate) to their diabetes treatment for 12 weeks improved blood glucose and triglyceride levels and reduced urinary protein loss.¹²³ Studies have also shown that supplementing with a combination of melatonin (10 mg per day) plus zinc (50 mg per day [as zinc acetate]), can improve blood glucose and lipid levels and reduce urinary protein loss in people with type 2 diabetes.^124,125

Many doctors recommend that people with type 2 diabetes and low zinc levels supplement with 15 to 25 mg of zinc per day to normalize zinc levels. Taking high doses of supplemental zinc long term increases the risk of copper deficiency. Most multivitamin-mineral supplements provide adequate copper to prevent deficiency.

Research has shown that supplementing with chromium (200 mcg per day)¹²⁹ or magnesium (340 mg per day)¹³⁰ can prevent blood sugar levels from falling excessively in people with hypoglycemia. Niacinamide (vitamin B3) has also been found to be helpful for hypoglycemic people.¹³¹ Other nutrients, including vitamin C, vitamin E, zinc, copper, manganese, and vitamin B6, may help control blood sugar levels in diabetics.¹³² Since there are similarities in the way the body regulates high and low blood sugar levels, these nutrients might be helpful for hypoglycemia as well, although the amounts needed for that purpose are not known.

People with type 1 diabetes may be more likely to be zinc-deficient than their healthy counterparts. Low zinc status leads to impaired immune function and increased oxidative stress and has been linked to poorer glucose control.^133,134 Zinc supplements have been found to increase antioxidant capacity and reduce lipid peroxidation in people with type 1 diabetes.¹³⁵

Despite evidence that zinc may be beneficial in people with type 1 diabetes, some doctors remain skeptical of high doses due to one 1994 study in which zinc supplementation, at a dose of 50 mg per day for 28 days, increased glycosylation (glucose-induced protein damage).¹³⁶ This trial is hard to evaluate because zinc supplementation increases the life of blood cells and such an effect artificially increases the lab test results for glycosylation. In fact, laboratory studies suggest zinc can inhibit glycation.^137,138 Until this issue is resolved, those with type 1 diabetes should consult a doctor before considering high-dose supplementation with zinc.

Supplementation with zinc brings about complete remission in hereditary acrodermatitis enteropathica. Zinc supplements in the amount of 30 to 150 mg per day are used by people with this condition.¹³⁹ People with acrodermatitis enteropathica need to be monitored by a healthcare professional to ensure that their level of zinc supplementation is adequate and that the zinc supplements are not inducing a copper deficiency.

In a double-blind study, children with ADHD who received 15 mg of zinc per day for six weeks showed significantly greater behavioral improvement, compared with children who received a placebo.¹⁴⁰ This study was conducted in Iran, and zinc deficiency has been found to be quite common in certain parts of that country. It is not clear, therefore, to what extent the results of this study apply to children living in other countries.

Zinc is another mineral antioxidant nutrient that the immune system requires. Zinc deficiency results in lowered immune defenses, and zinc supplementation increases immune activity in people with certain illnesses.¹⁴¹ As with vitamin A, zinc levels have been observed to fall during the early stages of measles infection and to return to normal several days later.¹⁴² There is evidence that zinc supplements are helpful in specific viral infections,^143,144,145 but there are no data on the effect of zinc on childhood exanthemous infections.

Zinc supplements have also been reported to increase immune function.^146,147 As a result, some doctors recommend zinc supplements for people with recurrent ear infections, suggesting 25 mg per day for adults and lower amounts for children. For example, a 30-pound child might be given 5 mg of zinc per day while suffering from OM. Nonetheless, zinc supplementation has not been studied in people with ear infections.

Another group of doctors has reported good results using a combination of zinc, manganese, and vitamin B6 for people with Osgood-Schlatter disease; however, the amounts of these supplements were not mentioned in the report.¹⁴⁸ Most physicians would consider reasonable daily amounts of these nutrients for adolescents to be 15 mg of zinc, 5 to 10 mg of manganese, and 25 mg of vitamin B6. Larger amounts might be used with medical supervision.

Zinc deficiency leads to reduced numbers of sperm and impotence in men.¹⁴⁹ The correlation between blood levels of zinc and sperm quality remains controversial. Infertile men have been reported to have lower levels of zinc in their semen, than do men with normal fertility.¹⁵⁰ Similarly, men with normal sperm density tend to have higher amounts of zinc in their semen, than do men with low sperm counts.¹⁵¹ However, other studies have found that a high concentration of zinc in the semen is related to decreased sperm motility in infertile men.^152,153 A few studies have shown that oral zinc supplementation improves both sperm count^154,155 motility,^154,157 and the physical characteristics of sperm in some groups of infertile men.¹⁵⁸ For infertile men with low semen zinc levels, a preliminary trial found that zinc supplements (240 mg per day) increased sperm counts and possibly contributed to successful impregnation by 3 of the 11 men.¹⁵⁹ However, these studies all included small numbers of volunteers, and thus the impact of their conclusions is limited. In a controlled trial, 100 men with low sperm motility received either 57 mg of zinc twice daily or a placebo.¹⁶⁰ After three months, there was significant improvement in sperm quality, sperm count, sperm motility, and fertilizing capacity of the sperm. The ideal amount of supplemental zinc remains unknown, but some doctors recommend 30 mg two times per day. Long-term zinc supplementation requires 1–2 mg of copper per day to prevent copper deficiency.

Zinc supplements have been used to treat people who had both tinnitus and hearing loss (usually age-related). Of those who had initially low blood levels of zinc, about 25% experienced an improvement in tinnitus after taking zinc (90–150 mg per day for three to six months).¹⁶⁰ Such large amounts of zinc should be monitored by a doctor. Two controlled clinical trials^161,161 found no benefit from zinc supplementation (66 mg per day in one double-blind trial) in people with tinnitus. However, participants in these studies were not zinc deficient. Preliminary research suggests that zinc supplementation is only helpful for tinnitus in people who are zinc deficient.¹⁶³ A doctor can measure blood levels of zinc.

Zinc supplements have also been reported to increase immune function.^163,164 As a result, some doctors recommend zinc supplements for people with recurrent ear infections, suggesting 25 mg per day for adults and lower amounts for children. For example, a 30-pound child might be given 5 mg of zinc per day while suffering from OM. Nonetheless, zinc supplementation has not been studied in people with ear infections.

Dietary zinc deficiency is common, and a lack of zinc may reduce the activity of retinol dehydrogenase, an enzyme needed to help vitamin A work in the eye. Zinc helps night blindness in people who are zinc-deficient;¹⁶⁵ therefore, many physicians suggest 15 to 30 mg of zinc per day to support healthy vision. Because long-term zinc supplementation may reduce copper levels, 1 to 2 mg of copper per day (depending on the amount of zinc used) is usually recommended for people who are supplementing with zinc for more than a few weeks.

Two important enzymes in the retina that are needed for vision require zinc. In a double-blind trial, supplementation with 45 mg of zinc per day for one to two years significantly reduced the rate of visual loss in people with macular degeneration.¹⁶⁶ However, in another double-blind trial, supplementation with the same amount of zinc did not prevent vision loss among people with a particular type of macular degeneration (the exudative form).¹⁶⁷

Dietary zinc deficiency is common, and a lack of zinc may reduce the activity of retinol dehydrogenase, an enzyme needed to help vitamin A work in the eye. Zinc helps night blindness in people who are zinc-deficient;¹⁶⁸ therefore, many physicians suggest 15 to 30 mg of zinc per day to support healthy vision. Because long-term zinc supplementation may reduce copper levels, 1 to 2 mg of copper per day (depending on the amount of zinc used) is usually recommended for people who are supplementing with zinc for more than a few weeks.

Two important enzymes in the retina that are needed for vision require zinc. In a double-blind trial, supplementation with 45 mg of zinc per day for one to two years significantly reduced the rate of visual loss in people with macular degeneration.¹⁶⁹ However, in another double-blind trial, supplementation with the same amount of zinc did not prevent vision loss among people with a particular type of macular degeneration (the exudative form).¹⁷⁰

In a preliminary study, pregnant women who used a zinc-containing nutritional supplement in the three months before and after conception had a 36% decreased chance of having a baby with a neural tube defect, and women who had the highest dietary zinc intake (but took no vitamin supplement) had a 30% decreased risk.¹⁷¹

Prostatic secretions are known to contain a high concentration of zinc; that observation suggests that zinc plays a role in normal prostate function. In one preliminary study, 19 men with benign prostatic hyperplasia took 150 mg of zinc daily for two months, and then 50 to 100 mg daily. In 74% of the men, the prostate became smaller.¹⁷⁶ Because this study did not include a control group, improvements may have been due to a placebo effect. Zinc also reduced prostatic size in an animal study but only when given by local injection.¹⁷⁷ Although the research supporting the use of zinc is weak, many doctors recommend its use. Because supplementing with large amounts of zinc (such as 30 mg per day or more) may potentially lead to copper deficiency, most doctors recommend taking 2 to 3 mg of copper per day along with zinc.

In healthy men, prostatic secretions contain a significant amount of zinc, which has antibacterial activity and is a key factor in the natural resistance of the male urinary tract infection.^178,179 In CBP^{180,178,182,183} and NBP¹⁸⁴ these zinc levels are significantly reduced; however, it is not clear whether this indicates a predisposition to, or is the result of, prostatic infection.^180,186 Zinc supplements increased semen levels of zinc in men with NBP in one study,¹⁸⁴but not in another.¹⁸² While zinc supplements have been associated with improvement of benign prostatic hyperplasia (BPH), according to one preliminary report,¹⁸⁹ no research has examined their effectiveness for prostatitis. Nonetheless, many doctors of natural medicine recommend zinc for this condition.

Exercise increases zinc losses from the human body, and severe zinc deficiency can compromise muscle function.^186,187 Athletes who do not eat an optimal diet, especially those who are trying to control their weight or use fad diets while exercising strenuously, may become deficient in zinc to the extent that performance or health is compromised.^188,189 One double-blind trial in women found that 135 mg per day of zinc for two weeks improved one measure of muscle strength.¹⁹⁰ Whether these women were zinc deficient was not determined in this study. A double-blind study of male athletes with low blood levels of zinc found that 20 mg per day of zinc improved the flexibility of the red blood cells during exercise, which could benefit blood flow to the muscles.¹⁹¹ No other studies of the effects of zinc supplementation in exercising people have been done. A safe amount of zinc for long-term use is 20 to 40 mg per day along with 1 to 2 mg of copper. Higher amounts should be taken only under the supervision of a doctor.

One trial studying postmenopausal women combined hormone replacement therapy with magnesium (600 mg per day), calcium (500 mg per day), vitamin C, B vitamins, vitamin D, zinc, copper, manganese, boron, and other nutrients for an eight- to nine-month period.¹⁹² In addition, participants were told to avoid processed foods, limit protein intake, emphasize vegetable over animal protein, and limit consumption of salt, sugar, alcohol, coffee, tea, chocolate, and tobacco. Bone density increased a remarkable 11%, compared to only 0.7% in women receiving hormone replacement alone.

Levels of zinc in both blood and bone have been reported to be low in people with osteoporosis,¹⁹³ and urinary loss of zinc has been reported to be high.¹⁹⁴ In one trial, men consuming only 10 mg of zinc per day from food had almost twice the risk of osteoporotic fractures compared with those eating significantly higher levels of zinc in their diets.¹⁹⁵ Whether zinc supplementation protects against bone loss has not yet been proven, though in one trial, supplementation with several minerals including zinc and calcium was more effective than calcium by itself.¹⁹⁶ Many doctors recommend that people with osteoporosis, as well as those trying to protect themselves from this disease, supplement with 10 to 30 mg of zinc per day.

Laboratory animals with severe, experimentally induced zinc deficiency developed hypothyroidism, whereas moderate zinc deficiency did not affect thyroid function.¹⁹⁸ In a small study of healthy people, thyroid hormone (thyroxine) levels tended to be lower in those with lower blood levels of zinc. In people with low zinc, supplementing with zinc increased thyroxine levels.¹⁹⁹ One case has been reported of a woman with severe zinc deficiency (caused by the combination of alcoholism and malabsorption) who developed hypothyroidism that was corrected by supplementing with zinc.²⁰⁰ Although the typical Western diet is marginally low in zinc,²⁰¹ additional research is needed to determine whether zinc supplementation would be effective for preventing or correcting hypothyroidism.