Zinc may also be beneficial in rheumatoid arthritis, for which it has been shown to reduce symptoms; in preventing dental caries by strengthening tooth enamel; and with symptoms of heart disease, where the zinc-copper ratio may be important. The use of zinc in cancer prevention and the support of patients with cancers such as Hodgkin's disease and leukemia has been the subject of some interest.

Zinc therapy can reduce cadmium toxicity from pollution or from cadmium in water or foods. Cadmium toxicity may aggravate hypertension, atherosclerosis, and heart disease and produce complications of hypertension or stroke.

Zinc with vitamin B6 has also been used in the nutritional treatment of schizophrenia and, given along with manganese, has been helpful in some cases of senility. Zinc treatment may help with the loss of taste sensation that comes especially with aging, which is often due to zinc deficiency, and it may help stimulate the taste for food in patients with anorexia nervosa. Menstrual irregularity and female sexual organ difficulties may have some relationship to zinc levels and be helped by zinc therapy, though copper may be more important for these areas in women.

Deficiency and toxicity: Zinc is fairly nontoxic, especially in amounts of less than 100-150 mg. of elemental zinc daily, though this much zinc is probably not really needed and may interfere with the assimilation of other minerals. Zinc salts such as gluconate or sulfate are commonly available in 220 mg. tablets or capsules, each providing 55 mg. of elemental zinc. Taking one of these two or three times daily may cause some gastrointestinal irritation, nausea, or diarrhea but is more likely to have positive effects. Excessive supplementation may cause some immune suppression, premature heartbeats, dizziness, drowsiness, increased sweating, muscular incoordination, alcohol intolerance, hallucinations, and anemia, some of which is due to copper deficiency. More than 2 grams of zinc taken in one dose will usually produce vomiting. If not, it will likely lead to other symptoms until the body clears the excess zinc. Luckily, only a certain amount of it will be absorbed.

Zinc may interfere with copper absorption, so taking regular zinc supplements without copper can cause copper deficiency. This will interfere with iron metabolism and possibly cause anemia, as copper and iron are important in red blood cell formation. We usually need supplemental copper and vitamin A to balance the effect of extra zinc. Some formulas, for example, Nutrilite's product, A plus Zinc, contain vitamin A and zinc together, which improves the effect of both; additional copper, about 2 mg., might also be supplemented daily, though at another time than the zinc.

• Diet—low in zinc or high in copper; high in fiber, phytates, clay, alcohol, or phosphates, all of which bind zinc in the intestines and reduce absorption; food grown in low-zinc soils.
  
• Aging—when zinc absorption and intake are often reduced.
  
• Pregnancy—when zinc needs are increased.
  
• Growth periods—infancy, especially with increased copper intake levels and for those on low-zinc formulas; puberty, especially in adolescent boys.
• Birth control pills—use of these increases copper levels and thus reduces zinc.
• Premenstrual symptoms—associated with low zinc.
• Increased copper intake—high copper intake in water, food, or supplements will reduce zinc.
• Fasting or starvation—causes zinc depletion and increases needs for zinc.
• Serious illness or injury—causes zinc depletion and increases needs due to tissue healing.
• Hospitalization—stress of illness or treatment, particularly intravenous therapy without zinc supplementation.
• Stress—increases zinc use and needs.
• Burns—increases needs for tissue healing and dealing with stress.
• Acute or chronic infections—greater requirements from stress and for healing.
• Surgery—increased requirements for dealing with stress and for healing.
• Alcoholism—often associated with low zinc intake and higher needs; alcohol flushes zinc from the liver, causing increased losses.
• Diuretic therapy—may cause extra zinc losses.
• Psoriasis—rapid skin activity may deplete zinc.
• Parasites—cause zinc depletion and poor absorption.
• Malabsorption—from pancreatic insufficiency or after gastrointestinal surgery.
• Cirrhosis—zinc levels may be half of normal.
• Renal disease—causes increased zinc
• Chronic disease—metabolic and debilitating disease such as cancer.
• Athletics—increased zinc losses in sweat.
• Cadmium toxicity—interferes with zinc absorption and utilization.