Zinc functions in over 200 enzymatic reactions in the body.
METABOLISM
Zinc is involved in the synthesis and degradation of carbohydrates, lipids and proteins. It also helps detoxify alcohol.
IMMUNITY
Zinc is considered one of the most important nutrients for the immune system as it is necessary for healthy antibody, white blood cell, thymus gland and hormone function. It is therefore vital in maintaining resistance to infection and in wound healing.
HORMONES
Zinc is necessary for the secretion, synthesis and utilization of insulin. It also protects the insulin-producing pancreatic beta cells against destruction. Zinc is also involved in the metabolism of the pituitary, thyroid and adrenal glands, the ovaries and the testes. It is vital for healthy male sex hormone and prostate function.
TEETH AND BONE
Zinc is necessary for the maintenance of tooth structure and is present in the crystalline structure of bone and in bone enzymes.
SKIN
Normal skin function requires zinc. It is involved in local hormone activation, vitamin A binding protein formation, wound healing, inflammation control and tissue regeneration.
GROWTH
Zinc plays a key role in DNA synthesis and cell division and is therefore necessary for growth and repair of tissue. It is involved in the structure and function of cell membranes and collagen, bone, nail and hair growth, and protein synthesis.
PREGNANCY
Maternal zinc levels are linked to proper formation of the palate and lip, brain, eyes, heart, bones, lungs and urogenital system of the baby. Zinc plays an important role in normal growth, birthweight and completion of full term pregnancy.
BRAIN AND NERVOUS SYSTEM
Zinc is necessary for the production of brain neurotransmitters. Zinc metabolism abnormalities may play a role in the development of Alzheimer’s disease.
LIVER
Healthy liver function and release of vitamin A from the liver both require zinc.
OTHER FUNCTIONS
Zinc is also necessary for maintenance of vision, taste and smell and is the most abundant trace mineral in the eye. It is involved in the production of hydrochloric acid in the stomach and in the conversion of fatty acids to prostaglandins, which regulate body processes such as heart rate, blood pressure and the normal functioning of oil glands in the skin. Zinc is necessary for muscle contraction and maintaining acid-alkali balance.
INTERACTION WITH COPPER
Zinc and copper have related roles in many body functions and the balance between the two nutrients is important. Copper and zinc function together in the antioxidant enzyme copper-zinc superoxide dismutase. The ratio of zinc to copper appears to affect the levels of lipoproteins (fat carrying proteins) in the blood. Optimal zinc intake reduces total and harmful LDL cholesterol and raises beneficial HDL cholesterol levels. However, high levels of zinc (160 mg) have been shown to lower HDL cholesterol levels in blood, raise total and LDL cholesterol, induce platelet aggregation and lead to atherosclerosis in animals. These effects may be due to the lowering of copper levels. An imbalance in zinc and copper may be involved in high blood pressure.
On average, 20 per cent of zinc in food is absorbed although this depends on the source. Zinc from animal and fish sources is better absorbed than that from vegetables and fruits. High protein foods increase zinc absorption. Low zinc intakes lead to increased absorption.
High fiber diets can decrease zinc absorption as the phytic acid in cereals and vegetables binds zinc and reduces the amount available for absorption. Food additives and chemicals such as EDTA which are used in food processing can also reduce zinc absorption as can large amounts of textured vegetable protein. As Western diets shift away from red meat consumption and towards consumption of cereal proteins more cases of zinc deficiency may develop.
Zinc is combined in the intestines with picolinic acid which is secreted by the pancreas. This compound requires vitamin B6 for production. The zinc picolinate complex is transported across the absorptive cells of the intestine then to the liver where some is stored. Vitamin B6 deficiency or a decrease in pancreatic secretion, which is often seen in elderly people, will therefore affect zinc absorption.
Excretion of zinc is mainly via the feces but some is lost in the urine. Excessive sweating can cause losses of up to 3 mg per day.
Plasma or serum zinc levels may not reflect body stores. Red or white blood cell measures of zinc may be the most accurate way to assess body stores.
Symptoms of zinc deficiency include eczema on the face and hands, hair loss, mental apathy, defects in the reproductive organs, delayed sexual maturation, menstrual irregularities, decreased growth rate and impaired mental development. Deficiency may also lead to postnatal depression, loss of the senses of taste and smell, anemia, poor appetite, impaired conduction and nerve damage, white spots on the nails, mental disorders, susceptibility to infections, delayed wound healing and impotence in men.
Acrodermatitis enteropathica, a rare skin disease in infancy, is caused by a genetic inability to absorb zinc.
Alcoholic liver disease, trauma such as burns or surgery, viral hepatitis, diabetes and some kidney diseases cause larger than normal amounts of zinc to be excreted which can lead to deficiency. Athletes often have an increased need for zinc and are also at risk of deficiency.
A recent US study suggested that zinc intakes are declining. Those likely to have low intakes include infants, adolescents, women, older adults and those with lower levels of education and higher poverty levels. Preschool children and vegetarians may also be at risk.
PREGNANCY
Zinc deficiency in early pregnancy can lead to congenital birth defects, low birthweight, spontaneous abortion, premature delivery, mental retardation and behavior problems. Mothers with low zinc intakes may have babies who are more susceptible to infection.
EATING DISORDERS
Low levels of zinc have been found in sufferers of the eating disorder, anorexia nervosa. This complex disorder may be exacerbated by zinc deficiency. Initial dieting may lead to deficiency which in turn leads to poor senses of taste and smell and therefore poor appetite.
THE EYE
Zinc deficiency can lead to loss of eye function. Zinc deficiency may contribute to macular degeneration of the central part of the retina. It has been found that a zinc dependent enzyme necessary for eye function declines with age.
PERIODONTAL DISEASE
The severity of periodontal disease appears to be related to the level of zinc deficiency.
PREMENSTRUAL SYNDROME
The symptoms of premenstrual syndrome may be exacerbated by zinc deficiency. Researchers have found that zinc levels are lower in one phase of the menstrual cycle in PMS sufferers.
MALE SEXUAL FUNCtiON
Zinc levels are usually lower in infertile men leading to decreased testosterone levels and low sperm counts. Zinc deficiency in adolescence can delay puberty.
IMMUNE SYSTEM
Immune function is affected by zinc deficiency, which results in a decrease in the numbers of several types of T cells and natural killer cells and other components of the immune response. This leads to increased susceptibility to infection and may increase wound healing time.
CANCER
Zinc deficiency may play a role in the development of cancer. However, in some studies adequate zinc protects against the development of cancer and in others zinc deficiency actually slows tumor growth. Zinc is necessary for the maintenance of a healthy immune system but it is also necessary for tumor cells to grow.
BONES
Diets low in zinc may slow adolescent bone growth and increase the risk of osteoporosis later in life. Zinc excretion appears to be increased in osteoporosis sufferers.
Good sources of zinc include liver, shellfish, oysters, meat, canned fish, hard cheese, whole grains, nuts, eggs and pulses. Vegetables contain smaller amounts of zinc and also contain compounds which bind zinc, leaving less available for absorption.
The zinc in grains is found mainly in the germ and bran coverings so food refining and processing reduce the amount of zinc in food. For example, flour refining causes a 77 per cent loss in zinc, rice refining causes a loss of 83 per cent and processing cereals from whole grains causes an 80 per cent loss.
| Men | 15 mg |
| Women | 12 mg |
| Pregnancy | 15 mg |
| Lactation (first six months) | 19 mg |
| Lactation (second six months) | 16 mg |
Australia
| Men | 12 mg |
| Women | 12 mg |
| Pregnancy | add 4 mg |
| Lactation | add 6 mg |
UK
| Men | 9.5 mg |
| Women | 7 mg |
| Lactation | add 6 mg |
Zinc supplements are available in various forms such as zinc gluconate, zinc sulphate, zinc picolinate or chelated zinc. Zinc in the form of zinc picolinate may be the best supplement for use in those who do not secrete sufficient picolinate from the pancreas.
The elderly, vegetarians, pregnant and breast-feeding women, those recovering from illness or those with malabsorption disorders may benefit from zinc supplements. Zinc supplements have been shown to have beneficial effects when given to people whose zinc levels are below normal.
Zinc supplements may be best taken first thing in the morning or two hours after meals to avoid the inhibition of absorption by other food constituents. Zinc supplements should not be taken at the same time as medications which reduce zinc absorption. Zinc supplements taken on an empty stomach may cause nausea in some people.
If large amounts of zinc are taken regularly it may be necessary to supplement copper to avoid imbalance.
Toxic effects of zinc are rare as excessive absorption is usually prevented by vomiting. Doses over 50 mg may cause secondary deficiency of copper and very high doses (over 150 mg daily) may cause abdominal pain and vomiting. Other symptoms include dehydration, lethargy, anemia and dizziness.
High doses of zinc (150 to 450 mg daily) may suppress immune function, possibly by causing low white blood cell count and small red blood cells. Long term ingestion of high doses may also decrease levels of HDL cholesterol which can lead to heart disease.
Excessive use of supplements during pregnancy may be harmful for the fetus.
IMMUNE SYSTEM
Zinc supplementation improves immune function in those who are deficient. It increases the number of white blood cells and has been shown to inhibit the growth of bacteria and possibly viruses. In one recent study, lozenges containing zinc gluconate reduced the duration of the common cold and other studies suggest that zinc protects against colds. Oral supplementation with zinc has been used to treat herpes virus infection as has zinc sulfate gel.
Zinc can also be used to enhance wound healing. Taken before and after surgery, zinc supplements may speed recovery time.
PREGNANCY
Zinc supplementation in those who are deficient has been shown to improve birthweight and head circumference.
SKIN
Zinc is vital for normal skin function and has been used externally to treat acne, eczema, psoriasis and rosacea. The use of zinc supplements for the treatment of acne is controversial and the conflicting results may be due to the variation in the types of supplements used in different studies.
TASTE
Studies have shown that zinc may be of benefit as part of the therapy for anorexia nervosa by improving taste perception and sense of smell which occur as the disease progresses. Zinc has also been shown to improve taste perception in cancer patients undergoing radiation therapy which helps in the maintenance of normal weight and nutrient intake during treatment.
AIDS
Studies are being conducted to see whether zinc supplementation has any benefit in the treatment of AIDS. Some studies have shown improvement in immune function while others have not. A recent US study showed that zinc supplementation correlated with poorer survival.
DIABETES
Diabetics often excrete excess zinc in their urine and studies have shown beneficial effects of zinc supplementation. Zinc supplementation in animals improves glucose tolerance and in humans has been shown to improve glucose assimilation.
PROSTATE PROBLEMS
Zinc supplements may play a role in the treatment of benign prostatic hyperplasia (BPH), an enlargement of the prostate gland seen in 60 per cent of men between 40 and 59 years of age. Zinc treatment, in the form of zinc picolinate or zinc citrate, has been shown to reduce the enlargement of the prostate and to reduce the symptoms in most patients. The beneficial effects of zinc may be due to its involvement in hormonal metabolism. Zinc inhibits the conversion of testosterone to its more active form, which causes overproduction of prostate cells.
It also inhibits the binding of hormones to receptor cells. Zinc also acts to lower levels of another hormone, prolactin, which controls the uptake of testosterone into the prostate. Increasing zinc levels therefore restricts the actions of the hormones and leads to a reduction in prostate size.
MACULAR DEGENERATION
Zinc supplements have been used to treat age related macular degeneration, the leading cause of lack of vision in people aged over 55. In one study patients receiving 100 mg of zinc had significantly less vision loss.
DIGESTIVE DISEASES
Zinc supplementation appears to relieve symptoms of inflammatory bowel disease (IBD) such as reduced appetite, suppressed immunity and impaired taste. IBD patients may not be able to absorb zinc properly and oral supplementation does not always appear to improve symptoms. Intravenous zinc may be necessary. Zinc supplements have also been used in celiac disease.
OTHER USES
Zinc supplements have also been used to treat mild mental complaints, Alzheimer’s disease and to decrease blood fat levels.
Rheumatoid arthritis symptoms may be helped by zinc. Zinc levels appear to be low in arthritis sufferers and some studies have shown benefits of zinc sulfate treatment.
Topically administered zinc acts as an astringent and a weak antiseptic. It is also used in eye drops to treat eye inflammation and as a mouthwash to inhibit plaque growth and protect against tooth disease.
Zinc accompanies calcium in the mineralization of bone and is lost when calcium is lost from bone.
High iron intake can reduce zinc levels. High zinc intake can reduce iron absorption and encourage iron depletion from body storage. Phosphate salts can decrease the absorption of zinc. High blood copper content can depress zinc absorption from the intestine and high zinc intakes can reduce copper absorption.
Zinc deficiency appears to increase vitamin E requirements.
Thiazide diuretics, tetracyclines, penicillamine, caffeine and other drugs which bind zinc in the gut may reduce zinc absorption. Some anti-hypertensive drugs increase urinary loss of zinc. Alcohol interferes with zinc absorption and increases excretion. Contraceptive pills can lower blood levels of zinc.
Large amounts of zinc may impair copper absorption and reduce the ability to taste sweet and salt. If continued for long periods the secondary copper deficiency can lead to heart disease.