Zinc is considered one of the most important of the many nutrients needed for proper immune function, People who are zinc deficient are much more likely to develop infections, and many researchers believe the decline in immune function in older people is due, at least in part, to deficiencies of zinc and other nutrients Muscle pain and wasting, heart problems important for proper immunity. In one study, zinc supplementation (220 mg twice a day for one month) increased the number of infection-fighting white blood cells in healthy people over the age of 70. There was no such improvement in a group that received no supplementation.
Another study also suggests that zinc gluconate can help to reduce symptoms of the common cold. Student volunteers who took 184 mg a day of zinc gluconate as lozenges got over their colds in about four days of treatment, while students taking placebo lozenges were ill for an average of nine days. Zinc seems to work against colds only when it dissolves in the mouth, researchers point out. High zinc levels in saliva apparently affect facial nerve endings, drying up a runny nose and preventing the cold virus from multiplying.
Blood levels of zinc have been found to be low in people with AIDS; researchers are currently looking at whether zinc supplementation can help maintain their immunity.
Q. What role does zinc play in the body?
A. Zinc is known to be involved in the structure and function of cell membranes and in the production of more than 200 enzymes, including those involved in the production of nucleic acid, the cell's genetic material. And it's known to be essential for proper wound healing and healthy skin, for a strong immune system, for normal taste and smell and sexual function, for bone metabolism and for vision, among other things.
People who are zinc deficient often have a poor sense of taste and smell. This can create a vicious circle. The loss of taste and smell often leads to poor appetite, which in turn leads to poor nourishment.
In fact, some researchers believe that anorexia nervosa, a condition characterized by loss of appetite and compulsive dieting, may be aggravated when initial dieting leads to zinc deficiency. And one study found that increasing the calorie intake of women suffering from anorexia nervosa - including providing them with a balanced diet that incorporates the RNi of zinc - initially lowered their blood zinc levels. The researchers believed this was because the RN! of zinc (12 mg for women) did not provide all the zinc needed for the tissue-building that accompanied the weight gain. It took upwards of 75 mg of zinc supplementation, along with additional calories, for zinc blood levels to rise to normal in these women.
Q. Can zinc deficiency lead to loss of eyesight?
A Zinc is involved in normal functions of the retina (the light-sensitive membrane at the back of the eye). Degeneration of the central part of the retina, called macular degeneration, is a leading cause of vision loss in the elderly. In one study, healthy older people given 100 mg of zinc, twice a day, for one to two years had significantly less vision loss from macular degeneration than a similar group who were given placebos.
Q. Does zinc play a role in cancer prevention?
A. Findings are contradictory. Some studies indicate that adequate zinc intake protects against the development of cancer. In others, however, zinc-deficient animals actually had slower tumour growth than those with adequate intakes. Zinc may possibly help to protect against cancer by helping neutralize certain cancer-causing agents, such as cadmium, a heavy metal, and by keeping the immune system at optimum operating capacity. On the other hand, since zinc is necessary for normal cell growth, a deficiency might also slow down the growth of established cancer cells.
Since zinc deficiency leads to serious symptoms, however, induced zinc deficiency would never be used to treat cancer. For established cancer (in animals), this treatment has too many adverse side-effects to be used on humans. The same applies to some other minerals, too.
Q. What does zinc have to do with sexual function?
A. In men, zinc deficiency leads to a reduction in the production of testosterone, the main male hormone that stimulates the development of male reproductive organs, including the prostate, and the secondary sex characteristics, such as facial hair and muscles, Men with fertility problems who also have low blood levels of zinc often benefit from a course of zinc supplementation. Zinc deficiency also leads to reduced sex drive. Adolescent boys who are low in zinc often have delayed puberty.
Q. Isn't zinc sometimes used to treat prostate problems?
A. It has been used to treat the most common kind of prostate enlargement, called benign prostatic hyper-plasia. Although there is some anecdotal evidence that about 80 mg a day of zinc sulphate does help " men with this condition, there are no scientific studies to prove that it does, in fact, work.
Q. Anything else zinc is good for?
A. Zinc, like iron and other trace minerals, apparently plays a role in the body's production of neurotransmitters -brain chemicals that relay messages. In a study of people with head injuries, those who got about five times the amount of zinc normally found in intravenous formulas had significantly higher neurological scores, as assessed by a neurologist, a month after their accidents.
QUICK-REFERENCE GUIDE
RNI
Men: 15 mg Women: 12 mg
Sources
Good sources include oysters, beef, pork and beef liver, lamb, crab, wheat germ and miso (fermented soya bean paste).
Signs of Deficiency
Clinical deficiency is very rare. Effects are growth retardation, poor appetite, under-functioning sex glands, mental lethargy, delayed wound healing, abnormalities of taste, smell and vision, skin changes and increased susceptibility to infection.
Risks for Deficiency
Old age; reduced-calorie or vegetarian diets; use of diuretics; diabetes; alcohol abuse; excessive sweating.
Possible Toxicity Problems
Zinc competes with copper for intestinal absorption; some researchers believe that people taking amounts of zinc as low as 15 mg should also be getting about 2 mg of copper.
In a recent study, high doses of zinc depressed immune function. Even 25 mg of zinc, considered a fairly low dose, led to poorer immune function after six months of supplementation.
