Zinc is fast becoming recognised as a very important nutrient involved in a wide range of metabolic processes which become disturbed in many diseases. Despite the fact that there are many thousands of published papers indicating the clinical importance of zinc, only a handful of clinicians are applying the knowledge that is available.
We now know a lot about the deficiency effects, the role of zinc in enzyme function, dietary requirements and the toxic effects of zinc. However, there’s a lot to learn about interactions between zinc and other nutrients, things that affect individual requirements, zinc metabolism and peoples tolerance of excesses, not to mention the precise mechanisms by which a deficiency of zinc exerts its observable effects.
A lot of knowledge about zinc deficiency has come from animal studies, but a rare disease in children has also provided many useful clues. This condition is called acrodermatitis enteropathica, and it is caused by a hereditary absorption defect. Features include a loss of hair, skin troubles and diarrhoea. Symptoms start early in infancy, but only in formula fed babies. In the classical, untreated condition, such babies die from zinc deficiency. It was found that giving breast milk cured the condition because of the high levels of zinc it contains. Now, zinc supplements can be given and such babies thrive.
FOOD SOURCES
The best dietary sources of zinc are fresh oysters, ginger root, muscle meats such as lamb chops and steak, pecans, split peas, brazil nuts beef liver, non-fat dry milk, egg yolk, wholewheat, rye, oats, peanuts, lima beans, soy lecithin, almonds, walnuts, chicken, buckwheat, hazelnuts, clams, green peas, shrimps, turnips, parsley, potatoes, garlic, wholewheat bread, carrots, beans, raw milk, pork chops and corn.
DEFICENCY SYMPTOMS AND SIGNS
- Slow growth
- Infertility/delayed sexual maturation
- Low sperm count
- Hair loss
- Skin conditions of various kinds
- Diarrhoea
- Immune deficiencies
- Behavioural and sleep disturbances
- Night blindness
- Impaired taste or smell
- Impaired wound healing
- White spots on finger nails
The degree to which zinc deficiency contributes to a wide range of common clinical situations has not yet been thoroughly researched and evaluated. However, many physicians who asses the zinc status of their patients on a routine basis are aware of the number of patients whose problems respond well to zinc supplements.
CONDITIONS WHICH MAY OR CAN BE CAUSED BY ZINC DEFICENCY
- Frequent and/or sever infections
- Many skin problems
- Delayed wound healing and post-operative ‘complications’
- Congenital malformations
- Retardation of growth and/or sexual maturation
- Impotence, infertility and low sperm count, reduced sex drive
- Behavioural and sleep disturbances
- Psychiatric problems
- Dandruff, hair loss
- Impaired glucose tolerance
- Impaired taste, smell and dark-adaptation
- Connective tissue disease
- Gastrointestinal problems (diarrhoea)
Those who might have an inadequate dietary intake of zinc are:
- Those with anorexia nervosa, those on fad diets, and those on weight-reducing diets
- Those on exclusion diets for food allergies
- Strict vegetarians
- Those on restricted protein diets
- Those on synthetic diets (for the management of inborn errors of metabolism or malabsortion states)
- People who eat meat substitutes (soya ‘meat’ etc)
- The elderly
- Alcoholics
Some people eat enough but do not absorb it properly. These include:
- People on high-fibre diets (including lots of bran)
- Those taking iron tablets
- Children with acrodermatitis enteropathica
- People suffering from celiac disease
- People with achlorhydria and hypochlorhydria
- Those suffering from alcoholic cirrhosis
- People with pancreatic insufficiency
- The elderly
Some people lose zinc so need more. These include:
· People suffering from starvation, burns, diabetes mellitus
· Those taking diuretics
· Those taking the drug penicillamine
· Those with chronic blood loss or on dialysis (chronic renal disease)
· Those with exfoliative dermatitis, excessive sweating
· Sufferers from inflammatory bowel disease, intestinal parasites and hookworm
· Alcoholics
· People with liver disease (including viral hepatitis)
· Those with diarrhoeal fluid loss and ileostomy fluid loss
· After surgery or after trauma
Some people have increased needs for zinc because of the following conditions:
- Cancers
- Growth spurts and puberty
- Pregnancy and lactation
- Psoriasis
It has been suggested by many researchers that zinc in the household food supply in the UK and in the USA may well be inadequate. The refining of foods substantially reduces their zinc content and inadequate zinc intake may be much more widespread than is generally appreciated.
ZINC-NUTRIENT INTERACTIONS
The availability of zinc to the body’s cells is influenced by other nutrients, including iron, manganese, selenium and copper. Excess zinc inhabibits the absorption of copper and can lead to copper-deficit anaemia. Oral iron supplements can interfere with zinc absorption which is especially important in pregnant women.
Zinc is essential for the metabolism of vitamin A.
Protein intake influences zinc absorption – the higher the protein intake the higher the zinc requirement.
It has been known since 1934 that zinc is necessary for the growth of animals. Retardation of growth is an early and prominent feature in young animals experimentally deprived of zinc. Zinc is required for optimum growth recovery rates in children with malnutrition, and children with hereditary zinc deficiency disease acrodermatitis enteropathica have a poor growth-rate. The rate of increase in growth parallels zinc supplementation. Formula-fed infants do not grow as well as breast-fed infants. Zinc deficiency during pregnancy is also associated with lower birth weights.
ZINC AND LACTATION
It has now become clear that the availability of zinc from human milk is greater than from cows’ milk, soya milk, and combined formulae, and that more attention should be paid to the trace element level in infant formulae.
A woman’s zinc requirement increase during pregnancy and lactation and this should be borne in mind because her dietary zinc may be borderline or indeed inadequate at the best of times. One study measured the zinc content of the food that pregnant and lactating women were eating and found that the average daily intake of zinc was only forty-two per cent of the recommended daily allowance.
ZINC AND PREGNANCY
For many years it has been known from animal studies that zinc deficiency is associated with decreased fertility, increased rates of miscarriage and increased rates of congenital malformations.
Researchers from the University of California studied mice fed a diet moderately deficient in zinc from day seven of pregnancy until birth. Offspring of these mice showed depressed immune function through to six months of age. Also the second and third generations, all of which were fed the normal control diet, continued to show reduced immune competence, although not to the same degree as in the first generation.
Studies published in the British Journal of Obstetrics and Gynaecology failed to show any association between zinc deficiency and problems in pregnancy, but these studies used serum and hair zinc-levelswhich are very unreliable methods of assessing zinc status.
It appears that zinc deficiency during the last two thirds of pregnancy can alter the basic development of the immune system, and several researchers conclude the adequate dietary zinc is essential during both pregnancy and lactation to ensure the development of an intact immune system in the offspring.
It is clear that zinc is a critically element which must be available to the developing foetus, in adequate amounts, for normal development. It makes sense for all women of childbearing age to eat a diet which will provide an adequate amount of zinc. This is especially true for women who have already had one or more problem-pregnancies or babies.
ZINC AND IMMUNITY
Zinc deficient animals and children have an increased susceptibility to infections. It is now clear that zinc has a profound influence on immune responses.
Oral zinc supplementation has been shown to be beneficial on the immune responses of old people.
It seems, from the research available, that zinc deficiency could well play a part in the in the suppression of the immune system which is often observed following bereavement or viral infections such as glandular fever. Long-standing vaginal trichomoniasis responding to oral supplementation with zinc has also been reported.
A recent study has demonstrated that sucking zinc gluconate lozenges (containing 50mg of zinc) may reduce the duration of a common cold.
Acquired immune deficiency syndrome (AIDS) is another area where investigation of zinc status of sufferers and the effects of zinc supplementation may turn out to be highly profitable.
ZINC AND THE SPECIAL SENSES
There is a considerable amount of evidence which shows that zinc is an important factor in maintaining the integrity of the special senses.
Vision
It is clear that zinc is essential for maintaining normal vision, and night-blindness that is not due to vitamin A deficiency can respond to zinc supplementation.
Zinc deficiency has also been implicated in congenital foetal abnormalities involving the eye.
Taste
Animal and human studies and clinical observations in humans have shown a definite correlation between zinc deficiency and an impaired or disordered sense of taste, and zinc supplementation can correct this.
Abnormalities in the sense of taste in patients having regular kidneys dialysis have been shown to be reserved by oral zinc supplementation.
Smell
The power of smell has been reported to be diminished in zinc deficiency. Zinc supplementation in those with a loss of the sense of smell has led to mixed findings and it appears that an impairment of this sense is not a condition that consistently responds to zinc supplements.
ZINC AND REPRODUCTIVE FUNCTION
Zinc is necessary for the production of sperms, the developmentof primary and secondary sexual characteristics, and all phases of the reproductive process in the female form oestrus to birth and lactation.
Zinc deficiency has been clearly shown to be a cause of low sperm count and male infertility.
ZINC AND WOUND HEALING
Clinical observations in humans have shown that there is an association between low zinc and chronic ulceration from various causes. Several studies have found that zinc improves the healing rate of surgical wounds.
ZINC AND ACNE
Studies in Sweden and the UK have shown that zinc supplementation can be of benefit to acne.
ZINC AND HAIR LOSS
Zinc is well recognized as being involved in hair growth. Patients with acrodermatitis enteropathica lose their hair and hair loss has also been observed in zinc deprived animals.
Supplementation with a high dose of zinc has been shown to reverse hair loss in those with alopecia, with rapid restoration of dense, thick hair growth. It may well be worth considering zinc supplementation if you have patchy or total hair loss.
ZINC AND MUSCLE FUNCTION
Recent reports have shown that zinc depletion reduces muscle strength and endurance; this suggests that oral zinc supplementation would increase stamina by prolonging muscle contraction.
Two studies of athletes in training revealed lower levels of serum zinc compared with those controls. It is possible that increased sweating, increased blood volume, protein-rich diets and increased sweat losses could account for the lower levels. Anyone undergoing rigorous athletic training should be assessed for zinc deficiency and should take supplements where appropriate.
ZINC AND MENTAL FUNCTION
It has long been known that children with acrodermatitis enteropathica are mentally lethargic, have poor concentration and are sullen, schizoid, depressed, miserable, irritable and tearful, never smile or laugh, are difficult to soothe and not soothed by close bodily contact. The restoration of smiling after zinc supplementation is one of the earliest signs that acrodermatitis is under control. The mechanisms by which these changes are brought about is not understood.
Researchers in England found that patients recently admitted to a psychiatric hospital had low plasma magnesium and zinc when compared with controls.
Mentally retarded children who eat dirt have been shown to have low hair-zinc and elevated hair-copper when compared to those who do not. Researchers feel that such an evaluation would be valuable contribution towards better nutritional care of the mentally retarded.
One researcher has reported that babies waking one or more times at night between midnight and 7am improved their sleep pattern when given 12mg of elemental zinc and 0.925 mg of manganese. He also noted that the babies had an increased appetite, and a reduction in irritability, diarrhoea, skin rashes and pallor.
Anyone of any age who has a mental disturbance or a behaviour or sleep disorder should be examined for zinc deficiency and given a therapeutic trial of zinc if necessary.
ZINC AND RHEUMATOID ARTHRITIS
Low serum zinc has been recorded in a number of inflammatory conditions including rheumatoid arthritis. Researchers in Seattle gave a zinc supplement, three times daily, to some patients with chronic, active rheumatoid arthritis; others were given a placebo. Those on zinc supplementation for twelve weeks did better than did the placebo group and had marked improvement in joint swelling, morning stiffness, walking time, overall condition and joint tenderness, when compared with the control group.
ZINC AND INFLAMMATORY BOWEL DISEASE
It is well recognised that zinc is absorbed poorly in various malabsorbtion syndromes. What is less well known is that zinc deficiency is common in inflammatory bowel disease (Chron’s disease more than ulcuerative colitis), caused by impaired absorbtion, loss from the surface of the intestine, loss of zinc in the urine, poor appetite and poor food selection.
ZINC AND ALCOHOL
Poor nutrition and diuretic effect which results in more zinc being lost in the urine may both contribute to zinc deficiency in alcoholism. Alcoholics with zinc deficiency can develop an acrodermattis-like, zinc-responsive skin rash. Anyone who drinks a lot should be suspected of being zinc deficient.
There is a definitive relationship between alcohol consumption during pregnancy and foetal abnormalities. There is now considerable evidence for a link between zinc deficiency and alcohol intake in the mothers of these children. It seems likely that zinc deficiency promotes the teratogenic effect of alcohol, resulting in the series of congenital abnormalities that are now so well in foetal alcohol syndrome.
ZINC AND DRUGS
Anyone taking drugs should be aware that some of them influence zinc metabolism. Drugs which produce a depletion of zinc include penicillamine, steroids, ethanol, diuretics and excessive tea and coffee. Laxative abuse and fibre supplementation can also reduce zinc absorption. Serum zinc/copper ratios are reduced in women taking combined oral contraceptives. The anticonvulsant medication, valproic acid, has been show to bind zinc, and its teratogenicity and side-effects (anorexia, hair loss, liver toxicity etc.) could be related to drug-induced zinc deficiency.
As more becomes known about drug-nutrient interaction it is likely that other drugs will be recognized as interfering with normal zinc metabolism. On the other hand, it is likely that as an awareness of the role of zinc inadequacy plays in the cause of a range of clinical conditions, zinc supplementation and nutritional handling may complement or even replace some current drug regimes.
Anyone taking long-term steroids, penicillamine or diuretics, and all alcoholics, should have their zinc status regularly monitored and supplementation instituted where appropriate.
ZINC AND TOXIC METALS
Lead and cadmium both inhibit, amongst others, zinc-dependent enzymes. So, clearly, the toxicity of these elements is reduced in the presence of adequate zinc. In fact, zinc and vitamin C have been shown to reduce blood levels of these poisons in workers who make lead batteries. Lead and cadmium exert a more toxic effect in the presence of zinc deficiency. This is highly relevant when assessing the behavioural effects of these elements in children, when zinc supplementation should seriously considered.
ZINC AND ESSENTIAL FATTY ACIDS
Zinc is necessary for the correct metabolism of essential fatty acids and their conversion to prostaglandins – in fact many of the symptoms of essential fatty acid deficiency are mimicked by zinc deficiency.
ZINC SUPPLEMENTATION
Oral zinc supplementation is relatively safe and nontoxic. Most of the studies have been done using sulphate, but amino-chelated zinc, zinc orotate or zinc acetate, citrate and picolinate can be used. It is well known that supplementation with zinc can reduce copper absorption and cause copper deficiency in the long term. For this reason, zinc supplements should be taken before or after mealtimes by one hour to avoid interaction with dietary elements.
You can see from this study zinc is a very important element in the maintenance of health and in the treatment of a wide range of disorders. The best way to find out if you are zinc deficient is to take zinc and see if you get better.
EFFECTS OF FOOD ON ZINC ABSORBTION
Several foods seem to reduce the absorbtion of zinc and so should not be eaten at the same time as zinc supplements. These include soya protein isolates, soya-base milk feeds, coffee, cows’ milk, chese, hamburgers, celery, lemon, brown bread, iron supplements, wholewheat bread, high-fiber diet foods, bran.
There is evidence that someone who has a low zinc diet appears to absorb more efficiently whatever zinc there is in the diet.
Items which have been shown not to interfere with dietary zinc absorbtion include bacon, white toast and human milk. Nutritional supplements with a significant inorganic iron content, such as those often prescribed to pregnant women can also inhibit the uptake of zinc. There is no convincing evidence to date that zinc absorbtion is influenced by hormonal factors, but it has been shown that vitamin D enhances the absorbtion of zinc. There is no evidence that vitamin C influences zinc absorbtion.
Though zinc may be found in high concentrations in cows milk and soya-milk infant feeds, its most easily absorbed from breast milk.
