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FOOD TODAY 05/2008

Zinc - a supernutrient?

Food TodayThe mineral zinc is ubiquitous in the body. Essential for core functions like digestion, reproduction and growth, zinc - which we can ingest via our food - is linked to the performance of many body systems. Its list of benefits is extensive and sometimes ambitious - can zinc really fight infection and heal wounds?

Found in every cell

Zinc is found in all plant and animal cells (and thus in our food). Zinc is needed for DNA (genetic material) synthesis and laying down new tissue, which makes it vital for proper growth and development in childhood. Zinc is an essential component of over 100 enzymes involved in the digestion and utilisation of fats, proteins and carbohydrates, and is intimately linked to energy production. Zinc also supports the immune system and this is why there has been considerable interest in its potential to fight infection and heal wounds.

HELPING US TO COMBAT INFECTION?

Zinc is required for the development of T-lymphocytes, the white blood cells in our body that attack viruses and harmful bacteria helping us combat infections. Studies show that in malnourished children with low zinc levels, zinc supplements boost the number of T-lymphocytes and reduce the severity and duration of infections.1 Based on this success, investigations have been underway for some years to see if zinc treatments like lozenges and nasal sprays are an effective alternative therapy for the common cold. A recent review of four large, well-designed studies found no therapeutic effect of zinc lozenges or nasal gel.2

Wound healing

Zinc supplements appear to be helpful in the treatment of skin problems like leg ulcers, but only in those who initially have low zinc levels. Zinc creams applied directly to a wound are more efficient than supplements at reducing infection and stimulating healing and zinc is now commonly found in acne creams and shampoos for scalp conditions to boost healing.3

Zinc in the diet

Zinc is found in a wide range of foods so consuming a varied diet is likely to provide an adequate zinc intake. This is around 7 mg per day for women and 9 mg per day for men. However, as red meat is one of the best sources of zinc, and phytates found in plant foods reduce the absorption of zinc, vegetarians must take particular care to include foods like dairy products, eggs, wholegrain cereals, nuts and pulses in their diet. Pregnant and breast-feeding women need an extra 2 mg/day to ensure an adequate supply for the growing baby, although this can be supplied easily by the extra food consumed.

   Selected Food Sources of Zinc

 Food Zinc (mg/100 g)
 Oysters, fresh  45 - 75 
 Clams  21 
 Wheatgerm, wheat bran  13 - 16 
 Brazil nuts  7 
 Meats, muscle  4.5 - 8.5 
 Parmesan cheese  4 
 Peas, dried  3.5 
 Hazelnuts  3.5 
 Egg, yolk  3.5 
 Peanuts  3 
 Sardines  3.5 
 Chicken, dark meat  2.85 
 Walnuts  2.25 
 Bread, wholewheat  1.65 
 Chickpeas  1.4 
 Shrimp or Prawns  1.15 
 Egg, whole  1.1 
 Milk  0.75 

 


Too much of a good thing

Accidental intakes of zinc of over 200 mg are highly toxic and will cause vomiting and sickness, whereas prolonged supplementation may interfere with the absorption of copper and iron. This is because copper, iron and zinc compete for the same pathway to get from the gut into the bloodstream; an excess intake of one mineral will upset absorption of the others.

Optimum intakes

In Europe most people get adequate zinc from a varied, balanced diet and need for supplementation is rare.4 Overt symptoms of deficiency like poor growth in children, impotence and skin lesions are rare but if zinc deficiency is suspected it is important to seek medical advice. As a general rule, a balanced diet is sufficient to provide all nutrients, and supplements are only useful if you are not getting enough nutrients from your diet (e.g. inadequate caloric intake, alcoholism, digestive disease).

References

  1. Black R.E. (1998). Therapeutic and preventive effects of zinc on serious childhood infectious diseases in developing countries. American Journal of Clinical Nutrition 68:476S-479S
  2. Caruso T.J. et al. (2007). Treatment of naturally acquired common colds with zinc: a structured review. Clinical Infectious Diseases 45:569-574
  3. Lansdown A.B. et al. (2007). Zinc in wound healing: theoretical, experimental and clinical aspects. Wound Repair and Regeneration 15:2-16
  4. Wuehler S.E. et al. (2005). Use of national food balance data to estimate the adequacy of zinc in national food supplies: methodology and regional estimates. Public Health Nutrition 8:812-819
Terms used in this article
Carbohydrates
Enzymes
Gel
Genetic
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