Zinc

Functions

Zinc has many important structural, catalytic and regulatory roles. Zinc is a critical factor in cell membrane stabilisation and also in the structure of proteins. Zinc is an important part of over 200 enzymes, involved in processes as diverse as protein digestion, carbohydrate metabolism, bone metabolism, protein synthesis, nucleic acid synthesis, eyesight dark adaptation, oxygen transport and protection from free radical damage. In regulatory terms, zinc has a role to play in cell signalling and gene-directed cell death. Zinc is also an integral part of proteins that regulate gene expression.

A healthy dietary intake of zinc is crucial to the growth and development of children. See Deficiency section of this fact sheet for more on this topic.

Role in Disease Prevention

Zinc and Immune Function

Zinc is an essential part of a healthy immune system. Consistent scientific research shows that low zinc status compromises immune function, leading to a greater susceptibility to infections, including diarrhoea infections.

Food Sources

The main sources of zinc in New Zealand and Australian diets are red meats, fish, poultry, dairy products and wholegrains. The zinc found in animal-derived foods such as red meat and poultry is more easily absorbed from food than the zinc in plant-derived foods. Zinc containing plant foods, such as cereals and legumes (e.g. beans, peas, lentils), contain compounds known as phytates that inhibit zinc absorption. If a diet is based largely on plant-based foods and includes minimal red meats then specific steps must be taken to ensure zinc status is maintained.

Vegetarian Diets and Zinc

Phytates found in plant foods such as legumes and cereal can inhibit the absorption of zinc from these foods. Strict vegetarians, who exclude all animal meats from their diet, may need to consume 50% more zinc than meat eaters in order to absorb the same amount of zinc.

Plant foods containing zinc and phytates can be prepared in a specific manner in order to reduce the effect of phytates on zinc absorption, as follows:

Fermentation to Reduce Phytates 

Fermentation of phytate containing foods breaks down the phytates, thereby allowing any contained zinc to be more easily absorbed from the food.

Soaking and Sprouting of Legumes to Reduce Phytates 

The level of phytates in legumes can be reduced by soaking them in water overnight and then disposing of the water, before cooking the legumes in fresh water. Sprouting of legumes can also reduce the amount of phytates in legumes.

Canned or Tinned Beans Contain Less Phytates

The canning process reduces phytate levels in beans, to a level even lower than that produced by soaking and rinsing raw beans (as described above). Canned legumes, therefore, provide a particularly useful dietary source of zinc for vegetarians and individuals who consume only limited amounts of animal meats.

Nutrient Interactions with Zinc - Iron, Copper,

Dietary supplements of iron (but not dietary levels of iron) can decrease zinc absorption. Large dietary supplements of zinc (over 50mg/day) for extended periods can interfere with the absorption of copper, another mineral required for good health. Consequently, individuals using mineral supplements should do so under the guidance of a health practitioner.

Typical Contributions from Food

Food	Zinc (mg)
Beef, sirloin steak, grilled (100g)	5.8
Beef, mince, fried (100g)	5.9
Lamb, leg steak, grilled (100g)	4.5
Pork, leg steak, grilled (100g)	3.4
Chicken breast, grilled (100g)	1.0
Snapper, flesh, baked (100g)	0.6
Pasta, fresh, cooked (1/2 cup)	1.1
Brown rice, boiled (1/2 cup)	0.7
Milk, trim, (1 cup)	1.6
Cheese, edam, (40g)	1.7
Yoghurt, fruit, low fat (1 cup)	0.9
Bread, white (1 medium slice)	0.2
Bread, wholemeal (1 medium slice)	0.4
Weetbix, breakfast cereal (2 biscuits)	0.8
Muesli, toasted, sweetened (1/2 cup)	1.6
Baked beans (1/2 cup)	0.6
Peas, green, frozen, boiled (1/2 cup)	0.6
Peas, split, boiled (1/2 cup)	3.4
Silverbeet, boiled (1/2 cup)	0.6

Source: The Concise New Zealand Food Composition Tables 7th Edition.

Recommended Dietary Intake (RDI)

Following are the recommended dietary intake (RDI) levels for New Zealand and Australia. 

Iron RDIs – New Zealand and Australia

Life Stage	Age	Males (mg/day)	Females (mg/day)
Children	1-3 yr	3	3
	4-8 yr	4	4
	9-13 yr	6	6
	14-18 yr	13	7
Adults	19 - 50 yr	14	8
	51+ yr	14	8
Pregnant	14-18 yr	-	10
	19+ yr	-	11
Breastfeeding	14-18 yr	-	11
	19+ yr	-	12

Suggested Dietary Target for Reducing Chronic Disease Risk

The New Zealand and Australian governments have not set a suggested dietary target (SDT) for iron intake.

Deficiency

Those groups most at risk of a zinc deficiency include vegetarians, people with malabsorptive disorders and chronic alcoholics.

Symptoms of a mild zinc deficiency include an impaired immune system. As a zinc deficiency worsens further symptoms such as impaired taste and appetite, hair loss, poor wound healing, dermatitis, night blindness and diarrhoea may appear.

Zinc deficiency can result in adverse pregnancy outcomes and the slowing or halting of growth and development of infants and children, specifically delayed sexual maturation.

Diagnosis of a Zinc Deficiency

Zinc deficiencies are difficult to diagnose as there is no single, reliable, measure of zinc status. Serum zinc levels are often used as an indicator, however these can return incorrect results particularly when in the case of a mild zinc deficiency. It is preferable to use multiple measures of zinc status such as serum zinc levels, in conjunction with an assessment of dietary intake, and a functional measure (taste test or enzyme activity). Taste acuity tests are one form of functional measure, however as taste acuity can be altered by many other medical conditions in addition to a zinc deficiency they should not be used in isolation to diagnose a deficiency.

Toxicity

The highest level of average daily intake of zinc for adults aged 19 years and over, that is believed to not cause any adverse health effects, is 40mg/day. There is no evidence of adverse effects as a result of naturally occurring zinc in foods. However, long-term intake of zinc supplementation can cause problems such as suppressing the immune system, reducing copper status and decreasing HDL (or 'good') cholesterol levels. Zinc supplementation can also interfere with copper absorption (see Nutrient Interactions above). It is prudent, therefore, to only take zinc supplementation under supervision and when a zinc deficiency has been appropriately diagnosed. 

References

Garrow JS, James WPT & Ralph A. (2000). Human Nutrition and Dietetics (10th Ed). London: Churchill Livingstone.

Heath A-L. 2009. Personal communication. University of Otago, Human Nutrition Department.

Ministry of Health. (2006). Nutrient reference values for Australia and New Zealand. Canberra: Commonwealth of Australia.

Last Updated: 17 April 2009

The material provided by Thinking Nutrition Ltd on this website is for information purposes only. It is not a substitute for appropriate health advice from a qualified medical practitioner.