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| Zinc
Jump to: Functions : Dietary
Sources : Required Intakes : Meal
Plan
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Introduction
The
mineral zinc is present in every part of the body and has a wide range
of functions. It helps with the healing of wounds and is a
vital component
of many enzyme reactions. Zinc is vital for the healthy working of many
of the body's systems. It is particularly important for healthy skin
and is
essential for a healthy immune system and resistance to infection.
Functions
Zinc has a range of functions. It plays a crucial role in growth and
cell division where it is required for protein and DNA synthesis, in insulin
activity, in the metabolism of the ovaries and testes, and in liver function.
As a component of many enzymes, zinc is involved in the metabolism of proteins,
carbohydrates, lipids and energy.
Our body contains about 2-3g of zinc. There are no specific storage sites
known for zinc and so a regular supply in the diet is required. Zinc is
found in all parts of our body, 60% is found in muscle, 30% in bone and
about 5% in our skin. Particularly high concentrations are in the prostate
gland and semen. Men need more zinc than women because male semen contains
100 times more zinc than is found in the blood. The more sexually active
a man the more zinc he will require. The recommended amounts of zinc for
adult men are 1/3 higher than those for women.
The first signs of zinc deficiency are impairment of taste, a poor immune
response and skin problems. Other symptoms of zinc deficiency can include
hair loss, diarrhoea, fatigue, delayed wound healing, and decreased growth
rate and mental development in infants. It is thought that zinc supplementation
can help skin conditions such as acne and eczema, prostate problems, anorexia
nervosa, alcoholics and those suffering from trauma or post-surgery. It
is always better to seek the advice of an expert before dosing yourself
with supplements. If you choose to take a zinc supplement you should not
need more than the daily recommended amount unless medical advice says
otherwise.
Dietary Sources
Zinc is present in a wide variety of foods, particularly in association
with protein foods. A vegetarian diet often contains less zinc than a meat
based diet and so it is important for vegetarians to eat plenty of foods
that are rich in this vital mineral.
Good sources for vegetarians include dairy products, beans and lentils,
yeast, nuts, seeds and wholegrain cereals. Pumpkin seeds provide one of
the most concentrated vegetarian food sources of zinc.
Only 20% of the zinc present in the diet is actually absorbed by the
body. Dietary fibre and phytic acid, found in bran, wholegrain cereals,
pulses and nuts, inhibit zinc absorption. Phytic acid forms a highly insoluble
complex with zinc which the body cannot absorb. Cooking processes can reduce
the adverse effects of both phytic acid and dietary fibre on zinc absorption.
Baking can destroy over half the phytic acid in wholemeal bread. Zinc deficiency
occurs where a large part of the diet consists of unleavened bread, such
as Iran and other Middle East countries. High levels of the toxic mineral
cadmium can also prevent zinc absorption because these two minerals compete
for absorption. Conversely high levels of zinc in the diet can prevent
the absorption of cadmium. Various chemicals added to many processed foods
can also reduce zinc absorption eg phosphates, EDTA. A deficiency of zinc
in the diet means zinc absorption is improved.
Zinc is lost via the faeces, urine, hair, skin, sweat, semen and also
menstruation.
|
| Sources of zinc (single servings) |
| Good sources |
Fair sources |
Poor sources |
| Chickpeas (200g or 7oz) |
2.8mg |
Peanut butter (20g or 2/3oz) |
0.6mg |
Dried dates (15g or 1/2oz) |
0.04mg |
| Baked beans (225g or 8oz) |
1.6mg |
Peas, frozen/canned (80g or 2.5oz) |
0.6mg |
Butter (7g or 1/4oz) |
0.01mg |
| 1 Vegeburger (100g or 3.5oz) |
1.6mg |
3 Dried figs (60g or 2oz ) |
0.5mg |
Raisins & Sultanas (15g
or 1/2oz) |
0.01mg |
| Pumpkin seeds (20g or 2/3oz) |
1.3mg |
3 Brazil nuts (10g or 1/3oz) |
0.4mg |
. |
. |
| Muesli (60g or 2.25oz) |
1.3mg |
Potatoes, boiled (200g or 7oz) |
0.4mg |
. |
. |
| Cheddar cheese (30g or 1oz) |
1.2mg |
1 Orange (140g or 5oz) |
0.3mg |
. |
. |
| Tahini paste (20g or 2/3oz) |
1.1mg |
6 Almonds (10g or 1/3oz) |
0.3mg |
. |
. |
| 1 Fruit yoghurt (150g or 5.25oz) |
0.9mg |
. |
. |
. |
. |
| Dried yeast (10g or 1/3oz) |
0.8mg |
. |
. |
. |
. |
| Wholemeal bread (40g or 1.5oz) |
0.8mg |
. |
. |
. |
. |
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Required Intakes
The old Recommended Daily Amounts (RDAs) have now been replaced by the
term Reference Nutrient Intake (RNI). The RNI is the amount of nutrient which
is enough for at least 97% of the population. |
Reference Nutrient Intakes for Zinc, mg/day.
| Age |
RNI |
- |
Age |
RNI |
| 0 to 6 months |
4.0mg |
- |
Adult men |
9.5mg |
| 7 months to 3 yrs |
5.0mg |
- |
Adult women |
7.0mg |
| 4 to 6 yrs |
6.5mg |
- |
. |
. |
| 7 to 10 yrs |
7.0mg |
- |
Pregnant women |
7..0mg |
| 11 to 14 yrs |
9.0mg |
- |
Breast feeding women |
9.5 to 13mg |
|
| Pregnant women do need
extra zinc, but it is thought that demands are met by increased absorption
from the gut. Breast feeding mothers need extra zinc in their diet. Breast
milk contains over 2mg of zinc in the first four months and women need
an extra 6mg a day to cover these demands. Breast feeding women must
include a generous serving of at least one good source of zinc in their
diet each day.
The iron supplements routinely prescribed for pregnant women when
there is no sign of anaemia may compromise zinc status. This is because
the interactions between essential minerals are complex and too much
of one may cause an imbalance of another.
Excess zinc is toxic. Too much zinc will interfere with the metabolism
of other minerals in the body, particularly iron and copper. Symptoms
of zinc toxicity occur after ingestion of 2g of or more and include
nausea, vomiting and fever.
|
Meal
Plan
| Sample one day's meal plan to meet the RNI of 9.5mg
for an adult man. |
| Breakfast |
Lunch |
Evening meal |
| Bowl of muesli with milk |
1.32mg |
Baked beans (225g or 8oz) |
1.57mg |
Potatoes, boiled (200g or 7oz) |
0.4mg |
| 1 slice of toast |
0.8mg |
2 slices of toast |
1.6mg |
Peas (80g or 2.5oz) |
0.56mg |
| . |
. |
Cheese (30g or 1oz) (or Pumpkin seeds, 20g or 2/3oz) |
1.2mg |
1 Vegeburger (100g or 3.5oz) |
1.3mg |
| . |
. |
. |
. |
1 Fruit yoghurt |
0.94mg |
| Total zinc intake 9.69mg |
more meal plans |
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