Introduction to Human Nutrition

Minerals and Trace Elements 209

stances in the meal and on the iron status of the
individual.

Micronutrient interactions

The fact that serum copper has been found to be low
in some cases of iron defi ciency anemia suggests
that iron status has an effect on copper metabolism.
Copper defi ciency impinges on iron metabolism,
causing an anemia that does not respond to iron
supplementation. Interactions between iron and
copper seem to be owing to impaired utilization of
one in the absence of the other. As mentioned above,
calcium can inhibit iron absorption under certain cir-
cumstances. In aqueous solutions iron impairs zinc
absorption, but this interaction does not take place
when iron is added to an animal protein meal, indi-
cating different uptake mechanisms for solutions and
solid foods.

9.8 Zinc

The natural abundance of zinc in the Earth’s crust is
0.02%. The principal ores of zinc are sphalerite or
blende (sulfi de), smithsonite (carbonate), calamine
(silicate), and franklinite (zinc iron oxide). Zinc is
used to form numerous alloys with other metals.

Brass, nickel, silver, typewriter metal, commercial

bronze, spring brass, German silver, soft solder, and

aluminum solder are some of the more important

alloys. Large quantities of zinc are used to produce die

castings, used extensively by the automotive, electri-

cal, and hardware industries. Zinc is also extensively

used to galvanize other metals, such as iron to prevent

corrosion. Zinc oxide is widely used in the manufac-

ture of paints, rubber products, cosmetics, pharma-

ceuticals, fl oor coverings, plastics, printing inks, soap,

storage batteries, textiles, electrical equipment, and

other products. Zinc sulfi de is used in making lumi-

nous dials, X-ray and television screens, and fl uores-

cent lights. The chloride and chromate are also

important compounds. In biological systems zinc is

virtually always in the divalent (+2) state. Unlike iron,

zinc does not exhibit any direct redox chemistry.

Absorption, transport, and

tissue distribution

Zinc is ubiquitous in the body. It is the most abundant

intracellular trace element, with >95% of the body

zinc intracellular. An adult human contains about 2 g

of zinc, of which about 60% and 30% are in skeletal

muscle and bone, respectively, and 4–6% is present

in skin (Table 9.11). Zinc turnover in these tissues is

slow and, therefore, the zinc in these tissues is not

accessible at times of deprivation. Because zinc is

essential for the synthesis of lean tissue, it is while this

is occurring that it may become a limiting nutrient.

Although some zinc may be available in short-term

zinc deprivation from a mobile hepatic pool, it is

Table 9.10 Iron content of some common foods

Food source Description Fe content (mg/100 g)

Liver Raw, calf 8.0
Beef Lean (from six
different cuts)

2.1

Black (blood)
sausage

Fried 20.0

Chicken Raw, meat only 0.7
Cod, plaice, whiting Raw 0.3–1.0
Eggs Chicken, whole,
raw

1.9

Pulses Raw 0.6–11.1
Wheat fl our Whole fl our 3.9
Wheat fl our White fl our 1.5–2.0
Milk Cow’s (3.9, 1.6
and 0.1% fat)

0.05–0.06

Green leafy
vegetables

Raw 0.7–2.2

Rice Raw, white,
polished

0.5

Potatoes Raw 0.3–0.4

Data from Holland et al. (1995). Reproduced with permission from
HMSO.

Table 9.11 Approximate zinc content of major organs and tissues in

the adult man

Tissue Total Zn content (g)

Percentage of body

Zn (%)

Skeletal muscle 1.53 ~57

Bone 0.77 29

Skin 0.16 6

Liver 0.13 5

Brain 0.04 1.5

Kidneys 0.02 0.7

Heart 0.01 0.4

Hair <0.01 ~0.1

Blood (plasma) <0.01 ~0.1

Modifi ed from Mills CF, ed, Zinc in Human Biology, copyright 1998

with kind permission of Springer Science + Business Media.