Minerals and Trace Elements 211predictor of low birth weight, and low maternal zinc
intake has been associated with an approximately
twofold increased risk of low birth weight and
increased risk of preterm delivery in poor urban
women.
Toxicity
Gross acute zinc toxicity has been described following
the drinking of water that has been stored in galva-
nized containers or the use of such water for renal
dialysis. Symptoms include nausea, vomiting, and
fever, and are apparent after acute ingestion of 2 g or
more. The more subtle effects of moderately elevated
intakes, not uncommon in some populations, are of
greater concern, because they are not easily detected.
Prolonged intakes of supraphysiological intakes of
zinc (75–300 mg/day) have been associated with
impaired copper utilization (producing features such
as microcytic anemia and neutropenia), impaired
immune responses and a decline of high-density lipo-
proteins, but some have argued that even short-term
intakes of about 25–50 mg zinc/day may interfere
with the metabolism of both iron and copper. The US
Food and Nutrition Board reported that there was no
evidence of adverse effects from intake of naturally
occurring zinc in food; however, they derived a toler-
able UL of 40 mg/day for adults older than 19 years,
which applies to total zinc intake from food, water,
and supplements (including fortifi ed foods). Data on
reduced copper status in humans were used to derive
this UL for zinc. Using similar data but different
uncertainty factors, the UL for total zinc intake was
set at 25 mg/day in the EU.
Genetic diseases
Acrodermatitis enteropathica, a rare, inborn, auto-
somal recessive disease, is a disorder of primary zinc
malabsorption. It is characterized by alopecia; vesicu-
lar, pustular and/or eczematoid skin lesions, specifi -
cally of the mouth, face, hands, feet and groin; growth
retardation; mental apathy; diarrhea and secondary
malabsorption, defects in cellular and phagocytic
immune function; and intercurrent infections. The
disorder responds very well to zinc therapy.
Assessing status
Measurement of zinc in plasma or activities of zinc
metalloenzymes or peptides in blood are frequently
used to measure zinc status. They are not ideal indices,
however, as they are relatively resistant to changes in
dietary zinc and, moreover, metabolic conditions
unrelated to zinc status cause them to decline. The
development of zinc defi ciency is different from that
of many other nutrients because a functional reserve
or store of zinc does not seem to be available when
zinc intake is inadequate. Tissue zinc is conserved by
reduction or cessation of growth in growing organ-
isms or by decreased excretion in nongrowing organ-
isms. Depending on the degree of defi ciency, zinc
homeostasis can be re-established by adjusting growth
and excretion or, with a more severe defi ciency, further
metabolic changes occur, resulting in a negative zinc
balance and loss of tissue zinc.Requirements and dietary sources
The US RDA for zinc was based primarily on data
derived from metabolic balance studies. Such studies
are technically diffi cult to perform and it is uncertain
whether information from these studies refl ects
true requirements. A different approach, using the
factorial method, was proposed for estimates of zinc
requirements and future RDAs. Factorial calculations
to estimate zinc requirements require knowledge of
obligatory losses, tissue composition, and needs for
growth and tissue repair. Current RDAs for zinc (rec-
ommended by the US Food and Nutrition Board in
2001) are infants 2 mg [fi rst 6 months; this is an ade-
quate intake (AI) value], 3 mg (7–12 months), chil-
dren 3 and 5 mg (1–3 and 4–8 years, respectively),
teenage boys 8 and 11 mg (9–13 and 14–18 years,
respectively), adult men 11 mg (19 years and more),
teenage girls 8 and 9 mg (9–13 and 14–18 years,
respectively), adult women 8 mg (19 years and older),
pregnant women 13 and 11 mg (younger than 18
years and 19–50 years, respectively) and lactating
women 14 and 12 mg (younger than 18 years and
19–50 years, respectively).
The zinc content of some common foods is given
in Table 9.13, whereas Table 9.14 classifi es foods based
on zinc energy density. The bioavailability of zinc in
different foods varies widely, from 5% to 50%. Meat,
seafood (in particular oysters) and liver are good
sources of bioavailable zinc. It has been estimated that
approximately 70% of dietary zinc in the US diet is
provided by animal products. In meat products, the
zinc content to some extent follows the color of the
meat, so that the highest content, approximately
50 mg/kg, is found in lean red meat, at least twice that