Micronutrient Interactions: Impact on Child Health and ... - Idpas.org

Iron-zinc-copper <strong>Interactions</strong>
tabolism, but this issue has not been studied
extensively. The effects of iron deficiency on
copper absorption and metabolism have not
been studied extensively either, but the limited
data available do not indicate a pronounced
effect. As suggested above, zinc deficiency
may be common in the same populations
that are prone to iron deficiency. Zinc
deficiency does not appear to have any pronounced
effect on iron absorption or metabolism,
but some reports suggest that copper
absorption may increase when zinc status
is impaired, even if the deficiency is only
marginal (Polberger et al. 1996). There are
limited data supporting a high prevalence
of copper deficiency in less-developed countries;
however, infants fed milk-based diets
may have compromised copper status as a
result of the low copper concentration of
milk and dairy products (Levy et al. 1985).
Marginal copper status can affect iron absorption
and status and, consequently, the
outcome of iron supplementation and fortification
programs. Less is known about the
effects of low copper status on zinc absorption
and status.
Trace Element Ratios
Because high concentrations of one element
may interfere with the absorption of another
element, it is important to consider
the ratios between trace elements. For example,
breast milk contains iron and zinc at
a ratio of approximately 1:4 whereas ironfortified
milk (or formula) may have a ratio
of 12:1 (Lönnerdal et al. 1983). When considering
competition for absorptive pathways,
it should be recognized that the iron
concentration of the diet in fortification
programs may be increased 50–60 times (or
more) while the zinc concentration remains
unchanged.
Although not as pronounced, the ratio
of zinc to copper can also be raised consid-
erably by zinc fortification. To date, this is
largely confined to infant formulas, in which
the zinc-copper ratio can be as high as 70:1
whereas this ratio is approximately 5:1 in
breast milk (Lönnerdal et al. 1983). It can
be expected that zinc supplements will become
more commonly used and that more
diets will be fortified with zinc. Thus, it is
evident that zinc nutriture should be monitored
when iron is added to the diet and that
copper nutriture should be monitored
when iron or zinc is added to the diet.
Iron-zinc <strong>Interactions</strong>
Although iron and zinc do not form similar
coordination complexes in water solution
and were not believed to directly compete
for absorptive sites, Solomons and Jacob
(1981) showed that high levels of iron can
interfere with zinc uptake as measured by
changes in serum zinc after dosing (area
under the curve). The postprandial rise in
serum zinc after an oral dose of 25 mg zinc
in water solution was given to fasting subjects
was lower when 25 mg of iron
(iron:zinc, 1:1) was given with the zinc dose
than when zinc was given alone. Increasing
the iron dose to 50 (2:1 ratio) and 75 mg
(3:1 ratio) reduced zinc uptake even further.
The dose of zinc given was high so that a
measurable increase in plasma zinc would
occur, and it has been argued that pharmacological
amounts of zinc and iron were
used. However, when supplements of iron
and zinc are given to treat deficiencies, the
doses used are not very different from those
used by Solomons and Jacob (1981). In a
subsequent study we used a lower amount
of zinc, which was more similar to the zinc
content of a regular meal (2.6 mg), and zinc
radioisotope and whole-body counting to
measure zinc absorption (Sandström et al.
1985). At this zinc level, there was no difference
in zinc absorption when the iron-zinc
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