Nutrition News for Africa
Abstract - October 15, 2006
A Ranz Prize Lecture by Rosalind S. Gibson entitled “Zinc:
the missing link in combating micronutrient malnutrition in
developing countries” was published in the Proceedings
of the Nutrition Society (2006), 65, 51-60.
Although zinc deficiency in humans was first described in
the 1960s, it is only in 2002 that it was included as a major
risk factor to the global and regional burden of disease,
when its numerous adverse consequences on human health were
recognized. In 2004, the World Health Organization(WHO)/UNICEF
included zinc supplements in their recommended treatment regimen
for acute diarrhea. However, there is still a lack of awareness
of the importance of zinc in human nutrition and there is
a lack of food composition values for zinc for local staple
foods from developing countries.
Importance of zinc for human health: Multiple
functions in the body are affected by zinc deficiency, including
physical growth, immune competence, reproductive function
and neuro-behavioral development. Randomized controlled trials
(RCT) have shown that a positive growth response to zinc supplementation
is more likely to be apparent among children with pre-existing
growth failure. In the last decade, several RCT among high-risk
groups such as infants, young children and pregnant women
have examined preventive effects of zinc supplements on several
other important health outcomes. For example, a pooled analysis
of zinc supplementation trials confirmed a preventive effect
of zinc in reducing the incidence of diarrheal infection and
of acute lower respiratory infection, with reductions in diarrhea
and pneumonia in infants and young children in developing
countries. Efficacy trials on the therapeutic effects of zinc
supplements on children in developing countries have shown
dramatic reductions in the duration of acute and persistent
diarrhea and severe acute lower respiratory infection, but
no therapeutic effects were noted with daily zinc supplements
for measles or malaria therapy. Results of the RCT on maternal
health and pregnancy outcomes have been inconsistent.
Etiology of zinc deficiency: Three major
factors are responsible for the development of zinc deficiency
in developing countries; Inadequate intakes of dietary zinc,
excessive losses, high physiological requirements.
Identifying the risk of zinc deficiency: The
WHO cut-off value that indicates when childhood growth stunting
is a public health problem can be used to indicate a high
risk of zinc deficiency at a national level. Use of this indicator
has been adopted by the International Zinc Nutrition Consultative
Group (IZiNCG). In addition, IZiNCG has developed a composite
index of the national risk of zinc deficiency based on combined
information on stunting rates and the adequacy of zinc in
the national food supply. Countries can apply this composite
index to establish the likely risk of zinc deficiency and
respond accordingly.
Intervention strategies: Ideally zinc should
be incorporated into pre-existing intervention programs designed
to combat vitamin A, iron, and iodine deficiencies. The cost
of adding zinc to a preexisting micronutrient supplement will
range from about US$0.05-0.19 per capita per year depending
on the age-group. To date, no routine, large-scale targeted
zinc supplementation program exists. Fortification is a cost-effective
method that can be used at the national level to prevent deficiency
of both zinc and other micronutrients. The additional cost
of adding zinc to a national iron fortification program at
a level ranging from 30mg zinc/kg flour to 70mg zinc/kg flour
is US$0.03-0.04 per capita per year. National fortification
of maize and/or wheat flour with zinc and other micronutrients
have already been implemented in Mexico, Indonesia and South
Africa.
Dietary modification or diversification is a more sustainable
long-term, economically-feasible and culturally acceptable
strategy that can be used to alleviate several micronutrient
deficiencies simultaneously. A combination of dietary strategies
involving increased consumption of animal-source foods and
phytate reduction is the preferred approach to enhance both
the content and bioavailability of zinc in the diets of rural
households in developing countries.
Future intervention strategies at the crop production level
include biofortification to increase the content and /or bioavailability
of zinc in staple food crops.
Moving from science to programs: Ultimately
the success of any approach for combating zinc deficiency
depends on political and policy leadership in countries and
a strong commitment to developing an acceptable equitable
and sustainable solution.
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