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Indian Pediatr 2010;47: 841-842 |
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Effect of Oral Zinc Supplementation on the
Growth of Preterm Infants |
Sunil Sazawal and Robert E Black
Department of International Health, Johns Hopkins
Bloomberg School of Public Health, 615, North Wolfe Street,
Room E8527, Baltimore, MD 21205, USA.
Email: [email protected]
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Preterm infants are at increased risk of
death, acute and long-term morbidity; often associated with nutritional
compromise and impaired growth. With about 13 million preterm babies born
each year worldwide, the burden is disproportionately concentrated in
Africa and Asia, where about 85% of all preterm births occur (31% and 54%,
respectively)(1). Preterm and low birth weight babies may have impaired
zinc status due to low body stores, limited capacity to absorb and retain
micronutrients coupled with increased endogenous losses associated with
organ immaturity, high nutrient demand to support catch-up growth, and
inadequate intakes because exclusive breastfeeding does not compensate for
increased demand due to prematurity. Preterm infants have high zinc
deficit and dietary requirements as 60% fetal zinc is acquired during
third trimester of pregnancy. Zinc deficiency has a negative effect on
endocrine system leading to growth failure among other clinical
manifestations.
In this issue of Indian Pediatrics, Islam and
colleagues report the findings of a double blind randomized controlled
trial evaluating the efficacy of oral zinc supplementation on the growth
of hospital born preterm infants in the Neonatal Special Care Unit of
Dhaka in Bangladesh(2). This is the first study carried out selectively
among preterm babies to evaluate the effect of zinc supplementation in a
developing country setting. In this study, 100 preterm infants (below 37
weeks of gestation) weighing between 1000 g and <2500 g were enrolled and
randomized to receive either zinc and multi-vitamin supplement (Group I;
n=50) or only multivitamin supplement (Group II; n=50) for 6
weeks. At enrollment, serum zinc levels were in the lower limit of the
normal range. The investigators concluded that zinc supplementation among
preterm babies for 6 weeks resulted in improved weight gain and linear
growth, enhanced serum zinc status and reduced incidence of diarrhea.
There were no significant side effects of the supplements. The limitations
of the study reported by authors included: infants were not followed up
actively on daily basis to check compliance, and a long-term follow-up was
not undertaken. However with observed change in plasma zinc concentration
and growth impact, compliance does seem to have been adequate.
Supplementation was given for shorter duration (6 weeks) whereas in the
previously conducted studies in preterm infants the average period of
supplementation was for 6 months (3,4). It would have been of interest to
evaluate sustainability of improved growth because shorter period of
supplementation may in fact be more pragmatic and achievable in routine
care.
So far only a few double blind randomized controlled
trials, three from developed country sett-ings(3-5), two of which were in
premature infants, and five from developing country settings(6-10), have
reported the effects of zinc supplementation
during the first months of life on growth of infants born prematurely or
small for their gestational age. The dose in these studies varied between
3 mg to 10 mg of zinc per day. Of the 3 studies conducted in developed
countries (Spain and Canada), 2 studies among preterm infants showed
positive effect on plasma zinc concentrations and linear growth(3,4) and 1
on LBW infants showed no effect(5). However, no significant effect on
weight gain was observed in any of these studies(3-5). The available
evidence for the effect of zinc supplementation on growth among low birth
weight infants from developing countries setting is from India (2
studies)(6,7), Bangladesh (1 study)(8), Chile (1 study)(9) and Brazil (1
study)(10). The duration of supplementation in these studies ranged from 4
weeks to 1 year and the dosage of zinc supplement varied between 3 mg to 5
mg per day in first 6 months of age and 10 mg of zinc per day for >6-12
months. Both short term (4-6 weeks)(8, 10) and long term (6 months-1
year)(6,7,9) zinc supplementation had a beneficial effect on weight gain.
However, only 2 long term supplementation studies conducted in India and
Chile documented a significant increase in length gain with zinc
supplementation(7,9). On the contrary, the largest RCT conducted on LBW
Indian infants concluded no beneficial effect on length and weight gain
with zinc supplementation given for a period of 1 year, although a
positive effect on plasma zinc concentration was observed(6). There are
bound to be physiological differences between the preterm births and
non-preterm small for gestational age births because the period available
for zinc accumulation during gestation is different. Therefore some of the
conflicting data regarding impact of zinc on growth in low birth weight
infants may be contributed by mixing low birth weight and preterm births.
Most of the studies that have evaluated impact in low birth weight infants
in developing countries have not reported gestational age due to
difficulty of ascertaining it and so would have recruited a variable
mixture of preterm births and small for gestational babies. In the light
of available evidence, the findings of the current study provide an
important piece of additional data, which needs further confirmation. If
replicated, zinc supplementation as an intervention to improve growth of
hospital born preterm infants in developing country settings would be an
inexpensive and easy intervention to scale up and even take to community
service delivery. Studies with adequate sample size, preferably
multicentre and with longer-term follow up are needed to confirm and
quantify the magnitude of the beneficial effect of zinc supplementation on
growth among preterm babies.
Competing interests: None stated.
Funding: None.
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