Recent global estimates indicate that over a quarter of children under 5 years of age are stunted, and consequently are at an increased risk of dying and other adverse consequences throughout life (1-3). Zinc is known to play a critical role in biological processes including cell growth, differentiation and metabolism (4,5) and deficiency in this micronutrient restricts childhood growth and decreases resistance to infections, which contribute significantly to morbidity and mortality in young children (6-8). Although severe zinc deficiency is rare in humans, mild to moderate deficiency may be common, especially in populations with low consumption of zinc-rich animal-source foods and high intakes of foods rich in phytates, which inhibit zinc absorption (9). Mild to moderate deficiency may be difficult to diagnose, as signs and symptoms such as increased susceptibility to infections and growth retardation are shared with other nutrient deficiencies and childhood illnesses (7,8).

Despite some inconsistent results (possibly because of the challenges of measuring zinc status), meta-analyses of intervention studies in a variety of countries have demonstrated a positive association between zinc supplementation and linear growth in children (8,10). Analysis from one of the studies indicated that a dose of 10 mg zinc per day for 24 weeks led to a net a gain of 0.37 (±0.25) cm in height of children who received zinc supplements compared to those who did not (10). In addition, it appears that zinc supplementation may have a greater impact on growth in stunted compared to non-stunted children (5,10). Zinc supplementation alone shows greater effect on linear growth than when supplemented in combination with iron, possibly through interference with zinc absorption or bioavailability (10). Because of this, the impact of zinc supplementation in countries with ongoing programmes of iron-folic acid supplementation may be less certain.

Although zinc supplementation is considered to be safe (8,10) and has been recommended as an effective intervention to reduce morbidity associated with diarrhoea and lower respiratory infections in young children (8,12), the likely need for daily administration of zinc supplements presents a number of programmatic challenges. The main operational constraints to successful delivery of such supplements include procurement and distribution of supplements over an extended period of time; limited access to, and poor utilization of, health services by the target population; inadequate training and motivation of frontline health workers; inadequate counselling of target recipients or their caregivers; and low adherence by the intended beneficiaries (8,11).

In countries with known widespread zinc deficiencies and high levels of stunted children, preventive zinc supplementation has a small but significant positive effect on linear growth. The limited impact of zinc supplementation suggests that such an intervention should be part of more comprehensive efforts to improve the general nutritional status of children, particularly in the first two years of life (3,8,9,13). Interventions that promote exclusive breastfeeding and appropriate complementary feeding along with micronutrient supplementation and fortification of foods may reduce the risk of stunting and are expected to provide substantial nutritional benefit to young children (3,14).

References

1. UNICEF, WHO, World Bank. Levels and trends in child malnutrition. Joint child malnutrition estimates. Geneva: World Health Organization; 2012. (http://www.who.int/nutgrowthdb/estimates2012/en/)

2. UNICEF, WHO, World Bank. Global database on child growth and malnutrition. Estimated prevalence of stunted children preschool children with 95% confidence intervals. Geneva: World Health Organization; 2013. (http://www.who.int/nutgrowthdb/estimates2013/en/)

3. Ramakrishnan U, Nguyen P, Martorell R. Effects of micronutrients on growth of children under 5 y of age: meta-analyses of single and multiple nutrient interventions. American Journal of Clinical Nutrition. 2009; 89:191–203.

4. Prasad AS. Discovery of human zinc deficiency and studies in an experimental human model. American Journal of Clinical Nutrition. 1991; 53:403-12.

5. Brown KH, Peerson JM, Rivera J, Allen LH. Effect of supplemental zinc on the growth and serum zinc concentrations of prepubertal children: a meta-analysis of randomized controlled trials. American Journal of Clinical Nutrition. 2002; 75:1062-1071.

6. Friis H, Ndhlovu P, Mduluza T, Kaondera K, Sandström B, Michaelsen KF, et al. The impact of zinc supplementation on growth and body composition: a randomized, controlled trial among rural Zimbabwean schoolchildren. European Journal of Clinical Nutrition. 1997; 51:38-45.

7. de Benoist B, Darnton-Hill I, Davidsson L, Fontaine O, Hotz C. Conclusions of the Joint Report WHO/UNICEF/IAEA/IZINCG Interagency meeting on zinc status indicators: foreword. Food and Nutrition Bulletin. 2007; 28:S480-484.

8. Brown KH, Peerson JM, Baker SK, Hess SY. Preventive zinc supplementation among infants, preschoolers, and older prepubertal children. Food and Nutrition Bulletin. 2009; 30:(Suppl 1):S12-36.

9. Sanstead H. Zinc deficiency: a public health problem? American Journal of Diseases of Children. 1991; 145:853-9.

10. Imdad A, Bhutta ZA. Effect of preventive zinc supplementation on linear growth in children under 5 years of age in developing countries: a meta-analysis of studies for input to the lives saved tool. BioMed Central Public Health. 2011, 11(Suppl 3):S22.

11. Bhutta ZA, Das JK, Rizvi A, Gaffey MF, Walker N, Horton S, et al. Evidence-based interventions for improvement of maternal and child nutrition: what can be done and at what cost? Lancet. 2013; S0140-6736(13)60996-4.

12. Allen LH, Gillespie SR. What works? A review of the efficacy and effectiveness of nutrition interventions. Geneva: United Nations Administrative Committee on Coordination/Sub-Committee on Nutrition (ACC/SCN) and Manila: Asian Development Bank; 2001.

13. Black RE, Victora CG, Walker SP, Bhutta ZA, Christian P, de Onis M, et al. Maternal and child undernutrition and overweight in low-income and middle-income countries. Lancet. 2013; S0140-6736(13)60937-X.

14. Imdad A, Yakoob MY, Bhutta ZA. Impact of maternal education about complementary feeding and provision of complementary foods on child growth in developing countries. BioMed Central Public Health. 2011; 11(Suppl 3):S25.

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Conflict of interest statements were collected from all named authors and no conflicts were identified.