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The Impact of Nutritional Interventions on Linear Growth After 2 y of Life: a Systematic Review and Meta‐Analysis of Controlled Trials

A large body of evidence suggests that the first 1000 days is a critical window in which interventions to address malnutrition will be most effective, but little is known about the impact on linear growth of nutritional interventions in children ≥2 y. The aim of this analysis was to evaluate the effectiveness of several nutrition‐based interventions, specifically (1) iron; 2) zinc; 3) calcium; 4) iodine; 5) vitamin A; 6) multiple (≥2) micronutrients; 7) protein; and 8) food, at improving growth in healthy children ≥2 y. A systematic search of MEDLINE and EMBASE retrieved 7,794 articles. A total of 69 studies met pre‐specified inclusion criteria. Data were pooled using the generic inverse variance method and expressed as standard mean differences (SMD) with 95% confidence intervals (CIs). Analyses were first conducted using a fixed effects model. If significant heterogeneity was observed (P‐value <0.05, I2 statistic >50%), analyses were repeated assuming a random effects model. Baseline height for age z‐score (HAZ), age, nutrient dose, study duration, and nutritional status were examined as potential sources of heterogeneity. Zinc (mean effect size 0.15; 95% CI: 0.06, 0.24), vitamin A (0.05, 95% CI: 0.01, 0.09), multiple micronutrient (0.26; 95% CI: 0.13, 0.39), and protein (0.68; 95% CI: 0.30, 1.05) had significant positive effects on linear growth with baseline HAZ a significant inverse predictor of the effect size. Iron (0.10; 95% CI: −0.04, 0.24), calcium (0.03; 95% CI: −0.09, 0.14), iodine (0.07; 95% CI: −0.10, 0.25), and food‐based (0.19; 95% CI: −0.28, 0.66) interventions had no significant effect on growth. Age at baseline, study duration and dose were not related to effect size for any nutrient examined. Further restricting our analysis to study populations with baseline iron, calcium, and zinc deficiency did not alter our conclusions for each respective nutrient. Our study suggests that zinc, vitamin A, multiple micronutrient, and protein interventions delivered after 24 mo of age can have a positive effect on linear growth, especially in populations that have experienced growth failure.