The Impact of Nutritional Interventions beyond the First 2 Years of Life on Linear Growth: A Systematic Review and Meta-Analysis

Abstract

A large body of evidence suggests that the first 1000 d from conception 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 of age. The aim of this analysis was to evaluate the effectiveness of several nutrition-based interventions, specifically iron, zinc, calcium, iodine, vitamin A, multiple (≥2) micronutrients, protein, and food, at improving growth in children ≥2 y of age. A systematic search of MEDLINE and EMBASE retrieved 7794 articles. A total of 69 studies met prespecified inclusion criteria. Baseline height-for-age z score, age, nutrient dose, and study duration 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 micronutrients (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 height-for-age z score as a significant inverse predictor of the effect size. Iron, calcium, iodine, and food-based interventions had no significant effect on growth. Age at baseline, study duration, and dose were not related to effect size for any nutrient examined. These findings suggest that zinc, vitamin A, multiple micronutrients, 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.

Keywords: 1000 days; calcium; iron; multiple micronutrient; protein; stunting; vitamin A; zinc.

FIGURE 1

Flowchart illustrating the selection of trials for inclusion in the systematic review and meta-analysis. RCT, randomized controlled trial.

FIGURE 2

Forest plots of the effect on linear growth of single micronutrient interventions in children ≥2 y of age. Data derived from systematic literature review of nutrient interventions administered after age 2 y. (A) Iron. (B) Zinc. (C) Calcium. (D) Iodine. (E) Vitamin A. Fixed, fixed-effects model; IV, inverse variance; random, random-effects model; std., standard.

FIGURE 3

Relation between potential sources of heterogeneity and the standard mean effect of zinc intervention on linear growth in children ≥2 y of age. (A) Baseline HAZ was a significant predictor of the effect size (r = −0.51; P < 0.05). (B) Age (r = 0.17; P > 0.05), (C) study duration (r = −0.11; P > 0.05), (D) dose (r = 0.09; P > 0.05), and (E) serum zinc (r = 0.19; P > 0.05) were not predictors of the effect size. Each point represents one study estimate. HAZ, height-for-age z score.

FIGURE 4

Forest plots of the effect on linear growth of multiple-micronutrient, protein, and food-based interventions in children ≥2 y of age. Data derived from systematic literature review of nutrient interventions administered after age 2 y. (A) Multiple micronutrient. (B) Protein. (C) Food-based. Fixed, fixed-effects model; IV, inverse variance; MM, multiple micronutrient; random, random-effects model; std., standard.

FIGURE 5

Relation between potential sources of heterogeneity and the standard mean effect of multiple-micronutrient interventions on linear growth in children ≥2 y of age. (A) Baseline HAZ was a significant predictor of the effect size (r = −0.60; P < 0.05). (B) Age (r = 0.45; P > 0.05) and (C) study duration (r = −0.14; P > 0.05) were not predictors of the effect size. Each point represents 1 study estimate. HAZ, height-for-age z score.

FIGURE 6

Relation between potential sources of heterogeneity and the standard mean effect of protein interventions on linear growth in children ≥2 y of age. (A) Baseline HAZ was a significant predictor of the effect size (r = −0.80; P < 0.05). (B) Age (r = −0.02; P > 0.05) and (C) study duration (r = −0.29; P > 0.05) were not predictors of the effect size. Each point represents 1 study estimate. HAZ, height-for-age z score.