Iron Deficiency and Physical Growth Predict Attainment of Walking but Not Crawling in Poorly Nourished Zanzibari Infants

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Abstract
Locomotion allows infants to explore their environment, promoting development in other domains. Motor progression involves biological systems and experiential factors. Nutritional deficiencies could interfere with systems involved in locomotion. This study examined the associations between height-for-age (HAZ), weight-for-height (WHZ) Z-scores and anemia-iron status on locomotion in 646 Zanzibari infants. Motor milestones were assessed by trained observers using a 14-item scale. Two mutually exclusive samples were created. The crawling sample (n = 167, 6–18 mo old) included infants that crawled only or did not crawl; the walking sample (n = 479, 9–18 mo old) included children that walked alone or did not walk alone. Of the crawling and walking samples, 82.6 and 83.9% respectively, were iron deficient and/or anemic (hemoglobin < 100 g/L; zinc protoporphyrin ≥ 90 μmol/mol heme). Stunting (HAZ less than –2) occurred in 30.5% of the crawling sample and 38.4% of the walking sample. Logistic regression models estimated the influence of factors on crawling vs. not crawling or walking vs. not walking. Two models were tested: 1) included sex, age, SES, HAZ and WHZ; 2) added anemia-iron status category to Model 1. HAZ improved the odds of crawling by 30%, but was not significant in either model. Model 2 fit the walking sample data best (P < 0.0001); an increase in HAZ doubled the odds of walking and nonanemic, noniron deficient children were 66% more likely to walk than those with anemia and/or iron deficiency. In this sample of poorly nourished infants, growth and anemia-iron status are significant predictors of walking, but not crawling.