Iron status and linear growth: a prospective study in school-age children

Abstract

Studies regarding the role of iron on linear growth have yielded heterogeneous results. Some trials indicate that iron supplementation of iron-replete infants leads to slower-length gain. However, little is known of the relation between iron status and linear growth in school-age children. We quantified plasma ferritin, mean corpuscular volume (MCV), and hemoglobin in 2714 children aged 5-12 years at recruitment into a cohort study. Height was measured periodically for a median of 30 months. Height-for-age Z-scores (HAZ) were calculated using the World Health Organization growth reference. Mixed effects models with restricted cubic splines were used to construct population HAZ-for-age growth curves for sex- and age-specific quartiles of each iron status indicator. Ferritin and MCV were each inversely related to attained HAZ among boys after the adjustment for baseline age, baseline body mass index-for-age Z-score and socioeconomic status. There was a decreasing monotonic relation between quartiles of ferritin and estimated change in HAZ from ages 6 to 14 years (P trend=0.001); boys in the 4th quartile experienced a HAZ change that was 0.46 Z lower than that of boys in the 1st quartile (P=0.0006). Similarly, we observed smaller HAZ change among boys in the highest quartile of MCV in comparison with those in the 1st quartile (P trend=0.001). Hemoglobin was not related to linear growth in boys. None of the iron-status indicators were associated with linear growth in girls. Higher iron status, as indicated by ferritin and MCV, is related to slower linear growth in iron-replete school-age boys.