Contribution of iron status at birth to infant iron status at 9 months: data from a prospective maternal-infant birth cohort in China

BACKGROUND/OBJECTIVES: The contribution of iron status at birth to iron status in infancy is not known. We used a physiologic framework to evaluate how iron status at birth related to iron status at 9 months, taking iron needs and sources into account. SUBJECTS/METHODS: In a longitudinal birth cohort in China, iron status measures in cord blood and venous blood in infancy (9 months) and clinical data were prospectively collected in 545 healthy term maternal–infant dyads. We used structural equation modeling (SEM) to create a 9-month iron composite and to assess direct and indirect contributions of multiple influences on 9-month iron status. Logistic regression was used to calculate odds ratios (OR) for iron deficiency (ID), iron deficiency anemia (IDA), and anemia. RESULTS: Approximately 15% (78/523) of infants were born with cord SF<75 μg/l, suggesting fetal-neonatal ID. At 9 months, 34.8% (186/535) and 19.6% (105/535) of infants had ID and IDA, respectively. The following factors were independently associated with poorer 9-month iron status: higher cord zinc protoporphyrin/heme (ZPP/H) (adjusted estimate −0.18, P< 0.001) and serum transferrin receptor (sTfR) (−0.11, P=0.004), lower cord hemoglobin (Hb) (0.13, P=0.004), lower birth weight (0.15, P< 0.001), male sex (0.10, P=0.013), older age at testing (−0.26, P<0.001), higher 9-month weight (−0.12, P=0.006) and breastfeeding (0.38, P<0.001). Breastfeeding at 9 months showed the strongest association, adjusting for all other factors. Compared to formula-fed infants, the odds of IDA were 19.1 (95%CI: 6.92, 52.49, P< 0.001) and 3.6 (95%CI: 1.04, 12.50, P=0.043) times higher in breastfed and mixed-fed infants, respectively. CONCLUSIONS: Indicators of iron status at birth, postnatal iron needs, and iron sources independently related to iron status at 9 months. Sex was an additional factor. Public health policies to identify and protect infants at increased risk of ID should be prioritized.