Iron status of infants and their mothers prior to starting complementary feeding : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Nutrition and Dietetics, Massey University, Albany, New Zealand

Abstract

Background: Women and children are vulnerable to developing iron deficiency (ID) due to their high iron requirements. In infancy, ID may cause irreversible deficits in cognitive functioning as well as adversely impacting immune functioning, growth, and oxygen transport. The iron store accumulated in utero is estimated to be depleted by 4-6 months of age, at which time infants are at risk of ID if insufficient iron is supplied from complementary foods. While there has been much research on the iron status of infants over six months old, little is known about the iron status of younger infants, particularly in New Zealand. Maternal postpartum anaemia is associated with a reduced quality of life and can adversely affect the bond between mother and child. The postpartum period is considered a time of low ID risk and is an opportune time to replenish iron stores lost during pregnancy. However, international studies have shown that some women are not able to adequately replace these losses and remain ID throughout the first postpartum year. Despite this evidence, only one New Zealand study has investigated maternal iron status at six months postpartum. Additionally, while maternal and infant iron status is likely correlated during pregnancy and the newborn period, there is a paucity of evidence regarding the existence of a relationship at mid-infancy. Objectives: To determine the iron status of infants and mothers, to investigate the relationship between maternal and infant iron status and to determine the differences in infant iron status according to mode of milk feeding, prior to commencing complementary feeding. Methods: This study reports the baseline iron status of 133 mother-infant pairs from a randomised controlled trial. Term infants, 3-6 months of age who had not yet started complementary feeding, and their mothers, were included in the analysis. Haemoglobin (Hb) and serum ferritin (SF) were measured to determine iron status alongside the inflammatory marker, C-reactive protein. Infant anthropometric measures were taken, and demographic and dietary information was obtained via questionnaires. Pearson’s and Spearman’s rho correlations determined the relationship between maternal and infant iron status. One-way ANOVA and Kruskal-Wallis tests determined the differences in infant iron status according to mode of milk feeding. Results: Most infants (93.2%; SF ≥10 µg/L, Hb ≥110 g/L) and mothers (80.5%; SF ≥15 µg/L, Hb ≥120 g/L) were iron-replete. No infants had ID (SF <10 µg/L, Hb ≥110 g/L) or iron deficiency anaemia (SF <10 µg/L, Hb <110 g/L) but 6.8% had anaemia without ID (SF ≥10 µg/L, Hb <110 g/L). One mother had ID (0.8%; SF <15 µg/L, Hb ≥120 g/L), 9.8% had mild ID (SF <30 µg/L, Hb ≥120 g/L), 7.5% had SF ≥150 µg/L indicating iron overload and 1.5% had anaemia without ID (SF ≥15 µg/L, Hb <120 g/L). There was a weak positive relationship between maternal and infant serum ferritin (r=0.19, P(two-tailed)=0.03), however, no relationship between maternal and infant haemoglobin (P=0.91) was found. Infants fed breast milk only, infant formula only or mixed fed did not have significantly different serum ferritin (P=0.92) or haemoglobin (P=0.50) concentrations. Conclusion: Prior to starting complementary feeding, most mothers and their infants were iron-sufficient, and their iron stores were weakly correlated at 3-6 months postpartum. Additionally, infant iron status did not differ by the type of milk infants were fed. Future research should focus on understanding the complex relationship between maternal and infant iron status. Furthermore, the iron status of infants and mothers from diverse socioeconomic and ethnic backgrounds, as well as those experiencing food insecurity, should be investigated, as these groups have a greater risk of poor iron status.