Is breast milk iodine concentration an influential factor in growth‐ and obesity‐related hormones and infants' growth parameters?

Abstract

Iodine, a key constituent of thyroid hormones, plays an indirect role in prenatal and postnatal growth. This study aimed to investigate whether breast milk iodine concentration (BMIC) is associated with growth‐ and obesity‐related hormones and subsequently the infants' anthropometric measures. In present study conducted in Tehran (Iran), 94 lactating mothers and healthy infants who were exclusively breastfed were included. Concentrations of iodine, insulin‐like growth factor‐1 (IGF‐1), adiponectin (AD) and leptin (LP) were measured in breast milk samples collected during 3‐ to 5‐day postpartum. Anthropometric measures of infants were assessed at 6 months of life, and age‐ and sex‐specific z ‐score values were calculated using the World Health Organization growth standards. The median (interquartile range) iodine, IGF‐1, AD and LP concentrations were 232.5 (157.5–296.0) μg L −1 , 15.7 (11.9–21.1) ng ml −1 , 13.2 (5.1–29.8) mg L −1 and 1.16 (0.86–1.70) ng ml −1 in breast milk, respectively. No significant correlations were found between BMIC and IGF‐1, AD and LP concentrations during the first few days postpartum. In adjusted regression model, BMIC was positively associated with weight‐for‐length z score of infants. In the presence of IGF‐1, AD or LP, the coefficients of BMIC for weight‐for‐length z score of infants were β = .003 ( P = .021), β = .002 ( P = .028) or β = .003 ( P = .013), respectively. No other anthropometric measurements were associated with iodine or growth‐ and obesity‐related hormones in breast milk. Our findings indicate that BMIC is a potential contributor to infants' growth status, independent of IGF‐1, AD or LP concentrations in breast milk. The underlying mechanisms remain to be elucidated.

Human Milk Micronutrients and Child Growth and Body Composition in the First 2 years: A Systematic Review

“…In total, 9992 unique abstracts were identified, 1001 full texts were assessed, and 139 articles met inclusion criteria, of which 28 articles reported HM micronutrients [ [24] , [25] , [26] , [27] , [28] , [29] , [30] , [31] , [32] , [33] , [34] , [35] , [36] , [37] , [38] , [39] , [40] , [41] , [42] , [43] , [44] , [45] , [46] , [47] , [48] , [49] , [50] , [51] ] ( Figure 1 ). The main reasons for excluding articles were: no HM analytes of interest were reported ( n = 89); no infant anthropometrics or only birth anthropometrics were reported ( n = 512); or no associations between HM analytes and infant anthropometrics were reported ( n = 165).…”

“…Among the 28 included micronutrient articles ( Table 1 and Supplementary Table 3 ), 8 (29%) were published before 1998 [ 27 , 29 , 31 , 35 , 38 , 39 , 41 , 45 ]; 19 (67%) were published in 2010 or later [ 25 , 26 , 28 , 30 , [32] , [33] , [34] , 36 , 37 , 40 , [42] , [43] , [44] , [46] , [47] , [48] , [49] , [50] , [51] ]. These 28 articles represented 26 unique studies involving 2526 dyads; 17 studies were conducted in low- or middle-income countries (according to World Bank criteria) [ [24] , [25] , [26] , 30 , [32] , [33] , [34] , [36] , [37] , [38] , [39] , [41] , [42] , [43] , [44] , 46 , 48 , 49 ]. Five studies were conducted as diet interventions or maternal micronutrient trials [ 24 , 31 , 36 , 44 , 49 ].…”

“…Of the 28 publications, 7 were cross-sectional, and 21 were longitudinal ( Table 1 and Supplementary Table 3 ). Among the 21 longitudinal investigations, 17 sampled HM in the first 6 mo only [ 24 , [26] , [27] , [28] , 31 , 32 , 34 , 37 , [39] , [40] , [41] , [42] , [43] , 45 ]; 3 also sampled HM between 6 and 12 mo [ 29 , 30 , 35 ] ( Table 1 , Supplementary Table 3 , and Figure 3 ). Most studies measured HM analytes and infant anthropometrics concurrently [ [25] , [26] , [27] , 29 , 30 , [32] , [33] , [34] , [35] , [36] , [37] , [38] , [39] , [40] , [41] , 43 , 45 , 46 ].…”

“…Nazeri et al. [ 42 ] and Ellsworth et al. [ 28 ] each reported positive associations between HM iodine concentrations in the first 2 wk and infant WLZ between 2 wk and 1 y.…”

Optimizing Growth: The Case for Iodine

“…The groups showed no difference in growth parameters, however. Yet, in Iranian infants aged 6 months, breast milk iodine concentration was positively associated with weight-for-length z-scores [ 73 ]. In China, the lowest mean values of height-for-age z-scores and weight-for-age z-scores in infants aged under 6 months were found when maternal UIC was well below requirements [ 74 ].…”