Tehran University of Medical Sciences Journal of Family and Reproductive Health 1735-8949 19 3 2025 11 04 232 239 EN Pantea Nazeri Breastfeeding Research Center, Family Health Research Institute, Tehran University of Medical Sciences, Tehran, Iran Najmeh Hamzavi Zarghani Department of Pediatrics, Faculty of Medicine & Dentistry, College of Health Sciences, University of Alberta, Edmonton, AB, Canada Zhale Tahmasebinejad Nutrition and Endocrine Research Center, Research Institute for Endocrine Sciences, Shahid Beheshti University of Medical Sciences, Tehran, Iran Mohadese Dashtkoohi Maternal, Fetal and Neonatal Research Center, Family Health Research Institute, Tehran University of Medical Sciences, Tehran, Iran Mehdi Hedayati Cellular and Molecular Endocrine Research Center, Research Institute for Endocrine Molecular Biology, Research Institute for Endocrine Sciences, Shahid Beheshti University of Medical Sciences, Tehran, Iran Parvin Mirmiran Nutrition and Endocrine Research Center, Research Institute for Endocrine Sciences, Shahid Beheshti University of Medical Sciences, Tehran, Iran Mamak Shariat Maternal, Fetal and Neonatal Research Center, Family Health Research Institute, Tehran University of Medical Sciences, Tehran, Iran Fereidoun Azizi Endocrine Research Center, Research Institute for Endocrine Sciences, Shahid Beheshti University of Medical Sciences, Tehran, Iran 2025 05 11 2025 09 30 Background: Several bioactive components are present in breast milk, which contribute to enhancing growth and development. Objectives: This study targeted to investigate the potential role of breast milk iodine concentration (BMIC), insulin-like growth factor-1 (IGF-I), and brain-derived neurotrophic factor (BDNF) during the early stage of lactation in child neurocognitive development. Methods: In this secondary analysis, we examined 122 breastfeeding mothers and their healthy children, all of whom were breastfed for at least six months. Levels of BDNF, IGF-1, and BMIC were assessed in breast milk samples obtained between the third and fifth days after lactation began. Three-year-old children were administered the Bayley-III screening test to assess their cognitive, motor, and language development. Results: The median (interquartile range) concentrations of iodine, BDNF, and IGF-1 in breast milk during the starting few days of lactation were 285.0 (181.0-366.0) µg/l, 0.59 (0.52-0.76) ng/ml, and 12.5 (9.6-18.3) ng/ml, respectively. The mean (standard deviation) cognitive, motor, and language scores were 101.0 (10.8), 93.4 (14.6), 100.1 (13.5) and, respectively. Linear regression models revealed a negative relation between breast milk iodine and children’s cognitive development ((β unadjusted = -0.004 (P = 0.010); β adjusted = -0.003 (P = 0.024)). However, no associations were found between breast milk BDNF and IGF-1 and cognitive, language, or motor scores in three-year-olds. Conclusion: Our findings indicated that early exposure to these breast milk components has no substantial association with neurodevelopment in three-year-old children. Further research is needed on breast milk components’ impact on child health. https://jfrh.tums.ac.ir/index.php/jfrh/article/view/3250 https://jfrh.tums.ac.ir/index.php/jfrh/article/download/3250/736