Study population
This is a cross-sectional descriptive study approved by the Human Ethics Committee of Thammasat University No. 1 (Faculty of Medicine). Infants aged 6 to12 months who attended the Well Baby Clinic at Thammasat University Hospital, from June 2016 to June 2017, were recruited randomly after informed consent was granted by their parents or legal guardians. Our inclusion criteria were term newborns (38-42 weeks gestation) with a birth weight between 2500-4000 grams having no prenatal and perinatal complications such as severe birth asphyxia, severe respiratory distress, or neonatal intensive care unit admission. Infants with chromosome abnormalities/syndromes, infectious/inflammatory diseases, and any acute health problems were excluded. All clinical samples from enrolled subjects were collected before routine universal iron supplementation. We collected demographic/clinical data through direct interviews with two investigators (PSi and PSu). Weight and length of participants were measured and evaluated by Z-score, according to WHO guidelines.26 The Z-scores of weight-for-lengths below or above two standard deviations (SD) are categorized as underweight and overweight, respectively.