Selenium intake and status of postpartum women and postnatal depression during the first year after childbirth in New Zealand - Mother and Infant Nutrition Investigation (MINI) study

Background: Selenium (Se) plays an important role in selenoproteins as an antioxidant, and is involved in thyroid function, mental health and child development. Selenium is low in the local food supplies in NZ. Low selenium intake has been reported in women of childbearing age and postmenopausal women, however, there is little research relating to breastfeeding women and their infants. Purpose: The study investigates maternal and infant selenium intake and status during the first year postpartum, and possible relationships to postnatal depression and anxiety. Basic procedures: The Mother and Infant Nutrition Investigation (MINI) study is an observational longitudinal cohort study. In total 87 breastfeeding mother-infant pairs were recruited and followed up at 3, 6 and 12 months postpartum. Maternal selenium intake was estimated from a four-day diet diary (4DDD). Selenium concentrations were measured in maternal spot urine, breastmilk and plasma; and infant spot urine samples. Postnatal depression was screened by the Edinburgh Postnatal Depression Scale (EPDS) questionnaire. Main findings: Median maternal selenium intake was 62 (50, 84) mu g/day, with 56 % below the Estimated Average Requirement (EAR) of 65 mu g/day. At 3, 6, and 12 months postpartum, median maternal urinary selenium:creatinine ratios were 29.0 (22.4, 42.0), 29.5 (23.1, 28.4), and 30.9 (24.3, 35.3) mu g/g; median infant urinary selenium concentrations (IUSC) were 8 (6,13), 11 (6, 15), and 24 (10, 40) mu g/L; median breastmilk selenium concentrations (BMSC) were 13 (11, 14), 11 (9, 11) and 12 (11, 13) mu g/L; 18 %, 11 % and 14 % of women reported probable minor depression based on the EPDS scores equal or above 10. Estimated median infant selenium intake at 3 and 6 months were 9 (8, 11) and 8 (7, 10) mu g/day with 85 % and 93 % below the Adequate Intake of 12 mu g/day. Median maternal plasma selenium was 105.8 mu g/L at 6 months postpartum. Minor depression at three months postpartum was significantly different across tertiles of plasma selenium concentrations (p = 0.041). Principle conclusions: Suboptimal selenium intake was observed among breastfeeding mothers and their infants in the MINI study. Potentially, some women had insufficient selenium status. Relation between selenium status and risk of postnatal depression and anxiety was inconclusive. Further research is required to explore effects on maternal thyroid function and infant neurodevelopment among women with inadequate selenium intake and status.