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

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Highlights

  • Inadequate dietary selenium intake was found in New Zealand postpartum women and their infants.

  • 23 % of postpartum women potential had inadequate selenium status.

  • 18 % of women had probable minor depression at three months postpartum.

  • 4 % of women remained depressed at twelve months postpartum.

Abstract

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) μg/day, with 56 % below the Estimated Average Requirement (EAR) of 65 μg/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) μg/g; median infant urinary selenium concentrations (IUSC) were 8 (6,13), 11 (6, 15), and 24 (10, 40) μg/L; median breastmilk selenium concentrations (BMSC) were 13 (11, 14), 11 (9, 11) and 12 (11, 13) μg/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) μg/day with 85 % and 93 % below the Adequate Intake of 12 μg/day. Median maternal plasma selenium was 105.8 μg/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.

Introduction

Selenium (Se) is essential in human health because selenoproteins play antioxidant and anti-inflammatory roles, and contribute to optimal levels of thyroid hormones [1]. Iodothyronine deiodinases are required for conversion of the inactive form of thyroid hormone (thyroxine, T4) to the active form (triiodothyronine, T3) [2]. Selenium as a component of the selenocysteine-containing proteins, glutathione peroxidase (GPx), protects the thyroid from oxidative damage [3]. Extremely low selenium intake has been associated with Keshan disease [4]. Selenium is thought to play a key role in optimal brain functioning [5]. Adequate dietary selenium intake has been found to improve mood among the general population, while low selenium intake is associated with low mood and an increased risk of de novo major depressive disorder in women [6,7]. This suggests that pregnant and postpartum women with low selenium intake may more at risk of experiencing postnatal depression, which affects 13 % of postpartum women globally [8].

In New Zealand, low levels of selenium in the food supply, and low selenium intakes have been reported in women of childbearing age [9] and postmenopausal women [10]. Low plasma selenium concentration among postpartum women and their infants resident in South Island of New Zealand (1998–1999) suggest inadequate status [11]. More recently, inadequate dietary selenium intake was reported in breastfeeding women three months after birth; however, selenium status from blood was not measured [12]. There are no current data describing selenium status among breastfeeding women in New Zealand. Given changes in dietary habits, food product availability and agricultural practices, continual monitoring of both selenium intake and status in this vulnerable postpartum population is essential. This study aims to investigate maternal and infant selenium intake and status during the first year postpartum. Furthermore, the relationship between selenium status and postnatal depression and anxiety will be investigated.

Section snippets

Study population

The Mother and Infant Nutrition Investigation (MINI) study is an observational longitudinal cohort study spanning the first year postpartum. Healthy breastfeeding women were recruited, in the Manawatu region, New Zealand, from June 2016 to December 2017. Women aged 16 years and older, who had given birth to a healthy term singleton infant aged less than three months were invited to join the study. Women were excluded: (1) if they developed significant health problems, such as metabolic disease

Results

In total, 87 breastfeeding women were recruited at three months postpartum, and most were followed up at six months (n = 78) and twelve months (n = 71). The mean age was 32 years, and 83 % were exclusively breastfeeding at three months after birth (Table 1). Most participants were Caucasian and achieved tertiary education. The majority had a vaginal delivery (78 %) and 44 % were delivering their first infant. In addition, 23 women reported that they had been smoking but most stopped for this

Sufficiency and deficiency

Suboptimal levels of dietary selenium intake were observed in our study participants. Maternal estimated selenium intake from the 4DDD was higher than previously reported from breastfeeding women (51 μg/day) from Palmerston North in 2009 and 2011 [12], and from Dunedin (South Island) between 2012 and 2013 [29]. The increase could be due to different dietary methods used in these studies. Weighed food records are suggested to be most precise dietary method in measuring usual nutrient intakes of

Conflict of interest

The authors declare no conflict of interest.

Funding

This work was supported by the Massey University Research Fund [no number, 2018], School of Food and Advanced Technology Postgraduate Fund [no number, 2016], and Oakley Mental Health Fund [no number, 2017]. The funding bodies played no role in the design of the study and collection, analysis, and interpretation of data or in the writing of the manuscript.

CRediT authorship contribution statement

Ying Jin: Conceptualization, Methodology, Investigation, Data curation, Formal analysis, Visualization, Writing - original draft, Writing - review & editing. Jane Coad: Conceptualization, Methodology, Funding acquisition, Supervision, Writing - review & editing. Rachael Pond: Resources, Writing - review & editing, Funding acquisition. Nick Kim: Resources, Writing - review & editing, Funding acquisition. Louise Brough: Conceptualization, Methodology, Funding acquisition, Formal analysis,

Acknowledgements

We thank the MINI team, including Ms. Anne Broomfield for her technical support and Ms. Rose Allen for her expertise in postnatal depression area. We would like to thank the women and their infants who volunteered for this study.

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