Iodine status of pregnant women living in urban Johannesburg, South Africa.

Sicelosethu S Siro,Amy Wise,Lizelle Zandberg,Elizabeth A Symington,Jennifer Ngounda,Jeannine Baumgartner,Linda Malan,Cornelius M Smuts

doi:10.1111/mcn.13236

Abstract

Adequate intake of iodine is important during pregnancy because of its essential role in foetal growth and neurodevelopment. Data on iodine status of South African pregnant women are scarce, and the salt reduction policy implemented in 2016 may decrease iodine intake of South Africans. This cross‐sectional study assessed the iodine status of pregnant women residing in urban Johannesburg, South Africa. A total of 250 pregnant women were enrolled into the ‘Nutrition during Pregnancy and Early Development’ (NuPED) study and 312 pregnant women into the ‘Assessment of dried blood spot thyroglobulin in pregnant women to redefine the range of median urinary iodine concentration that indicates adequate iodine intake, South Africa’ (STRIPE‐SA) study and were included in this analysis. Urinary iodine concentration (UIC) was analysed in a spot urine sample. Thyroglobulin (Tg) was measured in serum, and thyroid‐stimulating hormone (TSH) and total thyroxine (tT4) were measured in dried blood spots. The median [interquartile range (IQR)] UIC of pregnant women was 144 (84–234) μg/L. Women in the first (n = 99), second (n = 262) and third (n = 174) trimester had a median UIC of 133 (81–316), 145 (84–236) and 156 (89–245) μg/L, respectively (p = 0.419). Median TSH, tT4 and Tg were 2.7 (2.3–3.2) mU/L, 202 (163–236) nmol/L and 9.2 (5.4–17.9) μg/L, respectively. Based on the median UIC, pregnant women residing in urban Johannesburg may be borderline iodine deficient. These findings highlight the need for ongoing monitoring of iodine status among vulnerable pregnant women, especially considering the recently introduced salt reduction policy in South Africa.

Highlights

Iodine is a vital element in the synthesis of thyroid hormones, which play a critical role in growth and brain development (Zimmermann, 2011)
A total of 250 pregnant women were enrolled into the ‘Nutrition during Pregnancy and Early Development’ (NuPED) study and 312 pregnant women into the ‘Assessment of dried blood spot thyroglobulin in pregnant women to redefine the range of median urinary iodine concentration that indicates adequate iodine intake, South Africa’ (STRIPE-SA) study and were included in this analysis
2.1 | Study design and participants. This cross-sectional study was performed in pregnant women who participated in two studies, namely the ‘Nutrition during Pregnancy and Early Development’ (NuPED) study (n = 250) and the ‘Assessment of dried blood spot thyroglobulin in pregnant women to redefine the range of median urinary iodine concentration that indicates adequate iodine intake, South Africa’ (STRIPE-SA) study (n = 312)

Summary

Introduction

Iodine is a vital element in the synthesis of thyroid hormones, which play a critical role in growth and brain development (Zimmermann, 2011). Though preventable, remains prevalent in all regions of the world (Zimmermann & Andersson, 2021). Iodine deficiency can lead to a range of adverse health outcomes depending on severity and occurrence in the human life cycle [Eastman & Zimmermann, 2018; World Health Organisation (WHO), 2013b]. The most serious consequences resulting from severe maternal iodine deficiency during pregnancy include stillbirth, foetal congenital anomalies and mental and growth restriction in offspring (Pearce et al, 2016). Pregnant women are susceptible to iodine deficiency because of increased demands to meet both increased maternal thyroid hormone production and foetal iodine needs and to compensate for increased renal iodine losses (Mioto et al, 2018; Pearce et al, 2016; Zimmermann, 2011). The World Health Organisation (WHO) recommends that pregnant women consume 250 μg of iodine per day, which is 100 μg more than recommended for non-pregnant and non-lactating women (WHO et al, 2007)

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