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Nutrients 2018, 10(6), 736; https://doi.org/10.3390/nu10060736

Iodine Status Assessment in South African Adults According to Spot Urinary Iodine Concentrations, Prediction Equations, and Measured 24-h Iodine Excretion

1
School of Medicine, University of Wollongong, Wollongong 2500, New South Wales, Australia
2
Illawarra Health and Medical Institute, University of Wollongong, Wollongong 2500, New South Wales, Australia
3
Hypertension in Africa Research Team (HART), North-West University, Potchefstroom 2531, North West Province, South Africa
4
MRC/Wits Developmental Pathways for Health Research Unit, University of the Witwatersrand, Johannesburg 2193, Gauteng, South Africa
5
Centre of Excellence for Nutrition (CEN), North-West University, Potchefstroom 2531, North West Province, South Africa
6
Statistical Consultation Services, North-West University, 11 Hoffman Street, Potchefstroom; Private Bag X6001, Potchefstroom 2520, North West Province, South Africa
7
MRC Research Unit for Hypertension and Cardiovascular Disease, North-West University, Potchefstroom 2531, North West Province, South Africa
8
World Health Organization (WHO), Avenue Appia 20, CH-1211 Geneva 27, Switzerland
9
Research Centre for Generational Health and Ageing, University of Newcastle, Newcastle 2308, New South Wales, Australia
*
Author to whom correspondence should be addressed.
Received: 12 May 2018 / Revised: 31 May 2018 / Accepted: 1 June 2018 / Published: 7 June 2018
(This article belongs to the Special Issue Iodine and Health throughout the Lifecourse)
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Abstract

The iodine status of populations is conventionally assessed using spot urinary samples to obtain a median urinary iodine concentration (UIC) value, which is assessed against standard reference cut-offs. The assumption that spot UIC reflects daily iodine intake may be flawed because of high day-to-day variability and variable urinary volume outputs. This study aimed to compare iodine status in a sample of South African adults when determined by different approaches using a spot urine sample (median UIC (MUIC), predicted 24 h urinary iodine excretion (PrUIE) using different prediction equations) against measured 24 h urinary iodine excretion (mUIE). Both 24 h and spot urine samples were collected in a subsample of participants (n = 457; median age 55 year; range 18–90 year) in the World Health Organization Study on global AGEing and adult health (SAGE) Wave 2 in South Africa, in 2015. Kawasaki, Tanaka, and Mage equations were applied to assess PrUIE from predicted urinary creatinine (PrCr) and spot UIC values. Adequacy of iodine intake was assessed by comparing PrUIE and mUIE to the Estimated Average Requirement of 95 µg/day, while the MUIC cut-off was <100 µg/L. Bland Altman plots assessed the level of agreement between measured and predicted UIE. Median UIC (130 µg/L) indicated iodine sufficiency. The prediction equations had unacceptable bias for PrUIE compared to measured UIE. In a sample of adult South Africans, the use of spot UIC, presented as a group median value (MUIC) provided similar estimates of inadequate iodine status, overall, when compared to EAR assessed using measured 24 h iodine excretion (mUIE). Continued use of MUIC as a biomarker to assess the adequacy of population iodine intake appears warranted. View Full-Text
Keywords: iodine; median urinary concentration; 24 h urine collection; prediction equations; agreement; estimated average requirement iodine; median urinary concentration; 24 h urine collection; prediction equations; agreement; estimated average requirement
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).
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Charlton, K.E.; Ware, L.J.; Baumgartner, J.; Cockeran, M.; Schutte, A.E.; Naidoo, N.; Kowal, P. Iodine Status Assessment in South African Adults According to Spot Urinary Iodine Concentrations, Prediction Equations, and Measured 24-h Iodine Excretion. Nutrients 2018, 10, 736.

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