Effect of Excess Iodine Intake from Iodized Salt and/or Groundwater Iodine on Thyroid Function in Nonpregnant and Pregnant Women, Infants, and Children: A Multicenter Study in East Africa

Farebrother, J and Zimmermann, M B and Abdallah, F and Assey, V and Fingerhut, R and Gichohi-Wainaina, W N and Hussein, I and Makokha, A and Sagno, K and Untoro, J and Watts, M and Andersson, M (2018) Effect of Excess Iodine Intake from Iodized Salt and/or Groundwater Iodine on Thyroid Function in Nonpregnant and Pregnant Women, Infants, and Children: A Multicenter Study in East Africa. Thyroid (TSI), 28 (9). pp. 1198-1210. ISSN 1050-7256

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Abstract

Background: Acute excess iodine intake can damage the thyroid, but the effects of chronic excess iodine intake are uncertain. Few data exist for pregnant and lactating women and infants exposed to excessive iodine intake. Methods: This was a multicenter cross-sectional study. At study sites in rural Kenya and urban Tanzania previously reporting iodine excess in children, urinary iodine concentration (UIC), thyrotropin, total thyroxine, and thyroglobulin (Tg) were measured in school-age children (SAC), women of reproductive age, pregnant (PW) and lactating women, and breast-feeding and weaning infants. In a national study in Djibouti, UIC was measured in SAC and PW. At all sites, daily iodine intake was estimated based on UIC, and iodine concentration was measured in household salt and drinking water. Results: The total sample size was 4636: 1390, 2048, and 1198 subjects from Kenya, Tanzania, and Djibouti, respectively. In Kenya and Tanzania: (i) median UIC was well above thresholds for adequate iodine nutrition in all groups and exceeded the threshold for excess iodine intake in SAC; (ii) iodine concentrations >40 mg of iodine/kg were found in approximately 55% of household salt samples; (iii) iodine concentrations ≥10 μg/L were detected in 9% of drinking water samples; (iv) Tg was elevated in all population groups, but the prevalence of thyroid disorders was negligible, except that 5–12% of women of reproductive age had subclinical hyperthyroidism and 10–15% of PW were hypothyroxinemic. In Djibouti: (i) the median UIC was 335 μg/L (interquartile range [IQR] = 216–493 μg/L) in SAC and 265 μg/L (IQR = 168–449 μg/L) in PW; (ii) only 1.6% of Djibouti salt samples (n = 1200) were adequately iodized (>15 mg/kg); (iii) the median iodine concentration in drinking water was 92 μg/L (IQR = 37–158 μg/L; n = 77). In all countries, UIC was not significantly correlated with salt or water iodine concentrations. Conclusions: Although iodine intake was excessive and Tg concentrations were elevated, there was little impact on thyroid function. Chronic excess iodine intake thus appears to be well tolerated by women, infants, and children. However, such high iodine intake is unnecessary and should be avoided. Careful evaluation of contributions from both iodized salt and groundwater iodine is recommended before any review of iodization policy is considered.

Item Type: Article
Divisions: Research Program : East & Southern Africa
CRP: UNSPECIFIED
Uncontrolled Keywords: East Africa, iodine excess, urinary iodine concentration, thyroid function, thyroglobulin, salt iodization, groundwater
Subjects: Others > Water Resources
Others > Gender Research
Others > East Africa
Depositing User: Mr Ramesh K
Date Deposited: 15 Oct 2018 08:58
Last Modified: 06 Dec 2018 03:42
URI: http://oar.icrisat.org/id/eprint/10892
Official URL: http://dx.doi.org/10.1089/thy.2018.0234
Projects: UNSPECIFIED
Funders: USAID Grant through the United Nations Children’s Fund to support the Sustainable Elimination of Iodine Deficiency, and the ETH Zurich (Switzerland). Additional funding support for the study in Djibouti was provided by the Iodine Global Network (Ottawa, C
Acknowledgement: We would like to sincerely thank the following persons for their implication in this study: Francesca Chepkirui, Sofia De Rosso, Annemarie Geutjes, Gerrad Jones, Alida Melse Boonstra, Vera Hu¨rlimann, Juma Peter Kaswahili, Michael Maganga, Katja Schoenenberger, Manasi Shrouti, Sara Stinca, Kevin Szillat, Elise Talsma, Stephanie Teixeira, Lenny Winkel, all staff at Kibwezi Health Centre laboratory, all staff at Tanzania Food and Nutrition Centre and the Nutrition Services Section of the Ministry of Health, Tanzania, the Municipal Council of Kinondoni, Dar Es Salaam, Tanzania, and staff at the Nutrition and Dietetics Unit of the Ministry of Health, Kenya. Funding for this study was provided by a USAID Grant through the United Nations Children’s Fund to support the Sustainable Elimination of Iodine Deficiency, and the ETH Zurich (Switzerland). Additional funding support for the study in Djibouti was provided by the Iodine Global Network (Ottawa, Canada) and United Nations Children’s Fund Djibouti country office. At the time of writing, J.U. was a staff member of the United Nation Children’s Fund (UNICEF). The author alone is responsible for the views expressed in this publication, which do not necessarily represent the decisions, policy, or views of UNICEF.
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