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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. 2018 09; 28(9):1198-1210.T

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.

Authors+Show Affiliations

1 Human Nutrition Laboratory, Institute of Food, Nutrition, and Health , ETH Zurich, Zurich, Switzerland .1 Human Nutrition Laboratory, Institute of Food, Nutrition, and Health , ETH Zurich, Zurich, Switzerland . 2 Iodine Global Network , Ottawa, Canada .3 Tanzania Food and Nutrition Centre , Dar es Salaam, Tanzania .4 Nutrition Services Section, Preventive Services Department, Ministry of Health , Community Development, Gender, Elderly, and Children, Dar es Salaam, Tanzania . 5 Regional Coordinator East and Southern Africa, Iodine Global Network , Ottawa, Canada .6 University Children's Hospital Zurich , Swiss Newborn Screening Laboratory and Children's Research Center, Zurich, Switzerland .7 International Crops Research Institute for Semi-Arid Tropics (ICRISAT) , Lilongwe, Malawi . 8 Department of Food Science, Jomo Kenyatta University of Agriculture and Technology , Nairobi, Kenya .9 Regional Coordinator Middle East and North Africa, Iodine Global Network , Ottawa, Canada .8 Department of Food Science, Jomo Kenyatta University of Agriculture and Technology , Nairobi, Kenya .10 Djibouti Country Office, United Nations Children's Fund , Djibouti, Djibouti .11 Eastern and Southern Africa Regional Office, United Nations Children's Fund , Nairobi, Kenya .12 Inorganic Geochemistry, Centre for Environmental Geochemistry, British Geological Survey , Nottingham, United Kingdom .1 Human Nutrition Laboratory, Institute of Food, Nutrition, and Health , ETH Zurich, Zurich, Switzerland . 2 Iodine Global Network , Ottawa, Canada . 13 Division of Gastroenterology and Nutrition, University Children's Hospital Zurich , Zurich, Switzerland .

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't
Research Support, U.S. Gov't, Non-P.H.S.

Language

eng

PubMed ID

30019625

Citation

Farebrother, Jessica, et al. "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 : Official Journal of the American Thyroid Association, vol. 28, no. 9, 2018, pp. 1198-1210.
Farebrother J, Zimmermann MB, Abdallah F, et al. 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. 2018;28(9):1198-1210.
Farebrother, J., Zimmermann, M. B., Abdallah, F., Assey, V., Fingerhut, R., Gichohi-Wainaina, W. N., Hussein, I., Makokha, A., Sagno, K., Untoro, J., Watts, M., & 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 : Official Journal of the American Thyroid Association, 28(9), 1198-1210. https://doi.org/10.1089/thy.2018.0234
Farebrother J, et al. 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. 2018;28(9):1198-1210. PubMed PMID: 30019625.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - 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. AU - Farebrother,Jessica, AU - Zimmermann,Michael B, AU - Abdallah,Fatma, AU - Assey,Vincent, AU - Fingerhut,Ralph, AU - Gichohi-Wainaina,Wanjiku N, AU - Hussein,Izzeldin, AU - Makokha,Anselimo, AU - Sagno,Kalil, AU - Untoro,Juliawati, AU - Watts,Michael, AU - Andersson,Maria, Y1 - 2018/08/22/ PY - 2018/7/19/pubmed PY - 2019/5/6/medline PY - 2018/7/19/entrez KW - groundwater KW - iodine excess KW - salt iodization KW - thyroglobulin KW - thyroid function KW - urinary iodine concentration SP - 1198 EP - 1210 JF - Thyroid : official journal of the American Thyroid Association JO - Thyroid VL - 28 IS - 9 N2 - 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. SN - 1557-9077 UR - https://www.unboundmedicine.com/medline/citation/30019625/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_ L2 - https://www.liebertpub.com/doi/full/10.1089/thy.2018.0234?url_ver=Z39.88-2003&rfr_id=ori:rid:crossref.org&rfr_dat=cr_pub=pubmed DB - PRIME DP - Unbound Medicine ER -