Jessica Farebrother1, Michael B Zimmermann1,2, Fatma Abdallah3, Vincent Assey4,5, Ralph Fingerhut6, Wanjiku N Gichohi-Wainaina7,8, Izzeldin Hussein9, Anselimo Makokha8, Kalil Sagno10, Juliawati Untoro11, Michael Watts12, Maria Andersson1,2,13. 1. 1 Human Nutrition Laboratory, Institute of Food, Nutrition, and Health , ETH Zurich, Zurich, Switzerland . 2. 2 Iodine Global Network , Ottawa, Canada . 3. 3 Tanzania Food and Nutrition Centre , Dar es Salaam, Tanzania . 4. 4 Nutrition Services Section, Preventive Services Department, Ministry of Health , Community Development, Gender, Elderly, and Children, Dar es Salaam, Tanzania . 5. 5 Regional Coordinator East and Southern Africa, Iodine Global Network , Ottawa, Canada . 6. 6 University Children's Hospital Zurich , Swiss Newborn Screening Laboratory and Children's Research Center, Zurich, Switzerland . 7. 7 International Crops Research Institute for Semi-Arid Tropics (ICRISAT) , Lilongwe, Malawi . 8. 8 Department of Food Science, Jomo Kenyatta University of Agriculture and Technology , Nairobi, Kenya . 9. 9 Regional Coordinator Middle East and North Africa, Iodine Global Network , Ottawa, Canada . 10. 10 Djibouti Country Office, United Nations Children's Fund , Djibouti, Djibouti . 11. 11 Eastern and Southern Africa Regional Office, United Nations Children's Fund , Nairobi, Kenya . 12. 12 Inorganic Geochemistry, Centre for Environmental Geochemistry, British Geological Survey , Nottingham, United Kingdom . 13. 13 Division of Gastroenterology and Nutrition, University Children's Hospital Zurich , Zurich, Switzerland .
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.
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 wateriodine 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: M Gao; W Chen; S Dong; Y Chen; Q Zhang; H Sun; Y Zhang; W Wu; Z Pan; S Gao; L Lin; J Shen; L Tan; G Wang; W Zhang Journal: Eur J Nutr Date: 2020-06-23 Impact factor: 5.614
Authors: Michael J Watts; Daniel R S Middleton; Andrew L Marriott; Olivier S Humphrey; Elliott M Hamilton; Amanda Gardner; Martin Smith; Valerie A McCormack; Diana Menya; Michael O Munishi; Blandina T Mmbaga; Odipo Osano Journal: Sci Rep Date: 2019-10-08 Impact factor: 4.379