Jessica Farebrother1, Michael B Zimmermann1,2, Vincent Assey2,3, Mary Christine Castro4, Mohamed Cherkaoui5, Ralph Fingerhut6, Qingzhen Jia7, Tomislav Jukic8,9, Anselimo Makokha10, Theofilo O San Luis2,11, Rita Wegmüller12, Maria Andersson1,2,13. 1. 1 Human Nutrition Laboratory, Institute of Food, Nutrition and Health, ETH Zurich, Switzerland. 2. 2 Iodine Global Network, Ottawa, Ottawa, Canada. 3. 3 Nutrition Services Section, Preventive Services Department; Ministry of Health, Community Development, Gender, Elderly, and Children, Dar es Salaam, Tanzania. 4. 4 Nutrition Center of the Philippines, Metro Manila, The Philippines. 5. 5 Faculté des Sciences Semlalia, Université Caddi Ayyed, Marrakech, Morocco. 6. 6 Swiss Newborn Screening Laboratory and Children's Research Center; University Children's Hospital Zurich, Zurich, Switzerland. 7. 7 Shanxi Institute for Prevention and Treatment of Endemic Disease, Linfen, P.R. China. 8. 8 Department of Nuclear Medicine and Oncology, Sestre Milosrdnice University Hospital Center and School of Medicine, University of Zagreb, Zagreb, Croatia. 9. 9 Faculty of Medicine Osijek, University Josip Juraj Strossmayer Osijek, Osijek, Croatia. 10. 10 Department of Food Science, Jomo Kenyatta University of Agriculture and Technology, Nairobi, Kenya. 11. 11 St Luke's Medical Center, Quezon City, Manila, The Philippines. 12. 12 Medical Research Council The Gambia, Keneba, The Gambia. 13. 13 Division of Gastroenterology and Nutrition; University Children's Hospital Zurich, Zurich, Switzerland.
Abstract
BACKGROUND: In areas with incomplete salt iodization coverage, infants and children aged 6-24 months weaning from breast milk and receiving complementary foods are at risk of iodine deficiency. However, few data exist on the risk of excessive iodine intake in this age group. Thyroglobulin (Tg) is a sensitive marker of iodine intake in school-age children and adults and may be used to estimate the optimal iodine intake range in infancy. The aim of this study was to assess the association of low and high iodine intakes with Tg and thyroid function in weaning infants. METHODS: This multicenter cross-sectional study recruited infants aged 6-24 months (n = 1543; Mage = 12.2 ± 4.6 months) receiving breast milk with complementary foods, from seven countries in areas with previously documented deficient, sufficient, or excessive iodine intake in schoolchildren or pregnant women. Urinary iodine concentration (UIC) and Tg, total thyroxine, and thyrotropin were measured using dried blood spot testing. RESULTS: Median UIC ranged from 48 μg/L (interquartile range 31-79 μg/L) to 552 μg/L (interquartile range 272-987 μg/L) across the study sites. Median Tg using dried blood spot testing was high (>50 μg/L) at estimated habitual iodine intakes <50 μg/day and >230 μg/day. Prevalence of overt thyroid disorders was low (<3%). Yet, subclinical hyperthyroidism was observed in the countries with the lowest iodine intake. CONCLUSIONS: Tg is a sensitive biomarker of iodine intake in 6- to 24-month-old infants and follows a U-shaped relationship with iodine intake, suggesting a relatively narrow optimal intake range. Infants with low iodine intake may be at increased risk of subclinical thyroid dysfunction. In population monitoring of iodine deficiency or excess, assessment of iodine status using UIC and Tg may be valuable in this young age group.
BACKGROUND: In areas with incomplete salt iodization coverage, infants and children aged 6-24 months weaning from breast milk and receiving complementary foods are at risk of iodine deficiency. However, few data exist on the risk of excessive iodine intake in this age group. Thyroglobulin (Tg) is a sensitive marker of iodine intake in school-age children and adults and may be used to estimate the optimal iodine intake range in infancy. The aim of this study was to assess the association of low and high iodine intakes with Tg and thyroid function in weaning infants. METHODS: This multicenter cross-sectional study recruited infants aged 6-24 months (n = 1543; Mage = 12.2 ± 4.6 months) receiving breast milk with complementary foods, from seven countries in areas with previously documented deficient, sufficient, or excessive iodine intake in schoolchildren or pregnant women. Urinary iodine concentration (UIC) and Tg, total thyroxine, and thyrotropin were measured using dried blood spot testing. RESULTS: Median UIC ranged from 48 μg/L (interquartile range 31-79 μg/L) to 552 μg/L (interquartile range 272-987 μg/L) across the study sites. Median Tg using dried blood spot testing was high (>50 μg/L) at estimated habitual iodine intakes <50 μg/day and >230 μg/day. Prevalence of overt thyroid disorders was low (<3%). Yet, subclinical hyperthyroidism was observed in the countries with the lowest iodine intake. CONCLUSIONS:Tg is a sensitive biomarker of iodine intake in 6- to 24-month-old infants and follows a U-shaped relationship with iodine intake, suggesting a relatively narrow optimal intake range. Infants with low iodine intake may be at increased risk of subclinical thyroid dysfunction. In population monitoring of iodine deficiency or excess, assessment of iodine status using UIC and Tg may be valuable in this young age group.