title: Subclinical Hypothyroidism and Elevated Thyroglobulin in Infants with Chronic Excess Iodine Intake.
abstract: BACKGROUND
  Acute iodine excess in newborns can cause hypothyroidism, but there are limited data on the effects of iodine excess on thyroid function in older infants. The aim of this study was to measure the effects of chronic excess iodine intake on thyroid function in 6-24-month-old infants.
  
  
  METHODS
  In this cross-sectional study, infants (n=696) in eastern Nepal were studied. Spot urine samples, venous blood samples, and household salt samples were collected, and urinary iodine concentration (UIC), serum free thyroxine (fT4), thyrotropin (TSH), thyroglobulin (Tg), and titrated household salt iodine concentration (SIC) were measured. Daily iodine intake was calculated from UIC based on estimates of urine volume at this age.
  
  
  RESULTS
  Median (25th-75th percentile) household SIC was 89 (70-149) ppm, while national legislation stipulates a fortification level of 50 ppm. Median UIC was 407 (312-491) μg/L; 76% of infants had a UIC >300 μg/L, suggesting iodine excess. Calculated mean iodine intake in 12-24-month-old infants was 220 μg/day, exceeding the recommended safe upper limit for iodine at this age (200 μg/day). Among the infants, 15.8% had an elevated Tg, 7.4% had subclinical hypothyroidism, but <1% had overt hypothyroidism. UIC was not a significant predictor of thyroid function, thyroid hormones, or Tg.
  
  
  CONCLUSIONS
  In 6-24-month-old infants exposed to excessive iodine intake, ∼7% have subclinical hypothyroidism but <1% have overt hypothyroidism. These findings suggest the thyroid in late infancy is already able to adapt to high iodine intakes and, in most cases, maintain euthyroidism.
authors.affiliation: 1 Department of Biochemistry, B.P. Koirala Institute of Health Sciences , Dharan, Nepal .
authors.forename: Ashwini Kumar
authors.initials: AK
authors.lastname: Nepal
authors.affiliation: 1 Department of Biochemistry, B.P. Koirala Institute of Health Sciences , Dharan, Nepal .
authors.forename: Ranjan
authors.initials: R
authors.lastname: Suwal
authors.affiliation: 1 Department of Biochemistry, B.P. Koirala Institute of Health Sciences , Dharan, Nepal .
authors.forename: Sharad
authors.initials: S
authors.lastname: Gautam
authors.affiliation: 2 Department of Pediatric and Adolescent Medicine, B.P. Koirala Institute of Health Sciences , Dharan, Nepal .
authors.forename: Gauri Shankar
authors.initials: GS
authors.lastname: Shah
authors.affiliation: 1 Department of Biochemistry, B.P. Koirala Institute of Health Sciences , Dharan, Nepal .
authors.forename: Nirmal
authors.initials: N
authors.lastname: Baral
authors.affiliation: 3 Human Nutrition Laboratory, Institute of Food Nutrition and Health, Swiss Federal Institute of Technology (ETH) , Zurich, Switzerland .
authors.forename: Maria
authors.initials: M
authors.lastname: Andersson
authors.affiliation: 3 Human Nutrition Laboratory, Institute of Food Nutrition and Health, Swiss Federal Institute of Technology (ETH) , Zurich, Switzerland .
authors.forename: Michael Bruce
authors.initials: MB
authors.lastname: Zimmermann
mesh_terms: D002675:Child, Preschool; D015331:Cohort Studies; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007037:Hypothyroidism / Q000097:blood / Q000139:chemically induced*; D007223:Infant; D007455:Iodine / Q000506:poisoning* / Q000652:urine; D008297:Male; D009390:Nepal; D017673:Sodium Chloride, Dietary / Q000506:poisoning*; D013954:Thyroglobulin / Q000097:blood; D013972:Thyrotropin / Q000097:blood; D013974:Thyroxine / Q000097:blood
chemical_list: D017673:Sodium Chloride, Dietary; C034024:iodized salt; D013972:Thyrotropin; D013954:Thyroglobulin; D007455:Iodine; D013974:Thyroxine