Subclinical Hypothyroidism and Elevated Thyroglobulin in Infants with Chronic Excess Iodine Intake

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