Iodine Supplementation of Mildly Iodine-Deficient Adults Lowers Thyroglobulin: A Randomized Controlled Trial.
What this study found
Iodine supplementation improved iodine status and lowered thyroglobulin, supporting thyroglobulin as a useful biomarker of iodine status in adults. Compared with placebo, thyroglobulin was 12% lower at 8 weeks (P = .045), 20% lower at 16 weeks (P < .001), and 27% lower at 24 weeks (P < .001), with a significant time-by-treatment interaction (P < .05). In the iodine arm, median thyroglobulin fell from 19.5 µg/L at baseline to 13.0 µg/L at 24 weeks; the 24-week median was 13.0 µg/L vs 16.2 µg/L in placebo. No adverse events were reported, and TSH and FT4 remained within normal ranges.
- Study & population
- Randomized, double-blind, placebo-controlled trial in mildly iodine-deficient adults aged 18-40 years living in Dunedin, New Zealand.
- Intervention
- Adults in the active arm received 150 µg/day iodine as potassium iodate mixed with cellulose in oral tablets, taken daily for 24 weeks.
- Key limitation
- The trial was relatively small and only 24 weeks long, which limits assessment of longer-term clinical outcomes.
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Open PDFOriginal abstract
CONTEXT An inverse relationship between thyroglobulin (Tg) and urinary iodine concentration (UIC) has been found in children, potentially making Tg a viable blood marker of iodine status. The application of Tg in adults is unknown. OBJECTIVE The objective of the study was to determine the efficacy of Tg to assess iodine status in adults. DESIGN This was a randomized, double-blind, placebo-controlled, clinical trial. SETTING The study was conducted in Dunedin, New Zealand. PARTICIPANTS Mildly iodine deficient adults (n = 112) aged 18–40 years participated in the study. INTERVENTION Participants were supplemented with 150 μg of iodine as potassium iodate or placebo daily for 24 weeks. At baseline and 24 weeks, participants provided five casual urine samples for UIC determination; serum TSH and free T4 (FT4) was also measured. Tg was determined at baseline and 8, 16, and 24 weeks. MAIN OUTCOME MEASURES A change in Tg concentration between the iodine-supplemented and placebo groups at 24 weeks. RESULTS At baseline, the overall median UIC was 65 μg/L, confirming that participants were mildly iodine deficient (ie, median UIC between 50 and 99 μg/L). The overall median Tg was 16.6 μg/L; TSH and FT4 were within normal reference ranges. At 24 weeks, the median UIC of the placebo and supplemented groups was significantly different, 79 and 168 μg/L, respectively (P < .001). Tg in the iodine-supplemented group decreased by 12%, 20%, and 27% compared with the placebo group at 8 (P = .045), 16 (P < .001), and 24 weeks (P < .001); there were no significant changes in TSH and FT4. CONCLUSION Improved iodine status as assessed by UIC was associated with a concomitant decrease in Tg concentration, demonstrating that Tg is a useful biomarker of iodine status in a group of adults.