Selenium and iodine supplementation: effect on thyroid function of older New Zealanders.
What this study found
Selenium supplementation improved selenium status but did not improve thyroid hormone status, and iodine supplementation improved iodine status and lowered thyroglobulin but did not fully correct mild iodine deficiency over 12 weeks. Plasma selenium increased by week 12 in the selenium-containing groups, with unadjusted increases of 82% for selenium alone and 79% for selenium plus iodine; both were significant versus placebo after adjustment (P < 0.0001). Whole-blood GPx activity also increased with selenium alone by 4.5 U/g (95% CI: 2.7, 6.2) and with selenium plus iodine by 5.2 U/g (95%…
- Study & population
- Randomized, double-blind trial in noninstitutionalized older adults aged 60 to 80 years living in Dunedin, New Zealand.
- Intervention
- Participants received oral tablets once daily for 12 weeks: 100 μg selenium as L-selenomethionine, 80 μg iodine, or the combined 100 μg selenium plus 80 μg iodine regimen.
- Key limitation
- Each active arm was small (n = 25, 25, and 26), and the 12-week duration may have been too short to fully correct iodine deficiency or detect longer-term thyroid effects.
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Open PDFOriginal abstract
BACKGROUND The New Zealand population has both marginal selenium status and mild iodine deficiency. Adequate intakes of iodine and selenium are required for optimal thyroid function. OBJECTIVE The aim of the study was to determine whether low selenium and iodine status compromises thyroid function in an older New Zealand population. DESIGN We investigated the effects of selenium and iodine supplementation in a double-blind, randomized, placebo-controlled trial in 100 Dunedin volunteers aged 60-80 y. Participants received 100 microg Se/d as l-selenomethionine, 80 microg I, 100 microg Se + 80 microg I, or placebo for 3 mo. Thyroid-stimulating hormone (TSH), free triiodothyronine (T(3)), free thyroxine (T(4)), thyroglobulin, plasma selenium, whole-blood glutathione peroxidase (GPx) activity, and urinary iodine concentrations (UICs) were measured. RESULTS Plasma selenium (P < 0.0001) and whole-blood GPx activity (P<0.0001) increased from baseline to week 12 in the selenium and selenium plus iodine groups in comparison with the placebo group. Median UIC at baseline was 48 microg/L (interquartile range: 31-79 microg/L), which is indicative of moderate iodine deficiency. UIC increased in the iodine and selenium plus iodine groups and was significant only for the iodine group (P = 0.0014). Thyroglobulin concentration decreased by 24% and 13% of baseline in the iodine and selenium plus iodine groups in comparison with the placebo group (P = 0.009 and P = 0.108, respectively). No significant treatment effects were found for TSH, free T(3), free T(4), or ratio of T(3) to T(4). CONCLUSIONS Additional selenium improved GPx activity but not the thyroid hormone status of older New Zealanders. Iodine supplementation alleviated the moderate iodine deficiency and reduced elevated thyroglobulin concentrations. No synergistic action of selenium and iodine was observed. The trial was registered at www.anzctr.org.au/registry/ as ACTRN012605000368639.