Background – Suboptimal status of selenium and iodine has been reported in New Zealand adults. This is likely to be exacerbated in older adults who are particularly prone to inappropriate dietary intakes and inadequate nutrient status. Both selenium and iodine are essential for optimal thyroid hormone metabolism. To our knowledge, no studies have investigated the effect of a combined selenium and iodine intervention on thyroid status in both a low selenium and iodine region.
Objectives – To assess the efficacy of a selenium, iodine and combined selenium and iodine supplementation in older adults on thyroid hormone status, in comparison to a placebo.
Design – A randomized, double blind intervention trial was conducted in August and November 2005. Participants aged 60 to 80 years (n=102) consumed 100μg selenium as selenomethionine, 80μg iodine, 100μg selenium and 80μg iodine or placebo supplements daily for 12 weeks. Fasting, morning blood samples were taken at baseline, weeks 2, 4, 8 and 12 for measurement of thyroid hormone status (plasma TSH, free T3 and T4, and thyroglobulin) and selenium status (plasma selenium and whole blood glutathione peroxidase (GPx) activity). Median Urinary Iodine Concentration (MUIC) was determined at baseline and week 12 from casual urine samples.
Outcomes and Conclusions – Participants had a mean (SD) age of 73 (4.8) years and an average BMI of 27.4 (4.3). The MUIC was 48μg/L (IQR 31, 79), a level indicative of moderate iodine deficiency. Mean plasma selenium was 94.5 (25.7) μg/L and the correlation between plasma selenium and whole blood GPx was 0.329 (P=0.001). Selenium supplementation had no significant effect on plasma thyroid hormone concentrations. These results suggest the selenium intake of many of these older adults is still insufficient for optimal GPx activity, yet adequate for thyroid hormone status.