Abstract
Iodine and selenium are required for thyroid function. This study investigated iodine and selenium intakes in healthy, women aged 50–70 years (n = 97) from three cities in the North Island of New Zealand, after mandatory fortification of bread with iodised salt. Iodine and selenium concentrations were determined in 24-h urine samples; daily intakes were extrapolated from amounts in urine (90% and 55% of daily intake, respectively). Three day diet diaries (3DDD) also estimated selenium and iodine (excluding iodised salt) intake. Median urinary iodine concentration (UIC) was 57 (41, 78) µg/L, indicating mild iodine deficiency. Estimated median iodine intake based on urine was 138 (100, 172) µg/day, below Recommended Dietary Intake (RDI) (150 µg/day) with 25% below Estimated Average Requirement (EAR) (100 µg/day). Estimated median selenium intake was 50 (36, 71) µg/day based on urine and 45 (36, 68) µg/day using 3DDD, below RDI (60 µg/day) with 49%–55% below EAR (50 µg/day). Median bread intakes were low at 1.8 (1.1, 2.7) serves/day; 25% consumed ≤1 serve/day. Although population iodine intakes improved following mandatory fortification, some had low intakes. Selenium intakes remain low. Further research should investigate thyroid function of low consumers of iodine fortified bread and/or selenium in New Zealand.
Highlights
The New Zealand food supply contains low levels of iodine and selenium [1]
A complete data set of iodine, selenium and creatinine excretion and dietary data were available for 97 participants, the data analysis presented here is based on these 97 samples only
A limitation of the current study is not measuring selenium or glutathione peroxidase (GPx) activity in blood, determining daily urinary selenium excretion serves as a proxy measure for selenium intake, and the current study indicates the need for further research in this population
Summary
The New Zealand food supply contains low levels of iodine and selenium [1]. Both nutrients are required for thyroid function and the thyroid gland contains the highest concentration of these minerals in the human body [2]. Iodine is a constituent of the thyroid hormones, thyroxine (T4) and triiodothyronine (T3), whereas selenium-dependent iodinase generates the active T3 form from the inactive T4 form [2]. Selenium is a constituent of the antioxidant enzyme glutathione peroxidase (GPx); iodine deficiency can result in accumulation of hydrogen peroxide and concurrent selenium deficiency may impair the degradation of hydrogen peroxide leading to damage of the thyroid gland [2]. Selenium deficiency could potentially exacerbate the consequences of mild iodine deficiency which is present in New Zealand [4]
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