Iodine in commercial edible iodized salts and assessment of iodine exposure in Sri Lanka

Background: Iodine is an essential micronutrient used by the thyroid gland in the production of thyroid hormones. Both excessive and insufficient iodine intakes can cause thyroid diseases thus harmful to the human body. Inadequate iodine intake by human body causes Iodine Deficiency Disorders (IDD) and hypothyroidism. Excessive iodine intake causes Iodine Induced Hyperthyroidism (IIH). Universal Salt Iodization (USI) is the most effective way of preventing IDD. This study determined the concentrations of iodine species in commercial edible salt products, the stability of iodine at different conditions and iodine exposure at the consumer level. Methods: The iodine contents of six commercial edible iodized salts were determined qualitatively and quantitatively for both iodide and iodate. Thereafter, the first three products of highest iodine contents, the stability of iodide at exposed to air and heat was measured after 24 hours. Risk assessment of exposure was done at four levels considering the WHO estimation. Results: Results revealed that all of the salt products have excess iodine that is above the fortification level of 15-30mg kg^-1 level in Sri Lanka. Iodide stability was reduced at the average percentages of 13.1, 10.7 and 11.3. The iodate loss percentages were 0, 5.7 and 0 at open air. The iodide loss percentages at the temperature of 50 °C were 4.6, 7.8 and 8.6 while at 100 °C, loss percentages were 11.1, 11.4 and 15.9 for the same salt products. The iodine exposure at lower consumption during cooking ranged 244.4-432.2 μg/day while 325.9-576.3 μg/day for medium consumption, 407.4-720.4 μg/day for moderate high salt consumptions and 488.8-864.4 μg/day for high salt consumptions. As a total 95.8 % cases can cause IIH and only 4.1 % of them can provide optimal iodine nutrition in a population. Iodine exposure without cooking ranged 305.5-540.3 μg/day for low salt consumption, 407.4-720.4 μg/day for medium consumption and 509.2-900.5 μg/day for moderate high consumption and 611.1-1080.6 μg/day for high salt consumptions. Conclusions: All of the incidents (100 %) of consumption without cooking at the household level can cause excessive iodine intake and IIH in a population.