Iodine is an essential trace element for human health [1]. Iodine is used by the thyroid gland in the production of thyroxin (T4) and triiodothyronine (T3) hormones that regulate the metabolism of physiological processes of the human body [1]. However, both excessive and insufficient iodine intakes can cause thyroid diseases thus harmful to the human body [2].
Inadequate iodine intake by human body causes the insufficient synthesis of thyroid hormones, resulting hypothyroidism and Iodine Deficiency Disorders (IDD) [3]. Hypothyroidism is a condition of which the thyroid hormone level in the blood lowers [4] since thyroid glands do not produce enough thyroid hormones [3]. IDD contains a collection of functional and developmental abnormalities such as endemic goiter, abortions, still births, cretinism, retarded physical development, brain damage and irreversible mental retardation [1–3]. Excessive iodine intake from food and water can also have adverse chronic health effect such as Iodine Induced Hyperthyroidism (IIH), thyroiditis, goiter, thyroid papillary cancer and thyrotoxicosis” [5–8]. Long term excessive iodine intake increases the activity of Thyroid Stimulating Hormone (TSH) and reduces thyroid hormone production, through loss of the “escape” phenomenon after the Wolff-Chaikoff effect (inhibits organification in the thyroid gland, the formation of thyroid hormones inside the thyroid follicle, and the release of thyroid hormones into the bloodstream) resulting in low thyroid hormone levels, or hypothyroidism in fetuses and newborns [9]. Chronic exposure of iodine in several milligrams per day (1100 ?g/day) can disrupt thyroid function [10]. Correspondingly, a clear relationship between excessive iodine intake and distribution of differentiated thyroid cancer and the risk of IIH after correction of iodine deficiency have been identified [5, 6, 9].
Universal Salt Iodization (USI) is the most effective way of preventing IDD [4]. Salt is an excellent carrier for iodine, as it is consumed at relatively constant, well-defined levels by all individuals within a society, independently of economic status [11]. According to the WHO, the recommended iodine intake for the adults should be 150 ?g per day and recommended iodine intake for pregnant women is 200 to 250 ?g per day [12]. Hence to provide 150 ?g daily requirement of iodine for each person, the salt iodine concentration at the point of production should be 20–40 mg per 1 kg of iodized salt [12]. That recommended level was estimated by WHO, under the assumptions of 20 % loss of iodine from production site to household, 20 % loss when cooking and 10 g of salt as average salt intake per capita [12]. It is understood that the actual availability of iodine in salt depends on its form of fortification, environmental and other factors. On exposure to sunlight, wind, salts iodized as iodide lose a considerable amount of iodine while the salts iodized with iodate has shown no losses. Even when heating, the salts containing potassium iodate retained a high percentage of their original iodine content while the salts iodized with potassium iodide had lost a considerable amount of iodine [13, 14]. The recommended iodine intake is also known as Recommended Dietary Allowances (RDA) that means the average daily level of iodine intake sufficient to meet the nutrient requirements of nearly 97.5 % healthy individuals [15]. According to the WHO, the upper tolerance limit of iodine for adults is 1100 ?g/day [2].
The iodination program in Sri Lanka was formally implemented in 1995 to avoid IDD in the population [16]. High prevalence of IDD (30-45 %) has been reported over 20 years from 1995 with an estimation of affecting population as 10 million (Fernando et al., 1989; Fordyce et a., 2003). The causes of IDD prevalency is suggested to be multifactorial, due to the existence of humic substance, clay minerals etc. that exert an influence of the bioavailability of iodine (Dissanayake and Chandrajith, 1996). Hence, drastic reduction of IDD was expected by implementing salt iodination however, still goiter is prominently seen as pockets which could be due to selenium deficiency (Fernando et al., 2015; Fordyce et al., 2000). However at present, it has been reported that there are high prevalence of IIH and slightly high concentrations of iodine in urine especially in female adolescents (213.1 ?g/L) in Sri Lanka, which may be due to excessive iodine intake from salt due to lack or regulations and monitoring [17–19]. The iodine fortification level in Sri Lanka is 15–30 mg/kg for a salt packet, according to the Food Regulations (2005). Only a few studies have been conducted on assessing iodine in commercial salt products in Sri Lanka and data are quite old [20]. The authors reported that the iodine content in 68.6 % of the packets was outside the range stipulated by the Sri Lanka Standards Institution (SLSI). In 52.8 %, the mean iodine content was above the recommended upper limit of 40 mg/kg and in 15.8 % below the recommended lower limit of 20 mg/kg. Non-iodised salt is not available in Sri Lankan market today at the same time many salt products coming up to the market and most probably with excessive iodine concentrations. Many comprehensive studies around the world have reported an increase in the IIH followed by the iodisation [21, 22].
Therefore, it is vital to determine their iodine concentrations to check whether they follow the recommended fortification level at the point of production. Since the iodine status is analogous to the iodine exposure, it can be used directly for the risk assessment of iodine exposure which may indirectly provide a prediction about the health condition of the population [23, 24]. Hence, experiments were conducted to assess iodine in commercial edible iodized salts to determine the concentrations of iodine species in commercial edible salt products available in the local market, examine the actual availability of iodine varies with its exposure to air and at different cooking practices and to assess the iodine exposure at consumer level to estimate risks.