Determination of iodine level in consumer table salt from production to consumption: a cross-sectional study in occupied Palestinian territory

Abstract Background Iodination of table salt (salt for table use) is one of the best methods to eliminate iodine deficiency disorders (IDDs) and associated thyroid diseases. Iodate and iodide levels in table salt may vary for many reasons. There are no studies of the concentration of iodine in salt packs on the shelf and in use (open packs). This study aimed to quantify iodine in salt from twelve brands on the Palestinian market, either produced locally or imported, and both on the shelf and in use (opened). Methods Samples of table salt (99) were collected from randomly selected market places and households in eleven governorates of the occupied Palestinian territory. From each household, three samples were collected; the first when the consumer started to use the salt package, the second when the package was half consumed, and the third when the package was almost empty. In addition, 12 salt packages were purchased from a local market, one package for each studied brand. The samples were treated and the absorbance of iodate in the sample was measured using a spectrophotometer at 665·6 nm, based on a previous method. In brief, a specific mass of salt was dissolved, then potassium iodide, hydrochloric acid, methylene blue, and acetate buffer (pH 4) were added. The solution was mixed and diluted. A reference solution using 99% sodium chloride was also created with this method. Finally, the absorbance of iodate was measured, and the iodate concentration obtained by subtracting the absorbance of the sample solution from that of the reference solution. The iodate content was then compared to the content printed on the salt package. Iodine content was also quantified for a number of samples after exposure to oven heat or being boiled or heated in water, as well as after exposure to light or dark. Findings Of the 99 samples, 23 had lost 61% of their iodine content, 28 had lost 80%, and nine had lost all of their iodine. A little less than half (43 of 93) of the samples followed the Palestinian Standard regarding iodine content (3·5–5·5 mg per 100 g), and 70% (69 of 99) complied with the UNICEF recommendation (1·5 mg per 100 g). Iodine content in a newly opened pack (measured immediately after opening) was different from samples taken when the pack was half full, and when the pack was almost empty (0·023 mg/g, 0·0206 mg/g, and 0·0195 mg/g, respectively). The study also showed that up to 68% of iodine was lost during heating in a water solution, whereas dry heat led to a loss of 26%. Iodine loss was higher in light than in dark storage conditions (its concentration dropped from 48·2 mg/kg to 23·6 mg/kg in the dark, and decreased to 22·2 mg/kg in light). Interpretation A significant proportion of iodine is lost from salt after production and during consumption. There should be more awareness regarding the importance of using iodised salt, and education for consumers about salt storage. The iodine content in salt packages should be monitored by regulatory authorities. Funding None.