Stability of Iodine in Iodized Salt Used for Correction of Iodine-Deficiency Disorders. II

Abstract

The purpose of this study was to assess the effect of humidity and packaging materials on the stability of iodine in typical salt samples from countries with tropical and subtropical climates, under controlled climatic conditions. Initially we examined eight samples. In the second phase we expanded the study to salts from 18 sources and attempted to correlate the observed stability with salt impurities naturally present in these samples. High humidity resulted in rapid loss of iodine from salt iodized with potassium iodate, ranging from 30% to 98% of the original iodine content. Solid low-density polyethylene packaging protected the iodine to a great extent. High losses were observed from woven high-density polyethylene bags, which are often the packaging material of choice in tropical countries. Impurities that provided moisture at the salt surface had the most deleterious effect. Although clear correlations were not obtained, the presence of reducing agents, hygroscopic compounds of magnesium, and so forth seemed to have the most adverse effects on the stability of iodine. Surprisingly, carbonates had little effect on stability over the range present in the samples. Packaging salt in low-density polyethylene bags, which provided a good moisture barrier, significantly reduced iodine losses, and in most cases the iodine content remained relatively stable for six months to a year. The findings from this study indicate that iodine can be highly unstable, and in order to ensure the effectiveness of local salt-iodization programmes, countries should determine iodine losses from local iodized salt under local conditions of production, climate, packaging, and storage.

Seasonality in urinary and household salt iodine content among pregnant and lactating women of the plains of Nepal

“…Relative humidity, the type of packaging in which iodized salt is stored, and chemical impurities have a large impact on the retention of iodine in salt. Under experimental conditions, half the iodine content of salt was lost in 3 months when salt was stored in open containers at 100% relative humidity (Diosady et al, 1997). This demonstrated volatility of even potassium iodate, the more stable of the SI fortificants, likely explains the low proportion of iodized salt, and subsequent low concentrations of UI, during and following the monsoon season.…”

“…Household SI content has also been proposed as a proxy measure for assessing the adequacy of dietary iodine and, thus, population iodine status, with values of 20-50 ppm serving as a target range for adequacy (WHO/UNICEF/ICCIDD, 1994;Mannar & Dunn, 1995). Higher values in this range are more desirable where salt intakes may be low and conditions of high temperature and humidity, which accelerate iodine losses, are present (Diosady et al, 1997).…”

Iodine content in the marketed products of iodized salt: a descriptive study in southern Sri Lanka

“…Storage beyond 2 months aggravates loss of iodine from the salt due to different environmental conditions during storage and distribution (19). This might be due to the effect of physical or environmental factors like moisture content of the salt, humidity of the atmosphere, light, heat, and weather conditions.…”

Measurement of Iodine Availability and Stability of Some Iodized Salts in Bangladesh

“…It is proved that table salt is, consumed in relatively constant amounts (about 10 g/day), the great carrier of iodine, so it proved to be the most reliable way to take in iodine [11]. World Health Organization (WHO) and ICCIDD recommend that the amount of added iodine should be 20-40 mg/kg of salt [12]. In Bangladesh, the optimum level of fortification is 45-50 ppm at the production level, 20 ppm at the retail shop level and a minimum of 15 ppm at the consumption level [13].…”