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Salt iodine variation within an extended Guatemalan community: The failure of intuitive assumptions
Christopher Stewart, Noel Solomons, and Ivan Mendoza with the collaboration of Sandy May and Glen Maberly
During the 13 years after iodized salt was introduced into Guatemala in 1952, the prevalence of goitre fell from 39% to 5%, and for many years thereafter it was difficult to find examples of endemic goitre to demonstrate to students on field visits. However, with the political turmoil of the 1980s, the iodization of salt in Guatemala lapsed and goitre returned. An effort is being made to restore an effective iodization programme. The results are still highly unsatisfactory, as the following article reports. If the problem were specific to Guatemala, this article would not have been accepted for publication. Unfortunately, it serves as a reminder of a situation that prevails in many developing countries today even when their salt or part of it is stated to be iodized. Government regulatory authorities and United Nations institutions should be alerted by this article to carry out similar evaluations in their own countries on a continuing basis.
Guatemalan law mandates an iodine concentration from 30 to 700 parts per million (ppm) in all table salt offered in local commerce. Forty-four specimens of salt were collected in urban and rural sectors of a county on the outskirts of the capital of Guatemala and analysed for their iodine content by an iodate titration method. The concentrations ranged from 1 to 117 ppm, (mean ± SD 26.6 ± 21.7 ppm, median 24 ppm). Salt samples with iodine in both the adequate and the inadequate ranges were found in each of five subjurisdictions (township and four hamlets), and the median concentration was equivalent at all sites, without an urban-to-rural gradient. Similarly, the mandated iodine concentration was no more likely to be found in salt packaged under a brand name with a commercial label than in salt in a plain, unlabelled package. The findings place in relief the continuing difficulties in Guatemala in the effort to provide a universally protective level of iodine in table salt.
Several recent international meetings and agreements have focused on the worldwide problem of micronutrient malnutrition [1 4], and efforts have commenced to redress the issue. Iodine is one of the three micronutrients that have been singled out, together with vitamin A and iron, for priority attention . iodine-deficiency disorders can result in endemic goitre, cretinism, and excess mortality [5, 6], and deficient iodine status is also an impediment to adequate scholastic performance [7, 8].
Universal iron fortification of table salt has been heralded as the sure and sustainable solution to the endemicity of iodine-deficiency disorders , and a major international effort to implement the process has begun. Guatemala has had a law mandating the fortification of salt with iodine (iodate) on its books since 1954; the limits have been set at 30 to 100 ppm since 1993. In 1987, analysis of 50 specimens of salt from across the country found that 86% had a concentration below 60 ppm, the legal criterion at that time . In 1994, analysis of 44 samples from various metropolitan and countryside locations found that 97% had an iodine concentration inferior to 60 ppm and 64% fell within the currently mandated range .
After the wide variation in salt iodine content on a national level had been thus established  and confirmed , we considered it important to focus an inquiry on a restricted region. In preparation for a comparison of iodine status indicators, the present survey of salts was performed in the target township and surrounding rural hamlets near the capital.
Materials and methods
A total of 44 samples were collected from five defined geographic areas in the county of San Pedro Sacatepequez in the province of Guatemala. The township of the same name is reached by an asphalt highway of two to four lanes and is 20 km from the centre of the capital, Guatemala City. It has an estimated population of 19,550. The four hamlets included in the sampling were El Pilar, Buena Vista, Vista Hermosa, and Pajoc. Their respective estimated populations were 4,600, 1,500, 5,000, and 2,600, and their distances from the township 10, 2, 3, and 7 km. This has traditionally been an area of subsistence and commercial agriculture, but it has experienced a recent influx of light industry. The population is 90% indigenous, belonging to the post-Mayan Kakchiquel linguistic group The number of samples collected ranged from 4 in the two smallest hamlets to 21 in the urban township.
The samples were collected during the dry season between February and April 1995. They were purchased from vendors in either marketplaces or small neighbourhood shops chosen at random within each locality. The notations included the site of purchase and whether or not the package had an identifying label. The samples were given specimen numbers and packed in plastic bags pending transport to Atlanta, Georgia, USA.
The technique used in Atlanta to analyse quantitatively the iodate content of salt samples is iodometric titration . Free iodine is liberated from the sample and titrated with thiosulphate, using starch as an external indicator. This technique is specific for iodate and will not detect the presence of iodide. The coefficient of variation of the measurements was less than 15%. The iodine concentration is expressed in iodate equivalents as parts per million (ppm).
Data and statistical analysis
The arithmetic means, standard deviations, and medians of the iodine concentrations were calculated for the total of the samples and for subgroups, disaggregated by packaging and geography. Differences among subgroups were tested for statistical significance with the x2 test for categorical classifications and Student's t test, with iodine concentration as a continuous variable. A probability below 5% was considered significant.
Figure 1 (see FIG. 1. Percentage frequency of salt iodine concentration for the 44 samples collected in the county of San Pedro Sacatepequez) is a histogram of the distribution of iodine content in the 44 samples. The concentrations varied from 1 to 117 ppm, with a global median of 24 ppm. Twenty-seven of the samples (61%) had a content below 30 ppm, the lower limit of the legislative mandate.
Table 1 shows the geographic distribution of iodine content in the salt samples. Both adequate and inadequate iodate levels in salt were found in each of the sites. The percentage of samples with adequate (230 ppm) salts ranged from 25% in Pajoc to 75% in Vista Hermosa. Taken as a group, of the 23 samples from the four hamlets, 9 (39%) had adequate iodine contents and 14 (61%) had inadequate iodine contents. Of the 21 samples collected within the confines of the township, 8 (38%) had adequate iodine and 13 (62%) had inadequate iodine (p < .05). The mean iodine content was 28.1 ± 26.6 ppm (median 24 ppm) in the urban area and 24.8 ± 15.0 ppm (median 24 ppm) in the hamlets (p < .05).
TABLE 1. Distribution of concentration of iodine in salt samples from the five geographic sites
|San Pedro Sacatepequez||urban||21||24||1||117|
Twenty (45%) of the samples were sold in plain plastic bags and 24 (55%) in bags labelled "iodized salt." Figure 2 (see FIG. 2. Frequency of samples with inadequate (left), adequate (middle), and excess (right) concentrations of salt iodine. The shaded area of each bar represents the specimens purchased in labelled, brand-name packets) shows the number of samples with adequate and inadequate iodine contents according to whether or not they were labelled as iodized salt. Fifty-nine percent of the samples with adequate iodine and 52% of those with inadequate iodine came in packages with an identifying brand name and label indicating "iodized salt" (p > .05). Stated another way, 58% of brand-name specimens and 65% of unlabelled specimens had iodine concentrations below the lower limit prescribed by law.
The standard for countries with well-regulated and well-standardized commercial production of iodized salt is generally to have relatively homogeneous stocks, all with iodine content in accordance with their package label and within the specified and advertised limits. This would apply to industrialized nations such as the United States and Canada. Alternatively, without an attempt at iodine fortification, mined salt and even sea salt will have background iodine contents of 0 to 10 ppm. Variation in iodine content is a relatively recent phenomenon, uncovered with the advent of attempts to implement iodization of salt in developing countries with traditionally elevated prevalences of iodine-deficiency disorders. Uneven salt iodine concentrations were uncovered in surveys in the northern Indian Uttar Pradesh region , among 40 of the 44 districts in Kenya , and across the country of Guatemala .
A survey of 36 salt samples from different parts of Guatemala found a median iodine content of 7 ppm and a range of 0 to 64 ppm . There was a definite tendency towards more iodine in samples collected from cities and larger towns than in those from smaller and more rural sites, consistent with the trend reported around the world. Six packages of iodized salt of the same commercial brand from a supermarket chain in Guatemala City advertised concentrations within the range of 30 to 100 ppm . Hence, we hypothesized that salt purchased in the more urban setting (township) would have higher iodine content than that bought in rural hamlets, and that salt with a commercial identification on the package would be more likely to be iodized than salt of a no-name brand. However, our results do not support these hypotheses: we found no urban-rural difference in the municipality of San Pedro Sacatepequez and no difference in iodine content between samples labelled as iodized and those not so labelled.
As in our earlier study , the iodine contents in more than 60% of salt samples were below the mandated range; compared with the national sample, however, the median concentration in this specific district was three times higher (24 vs 7 ppm) but still below the minimum mandated level of 30 ppm. We can only speculate on the reasons for the less than adequate iodine levels in a majority of the salt samples from San Pedro Sacatepequez county and from throughout the country .
A number of factors are known to influence the stability of iodine in salt, such as the duration of storage, size of salt crystals, impurities, moisture of the salt, ambient temperature and humidity, and sunlight exposure. Iodate, which is used to fortify salt in Guatemala, is intrinsically more stable than the iodide used in industrialized nations. The presence of an inadequate amount of iodine in salt suggests an attempt to fortify the salt at the site of production. Inadequate quality control and lax government monitoring and enforcement probably play a role in the genesis of most samples in the range of 5 to 29 ppm. For samples with lower iodine levels, we cannot discount the introduction of unfortified salt into the supply either as contraband from a neighbouring country or from national producers not in compliance with the legal requirements to fortify their product.
In conclusion, the demonstration in recent years of a great variation and general inadequacy in the iodine concentrations of salt in the Guatemalan market [10, 11] was confirmed in this inquiry in a circumscribed region just outside the nation's capital. Within the county, no urban-rural difference was detected, and the presence or absence of a label of iodized salt provided no guidance as to the actual iodine content. The definitive control of iodine-deficiency disorders in this region and in Guatemala as a whole cannot be assured until an sufficient control of the quality of iodized salt is achieved.
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