Iodine status five years after the mandatory salt iodization legislation indicates above requirement: a cross sectional study in Northwest Ethiopia

Iodine is an essential nutrient and its deficiency leads to iodine deficiency disorders (IDDs) [1]. Sever iodine deficiency during pregnancy causes complications like abortion, stillbirth, and malformation and impairs the brain growth and development of children [2, 3]. Iodine deficiency is one of a major nutritional problem and its control is a global public health triumph [4]. Universal salt iodization and fortification of iodine with foods like bread have been showed to have a significant impact on improving iodine status of vulnerable population groups worldwide [1, 5–8].

In Ethiopia, the use of iodized salt for human consumption was first launched in late 1980’s, but interrupted after Eritrea became an independent state [9, 10]. In February 2011 the government of Ethiopia passed a comprehensive legislation which mandated the use of iodized salt for human consumption. The WHO recommends that the coverage of iodized salt utilization at the household level should be above 90% to achieve elimination of iodine deficiency in countries with salt iodization program [11]. However, a nationwide survey in 2014 by Ethiopian Public Health Institute (EPHI) showed a national iodized salt coverage of 88.8% at the household level but the level of iodine in the table salt was adequate in only 53.9% of the households [12]. the 2016 Ethiopian Demographic and Health Survey reported 89.3% households used iodised salt [13]. The proportion of households using adequately iodized salt after introduction of the USI program were 29.7% in Lay Armachiho district [14], 33.2% in Dabat district [15], 28.9% in Gondar town [16], and 26.2% in Shebe Senbo district [17]. High prevalence of goiter [14, 17–21] and median UIC < 100 μg/l [17, 19, 21–23] was also reported across the country pre-and post-mandatory salt iodization in 2011. On the other hand, excessive iodine intake in the Ethiopian Somali regional state has also been reported [24, 25].

The introduction of mandatory iodized salt program did not improve the iodine status of populations in Northwest Ethiopia [14, 16, 18, 22]. A recent study by Abebe et al. in 2016, reported a goiter prevalence of 29.1% in school aged children which indicated iodine deficiency in Dabat District in Northwest Ethiopia [18]. UIC and goiter prevalence in school aged children are both recommended markers of populations’ iodine status [1, 26]. However, UIC is a marker of recent iodine intake, thus suitable to be used to detect recent changes in iodine status of populations while goiter is both a clinical and epidemiological marker that reflects longer term iodine deficiency [26, 27]. There is no any UIC data on school aged children in Dabat district.

Hence, the current study assessed the iodine status in Dabat District and assess agreement between two markers of iodine status of the population namely the median UIC and prevalence of goiter in school-age (6–12 years) children.

Our study is the first to assess iodine status using two recommended population markers of iodine status in northwest Ethiopia. We found that the population was classified as above requirements based on the median UIC but severe iodine deficient based on the goiter prevalence.

The median UIC in school aged children in the current study was above requirements and higher than studies done post-salt iodization program in Ethiopia [17, 19, 22, 23]. The reason why the median UIC was higher than other areas may be due to variation in dietary sources of iodine and the coverage of iodised salt use in study populations. However, the intake of the main food sources of iodine is low in Ethiopia [13] in general and the study area [14] in particular. The variation in the dietary sources of iodine is unlikely to cause such substantial variations in the median UIC across the studies. Therefore, the difference in the coverage and utilization of iodized salt could be the cause of disparity in the median UIC across different regions in the country. The geographical location may affect access to iodised salt in populations. The current study includes both urban and rural areas in terms of location, and both highlands and lowlands in altitude, however, studies in other areas were conducted mainly in rural and populations living in highlands.

Based on the current study the salt iodization program was effective in combating iodine deficiency in the study population. Universal salt iodization also improves iodine status of other countries [1, 11, 26]. Iodine intake was optimal in the majority of participants included in the study, one-third of them were found with excessive iodine intake above 300 μg/l. Excessive iodine intake during early childhood may potentially lead to iodine-induced thyroid dysfunction; both hypothyroidism and hyperthyroidism [33, 34]. A higher concentration of iodine from a poorly controlled salt iodisation program may be the source of excess iodine in these population. Besides, other sources of dietary iodine including water need to be explored in the food-chain of the study area to monitor intake and ensure that the population is not adversely exposed to excessive levels of iodine.

The prevalence of goiter is comparable with similar studies [14, 18] in the study area which reported iodine deficiency post-iodine fortification. However, there is a discrepancy in reporting iodine status in the same population at the same point in time among these two epidemiological markers of iodine status: prevalence of goiter and median UIC. Discrepancy in classifying iodine status in populations between goiter prevalence and median UIC also reported elsewhere [27, 35]. Median UIC indicates recent intake and it is a sensitive marker to detect recent changes in iodine status in the population. Conversely, the prevalence of goiter indicates medium to long term iodine intake and may not be sensitive to recent changes in the iodine status of populations [11, 26, 27]. The current study was conducted 5 years post mandatory iodine fortification in Ethiopia and presumably the two markers need to agree on assessing the degree of iodine status in the population. However, the severe iodine deficiency by goiter and above requirements by median UIC shows the iodised salt was introduced only recently. Intake of goitrogenic foods other than iodine deficiency may lead to goiter in populations [36, 37]. Moreover, assessment of goiter by palpation is subjective and prone to bias. However, the assessors were qualified, and training was given before commencement of data collection. It appears that total goiter rate may not be an appropriate epidemiological tool to monitor iodine status of the population shortly after universal salt iodization program.

The WHO, UNICEF, and ICCIDD jointly recommend the level of iodine should be 15–40 ppm at a household level and 20–40 ppm in the retails to fulfil iodine requirement of the population. Moreover, to demonstrated successful use of iodised salt in the study population, above 90% of households, should use adequately iodised salt which is above 15 ppm and bellow 40 ppm [26]. Even though the population in the present study were above requirement based on the median UIC, salt iodine level was adequate only in 30.7% of households. In this study, 29.1% of school-age children had excessive iodine intake > 300 μg/l and the median UIC was significantly higher in children from households with the level of salt iodine content was ≥15 ppm. This shows salts with iodine content ≥15 ppm may have extreme high concentrations of iodine that needs a quantitative measurement to confirm the exact iodine concentration in table salts. However, we have used a rapid test kits to measure iodine concentration in the salts and classify adequacy of iodine qualitatively. This warrants assessment of salt iodine contents using a quantitative marker such as a titration method. This finding is consistent with other study in the same population which reported 33.2% households used adequately iodised salt post fortification [15]. Higher proportion of inadequate salt iodine content among households in the study area indicates a possibility of fluctuations in iodised salt supply in the community or availability of non-iodised salt in the local market or poor utilization of iodised salt including use of open containers to store salt, exposing the salt to sunlight and storage of salt for long period of time at the household level. This warrants further research measuring salt iodine level at retail shops and salt manufacturing sites. Even though we did not assess the iodine intake using iodine specific food frequency questionnaire, the intake of main sources of foods including fish, eggs and dairy products are low in the population and a close monitoring of the utilization of iodized salt in the study area is warranted.

The study is a cross-sectional survey and might not show the trend overtime in iodine status since the introduction of iodine fortification program in the study population. The study employed a multistage cluster sampling procedure but did not adjust the sample size using the design effect to minimize the clustering effect in the inferential statistics. However, the calculated sample size is adequate to measure median urinary iodine concentration in the study population. There may be intra-assessor variation on measurement of goiter in school aged children. We used a semi-quantitative method to assess the level of iodine in the salt and may not exactly quantify the concentration of iodine in the salt.

The iodine status of the study population is classified as above requirements by median UIC in school-age children but severe iodine deficiency by goiter prevalence. Regular monitoring of the level of household iodised salt and median UIC in school-age children and other vulnerable groups like pregnant and breastfeeding women is recommended. Continuous monitoring of iodine status of the population helps to detect potential harms of both iodine deficiency and excess. Studies investigating causes of goiter other-than iodine deficiency and the iodine content of staple foods and drinking water in the study area are also warranted. Further research investigating the agreement between median UIC and goiter prevalence in classifying iodine status of populations with various iodine status is warranted.