Abstract
Background
Iodine deficiency disorder (IDD) is a major public health problem in Ethiopia. The availability of adequate iodized dietary salt at the household level is immensely important. Hence, this review aimed to estimate the pooled prevalence of adequate iodine concentration level of iodized dietary salt at the household level and its associated factors in Ethiopia.
Methods
We searched the literature using electronic databases (PubMed/Medline, Google Scholar, Science Direct, and Embase) and gray literature from January 9, 2022, to February 25, 2022. The rapid test kit was used to measure the adequacy of iodine level of dietary salt. The quality of studies was assessed using Joanna Briggs Institute critical appraisal tool. Heterogeneity between studies was checked using I2 test statistics and publication bias was checked using funnel plot and Egger’s statistical test at a 5% significance level. A random-effects model was employed to estimate the pooled prevalence of the outcome variable and its determinants in Ethiopia.
Results
The search identified 149 studies of which 18 studies were included with a total of 10,556 participants. The pooled prevalence of adequate iodine levels of iodized salt in Ethiopia was 44.37% (95% CI: 35.85-52.88). Women who had formal education (adjusted odds ratio (AOR) = 1.99 (95% CI: 1.47–2.48)), good knowledge of women (AOR = 2.14, 95% CI: 1.36–3.36), packed iodized salt (AOR = 3.85 (95% CI: 1.88–7.87)) and storage of iodized salt at home for less than 2 months (AOR = 2.66 (95% CI: 2.11–3.35) were the significant factors.
Conclusion
This review suggests that the pooled prevalence of adequate iodine levels was low. Our finding highlights the need for considering the educational status, knowledge, and duration of salt storage to enhance the prevalence of adequate levels of iodized salt at the national level.
Introduction
Iodine is present in the body in scarce amounts (1) and is an essential micronutrient that is required for the production of thyroid hormone which is vital for immune response, growth, and brain development of the fetus, infants, and young children (1, 2, 3). Also, it has an important role in a wide range of functions including academic performance (4, 5), physical development of child and women’s health, quality of human life, and the economic productivity of adults (6, 7, 8). However, inadequate intake of iodine leads to insufficient production of thyroid hormone which causes stillbirth, abortion, impaired growth, cretinism, and stunting (3, 9). These adverse effects are collectively known as iodine deficiency disorders (IDD) (1, 6, 10).
According to World Health Organization (WHO) report, approximately one-third of the world’s population lives in areas where sources of iodine are insufficient, and around 29.8% (241 million) school-age children, are among the vulnerable groups and are estimated to have insufficient intake of iodine from the total school-age children, 58 million of them are living in African (11). The global control of iodine deficiency through a universal salt iodization program has been introduced in many countries over the past 30 years (1, 12). Despite this and ongoing interventions, many populations in the world remain at risk of iodine deficiency (4, 13).
In Ethiopia, great progress has been made toward the elimination of iodine deficiency through the provision of household iodized salt (14). However, many potential barriers have been identified that reduce the iodine content of iodized salt and some of them include educational status, salt washing, sunlight, heat, packing, knowledge, and poor handling practices (15, 16). Adequate data are not available about coverage of the adequacy of iodine content in household iodized salt and its associated factors at the national level in Ethiopia. Therefore, this systematic review and meta-analysis aimed to estimate the pooled prevalence of adequate iodine content in household iodized salt and its associated factors in Ethiopia.
Methods
Search strategy and selection criteria
The authors did a systematic review and meta-analysis using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines (17). We searched exhaustively different databases like PubMed/Medline, Google Scholar, Science Direct, Embase, and unpublished literatures from January 9, 2022, to February 25, 2022. All studies were searched using the keywords (Prevalence) OR (magnitude) OR (epidemiology) OR (level) AND (associated factors) OR (determinants) AND (iodine concentration) AND (iodized salt) AND (household) AND (Ethiopia).
Eligibility criteria
Inclusion criteria
The two investigators (T M E and R H K) independently reviewed the retrieved articles carefully. Those studies conducted in Ethiopia, published in English, and original researches containing the prevalence and associated factors of the adequate iodine content of iodized salt in the household were included in this study. In addition, articles that used a rapid test kit (RTK) to assess the iodine content of iodized salt were considered as inclusion criteria.
Exclusion criteria
Studies with incomplete data on the outcome variable were excluded in this review. Moreover, studies that used measures other than the WHO, United Nations Children's Fund (UNICEF), and International Council for Control of Iodine Deficiency Disorders (ICCIDD) recommendation for adequacy of iodine concentration were excluded from the analysis.
Outcome measures
The primary outcome of this study was dichotomized as adequate or inadequate iodine level of iodized salt. The WHO, UNICEF, and ICCIDD joint recommendation was used to measure the outcome variable if the RTK result of iodine level of dietary salt of 15 ppm and above was considered as adequate and inadequate if the iodine level of dietary salt was less than 15 ppm. Furthermore, the secondary outcomes considered in this review were the associated factors that related to reducing the level of iodine in iodized dietary salt.
Data extraction
Data extraction from studies was done by two independent reviewers (T M and R H). Disagreements between reviewers were resolved through discussion. We used a standardized data extraction form, Microsoft excel sheet format, to collect the information from all the eligible studies. All the selected studies were summarized and recorded with the following domains: name of the first author, publication year, region, study setting and design, sample size, response rate, prevalence rate, and quality score (Table 1).
Summary of included studies to assess the iodine concentration level of iodized salt at household level in Ethiopia, 2021.
| Author | Publication year | Regions | Setting | Sample size | Included | Outcome | Response rate | Prevalence | JBI-Score |
|---|---|---|---|---|---|---|---|---|---|
| Bazezew et al. (3) | 2018 | Addis Ababa | Urban | 549 | 544 | 184 | 99.1 | 33.8 | Low risk |
| Fereja et al. (32) | 2018 | Oromia | Rural | 356 | 351 | 138 | 98.6 | 64.8 | Low risk |
| Tariku & Mazengia (33) | 2019 | Amhara | Both | 714 | 700 | 443 | 98 | 63.3 | Low risk |
| Ajema et al. (20) | 2020 | SNNPR | Urban | 875 | 875 | 509 | 100 | 58.2 | Low risk |
| Mesele et al. (34) | 2014 | Amhara | Rural | 698 | 694 | 694 | 99.4 | 29.7 | Low risk |
| Hailu et al. (35) | 2016 | Oromia | Urban | 422 | 393 | 114 | 93.1 | 29 | Low risk |
| Abebe et al. (22) | 2017 | Amhara | Both | 714 | 705 | 234 | 98.7 | 33.2 | Low risk |
| Anteneh et al. (15) | 2017 | Amhara | Rural | 1194 | 1194 | 683 | 100 | 57.4 | low risk |
| Mekonnen et al. (23) | 2018 | Amhara | Urban | 500 | 492 | 341 | 98.4 | 69.3 | Low risk |
| Gebremariam et al. (21) | 2013 | Amhara | Urban | 848 | 810 | 234 | 95.5 | 28.9 | Low risk |
| Gebremichael et al. (36) | 2020 | Amhara | Both | 596 | 576 | 162 | 96.6 | 28.1 | Low risk |
| Desta et al. (19) | 2019 | Tigray | Both | 318 | 292 | 51 | 91.8 | 17.5 | Low risk |
| Kumma et al. (16) | 2018 | SNNPR | Urban | 441 | 440 | 166 | 99.8 | 37.7 | Low risk |
| Teka (25) | 2020 | Addis Ababa | Urban | 423 | 415 | 266 | 98.1 | 63.8 | Low risk |
| Bulli et al. (37) | 2020 | Oromia | Rural | 603 | 596 | 364 | 98.8 | 61.1 | Low risk |
| Gebriel et al. (38) | 2014 | Benishangul | Urban | 395 | 395 | 79 | 100 | 20 | Low risk |
| Dinka et al. (26) | 2021 | Oromia | Both | 476 | 470 | 140 | 98.7 | 29.8 | Low risk |
| Mesfin et al. (20) | 2020 | Amhara | Both | 620 | 614 | 448 | 99.03 | 73 | Low risk |
Quality assessment
The Joanna Briggs Institute (JBI) checklist (18) was used as a guideline to assess the quality of each articles reviewed. The JBI scores assigned to each reviewed article that range from 0 if none of the criteria were met to 8 if all criteria were met, then the sum of the study represented the overall quality of a study. Then studies were rated as low risk or good quality when it scored 4 and above included in the analysis.
Statistical analysis
Meta-analysis was performed using STATA version-14.0 software after importing the prepared data from the Microsoft Excel sheet. Meta-analysis of the pooled prevalence of adequate iodine concentration level was carried out using a random effect model with a 95% CI. Heterogeneity among the reported prevalence of studies was checked by using the I2 test. Publication bias was also assessed objectively by performing Egger's correlation and Begg's regression intercept tests at a 5% significance level and subjectively by funnel plot through visual assessment for its asymmetry. Subgroup analysis was carried out using study setting (categorized as urban, rural, and both), study period, and sample size. Moreover, sensitivity analysis was performed to see the influence of each study on the overall effect size.
Results
We identified 149 studies from different databases and other sources. After we removed the duplicate studies, 79 studies were excluded because they were irrelevant for this study. Then, the remaining 24 full-text studies were assessed for eligibility and 6 studies were excluded after reading the full article because they did not use WHO definition for adequacy of iodine level for iodized dietary salt. Finally, 18 studies were eligible and included for computing the pooled prevalence of the outcome of variable with a total of 10,556 study participants. The flow diagram of the study search and selection process are depicted in Fig. 1. The distribution of the studies in the regional states of Ethiopia were Amhara (8), Oromia (4), SNNPR (2), Addis Ababa (2), Benishangule Gumz (1), and Tigray (1). The detailed characteristics of the studies are shown in Table 1.
A PRISMA flow chart explaining the selection of primary studies for systematic review and meta-analysis.
Citation: European Thyroid Journal 11, 4; 10.1530/ETJ-22-0066
Meta-analysis
In this review, the overall pooled prevalence of adequate iodine level of iodized dietary salt in households in Ethiopia was 44.37% (95% CI: 35.85–52.88) and the prevalence ranges from 17.5 (19) to 73% (20) (Fig. 2). A random effect model was used and the result of the heterogeneity test was I2= 98.9% (P < 0.0001). Publication bias was assessed subjectively by observing the funnel plot which was found to be a symmetrical distribution of included studies (Fig. 3) and objectively by applying the Egger test (P = 0.71). Both methods revealed the absence of publication bias among studies. In addition, subgroup analysis was done by study setting (categorized as urban, rural, and both), study period, and sample size. Furthermore, the result of sensitivity analysis revealed that there is no single study that affects the pooled prevalence of adequate iodine level of dietary iodized salt in the household (Fig. 4).
Forest plot revealing the pooled prevalence of adequate iodine concentration in dietary iodized salt at the household level in Ethiopia.
Citation: European Thyroid Journal 11, 4; 10.1530/ETJ-22-0066
Funnel plot of 95% CI for publication bias to assess the pooled prevalence of adequate concentration of dietary iodized salt.
Citation: European Thyroid Journal 11, 4; 10.1530/ETJ-22-0066
Output of sensitivity analysis of included studies for this review.
Citation: European Thyroid Journal 11, 4; 10.1530/ETJ-22-0066
Subgroup analysis
Subgroup analysis was conducted based on study setting, study period, and sample size. Based on study design, the prevalence of adequate iodine concentration in household iodized salt of rural part of the country was found to be 45.79%. Using the study period, the prevalence of adequate iodine concentration in household iodized salt among studies conducted in 2017 and before was 39.17 (Table 2).
Summary of subgroup analysis of the prevalence of adequate iodine concentration iodized dietary salt in household in Ethiopia.
| Variables | Number of articles | Prevalence of adequate iodine | I2 (P-value) |
|---|---|---|---|
| Number of studies | ES (95% CI) | ||
| Study setting | |||
| Urban | 8 | 42.58 (29.86–55.30) | 98.8% (<0.001) |
| Rural | 4 | 53.21 (37.42–68.99) | 98.7% (<0.001) |
| Both | 6 | 40.84 (23.09–58.57) | 93.3% (<0.001) |
| Study period | |||
| ≤2017 | 13 | 39.17 (30.06–48.28) | 98.7% (<0.001) |
| >2017 | 5 | 57.85 (42.07–73.64) | 98.8% (<0.001) |
| Sample size | |||
| ≤600 | 10 | 39.35 (27.66–51.05) | 98.7% (<0.001) |
| >600 | 8 | 73.00 (69.48–76.51) | 99.0% (<0.001) |
| Overall | 18 | 44.36 (35.85–52.88) | 98.9% (<0.001) |
Factors associated with iodine level of iodized dietary salt
All authors have analyzed the potential determinants of iodine concentration level of iodized salt in household in Ethiopia from eight studies (15, 16, 21, 22, 23, 24, 25, 26). Knowledge and educational status of the women, home storage duration of iodized dietary salt at home, and packed iodized salt were the significant associated factors.
Knowledge of women
The result of five articles (15, 21, 22, 24, 26) showed that women who had good knowledge for iodine were 2.14 times more likely to have adequate iodine level of iodized dietary salt at the household than those women having poor knowledge (AOR = 2.14, 95% CI: 1.36–3.36) (Fig. 5).
Forest plot depicting the association of adequate iodine concentration in dietary iodized salt with knowledge of women.
Citation: European Thyroid Journal 11, 4; 10.1530/ETJ-22-0066
Educational status of women
The pooled result of six included articles (15, 16, 22, 23, 24, 26) revealed that women who had formal education were 1.99 times more likely to have adequate iodine concentration level in the iodized salt at their own home than those women who had no formal education (Fig. 6).
Forest plot revealing the association of adequate iodine concentration in dietary iodized salt with educational status of women.
Citation: European Thyroid Journal 11, 4; 10.1530/ETJ-22-0066
Packed/covered iodized salt
Regarding the availability of packed iodized dietary salt, the pooled result of five studies (15, 16, 21, 22, 26) showed that the level of adequate iodine in the iodized salt with cover/packing was 3.85 times higher than unpacked/uncovered iodized salt (Fig. 7).
Forest plot showing the association of adequate iodine concentration in dietary iodized salt with packed iodized salt.
Citation: European Thyroid Journal 11, 4; 10.1530/ETJ-22-0066
Storage duration of iodized salt at home
Moreover, the result from four studies (15, 21, 25, 26) revealed that storage duration was the other significant factor that affects the adequacy of iodine level. The odds of storage of iodized salt for less than 2 months at home was 2.66 times more likely to have adequate iodine concentration in iodized salt than iodized salt kept for 2 months and beyond at home (Fig. 8).
Forest plot revealing the association of adequate iodine concentration in dietary iodized salt with duration of iodized salt storage at home.
Citation: European Thyroid Journal 11, 4; 10.1530/ETJ-22-0066
Discussion
Universal salt iodization is the major approach to eliminate IDD especially in developing countries like Ethiopia (11). This systematic review and meta-analysis reviewed the prevalence of adequate iodine level in iodized salt and associated factors in Ethiopia. This review revealed that the pooled prevalence of adequate level of iodine in household iodized salt was low at 44.37% (95% CI: 35.85–52.88). To eliminate iodine deficiency disorder, the WHO recommended that the prevalence of adequate iodine content in dietary salt in the household must be equal to or greater than 90% (27). This shows that Ethiopia is still far from reaching achieving world health recommendations of dietary salt with adequate iodine levels at the national level.
Regarding subgroup analysis, in this review, the prevalence of adequate levels of iodine in dietary salt in 2017 and before was 39.17 % (95% CI: 30.06–48.28) lower than studies conducted after 2017 (57.85 (95% CI: 42.07–73.64)). This could be the presence of continuous community awareness creation on the importance of iodized salt. Moreover, the prevalence of adequate iodine level in dietary salt at the household level was higher in rural settings (53.21% (95% CI: 37.42–68.99)) than in urban settings (42.58% (95% CI: 29.86–55.30)). This might be due to great efforts that were made for the rural communities through health extension packages by the government of Ethiopia.
Besides, having formal educational status and good knowledge of women were the significant factors that affect the level of iodine content in dietary salt in line with the study conducted in India (28), this might be because educated and knowledgeable women may have the culture of practicing proper storage and utilization of iodized dietary salt at the household.
This review showed that using packed/covered salt was significantly associated with an adequate level of iodine in dietary salt than using unpacked salt in the household. This finding is consistent with the studies conducted in Poland (29) and Iran (30). This might be due to the fact that unpacked iodized salt may lose the iodine content because of different environmental factors. And according to our study, finding the content of iodine in iodized salt storage of iodized salt at the home beyond 2 months increase the loss of iodine content of dietary salt. This finding is in line with the studies conducted in Iran (30) and China (31), and this might be due to the increment of the loss of iodine content in iodized salt over time. In conclusion, continuous monitoring of the quality of iodized salt, proper utilization of iodized salt, and creating community awareness on how to use and the benefits of iodized dietary salt would have a better impact on achieving WHO standards and the elimination of IDD. Finally, the government of Ethiopia and stakeholders should increase the coverage and access for iodized dietary salt with adequate iodine concentration at the household level and strengthen salt legislation enforcement.
Supplementary materials
This is linked to the online version of the paper at https://doi.org/10.1530/ETJ-22-0066.
Declaration of interest
The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported.
Funding
This work did not receive any specific grant from any funding agency in the public, commercial, or not-for-profit sector.
Availability of data and materials
The data set used for this review is available upon reasonable request from the corresponding author.
Author contribution statement
T M E has contributed to the conceptualization and design. T M E and R H K performed the literature search, data extraction, analysis, and interpretation of the data. T M E wrote the first draft of the manuscript. T M E, R H K, S H, M M, T M, D S and G A revised the paper. All authors have read and approved the final manuscript.
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