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Universal salt iodization has been established as a safe and effective method for the control of iodine deficiency disorders (IDDs) (1-2). Despite the annual National Iodine Deficiency Disease Surveillance, which began in 1995, only household cooking salt is analyzed. Yet, as the culture of eating out and ordering takeaway becomes more common, the contribution of household cooking salt to overall salt consumption has declined (3). Furthermore, current “Regulations on Salt Iodization to Mitigate the Risks of Iodine Deficiency” specify only that iodized salt is to be used in food products made and sold in deficient areas, leaving a gap in guidelines related to restaurant use. Hence, it is vital to scrutinize and assess the use of iodized salt (IS) and adequately IS (AIS) in dining establishments. At this stage, there remains a lack of nationwide, representative data on IS use in such settings. In response to this, the study in question employed a multiple-sampling technique to amass 7,889 salt samples from restaurants across 13 provincial-level administrative divisions (PLADs) in China, aiming to provide a nationally representative snapshot. Findings indicate that the coverage rate of IS (CRIS) and consumption rate of AIS (CRAIS) are 95.2% and 90.2%, respectively. However, when focused on coastal regions, the CRIS and CRAIS dropped to 77.1% and 70.5%, respectively, marking a significant difference from inland regions (P<0.01). This discrepancy suggests a need to enhance IDD awareness training for restaurant personnel in coastal areas to promote the procurement of IS.
This cross-sectional study was carried out from 2021 to 2022 across 13 PLADs of China, which were strategically divided into three regions: East, Central, and West. We executed a random selection of 4–5 PLADs from each region. Further, we subdivided each PLAD into five geographical divisions: east, west, south, north, and central. From each geographical division, two counties were randomly selected to serve as our sampling units. Each chosen county was then further dissected into five sampling areas, also based on geographical orientation. Subsequently, a town or sub-district with low water iodine levels was randomly picked from each particular sampling area. Within each chosen town or sub-district, we randomly selected two institutional canteens (either corporate or public) along with five medium-sized restaurants (MSRs) and five small restaurants (SRs). Ultimately, a total of 60 dining locations per county were selected, culminating in a comprehensive evaluation of 130 counties across China.
A 50-gram salt sample was meticulously extracted from the top, middle, and bottom sections of a salt package acquired from a selected dining establishment. The extraction process entailed using a moisture-free, airtight plastic bag. The salt iodine content (SIC) was then evaluated following the standards stipulated by the “General Test Method for Salt Industry Determination of Iodine” (GB/T 13025.7-2012). Salt that was iodized with KIO3 was scrutinized utilizing direct titration, while salt iodized with KI or other compounds was analyzed via redox titration. Salt with an SIC less than 5 mg/kg was termed non-IS (NIS). AIS was characterized as SIC within an allowed fluctuation range, defined as a deviation of ±30% from the average iodine content level in edible salt (4). The term “CRIS” was used to denote the ratio of salt samples boasting an iodine content equal to or greater than 5 mg/kg to the total samples tested, while “CRAIS” denoted the ratio of AIS samples to the total number tested.
The data for this study were inputted into Microsoft Excel 2016 (Microsoft Corporation, Redmond, Washington, USA) and subsequently transferred to SAS 9.4 for Windows (SAS Institute, Cary, NC, USA) to facilitate analysis. A test to verify a normal distribution was carried out on continuous data; data that were skewed were represented via median (quartile range). To compare groups with skewed data, nonparametric tests (including the Wilcoxon and Kruskal-Wallis tests) were utilized. Count and percentage, used to express qualitative data, were tested for proportional differences using the Chi-squared test. All of the statistical tests used were two-tailed, with P<0.05 being indicative of a statistically significant difference.
This study evaluated 131 counties across 13 PLADs in China, encompassing a population of 75,374,000 individuals with a per capita income of 35,508 Chinese Yuan (CNY). Among these counties, 19 (14.5%) are located along the coast in the PLADs of Liaoning, Fujian, Shandong, and Jiangsu. The details of the sample size are presented in Table 1.
PLADs Counties (N) Residents
(million)Per capita income
(thousand
CNY/year)Number of
dine-out
placesTypes of dine-out places Service type Total Coastal Inland Canteen MSR SR Table meal Fast food Anhui 10 0 10 8.4 29.6 610 110 250 250 532 78 Fujian 10 3 7 5.1 36.6 600 100 250 250 394 206 Gansu 10 0 10 3.4 24.7 600 102 198 300 488 112 Hebei 10 0 10 5.0 30.8 600 100 250 250 420 180 Henan 10 0 10 9.0 26.4 601 100 249 252 461 140 Inner Mongolia 10 0 10 3.2 40.1 600 100 242 258 496 104 Jiangsu 10 4 6 9.9 56.8 600 100 250 250 507 93 Liaoning 10 2 8 4.5 37.8 601 100 250 251 500 101 Shandong 10 10 0 6.7 56.2 601 101 253 247 466 135 Shanxi 11 0 11 5.3 28.6 660 112 261 287 584 76 Sichuan 10 0 10 4.6 29.6 600 100 250 250 576 24 Xinjiang 10 0 10 3.7 27.9 603 104 237 262 390 213 Yunnan 10 0 10 6.5 37.1 606 103 223 280 495 111 Total 131 19 112 75.4 35.5 7,882 1,332 3,163 3,387 6,309 1,573 Abbreviation: PLADs=provincial-level administrative divisions; MSR=medium-sized restaurant; SR=small restaurant; CNY=Chinese Yuan. Table 1. Characteristics of the surveyed areas and dining establishments.
Among the 7,882 salt samples gathered, 95.2% were iodized, with notable variation across PLADs (χ2=1592.59, P<0.01). Of the 376 identified NIS, 58.5% were found in Shandong Province, 16.5% in Hebei Province, and 10.4% in Liaoning Province. A total of 7,107 AIS were discovered, with a consumption rate of 90.2% also showing significant provincial variation (χ2=983.73, P<0.01). The median iodine content of IS was 25.3 mg/kg, presenting significant provincial variation as well (χ2=1903.81, P<0.01; Table 2).
PLADs IS AIS N CR (%) Median (P25, P75) (mg/kg) N CR (%) Anhui 604 99.0 21.7 (20.1, 23.3) 572 93.8 Fujian 589 98.2 24.2 (23.0, 25.4) 575 95.8 Gansu 600 100.0 26.6 (24.1, 29.6) 562 93.7 Hebei 538 89.7 24.3 (21.9, 26.4) 511 85.2 Henan 592 98.5 25.0 (22.8, 27.7) 555 92.4 Jiangsu 595 99.2 24.5 (21.8, 26.9) 566 94.3 Liaoning 561 93.5 24.5 (21.9, 26.9) 523 87.2 Inner Mongolia 587 97.7 25.2 (23.3, 27.2) 561 93.3 Shandong 381 63.4 23.4 (20.6, 26.0) 334 55.6 Shanxi 656 99.4 27.7 (25.4, 29.8) 599 90.8 Sichuan 597 99.5 26.9 (24.9, 28.8) 583 97.2 Xinjiang 602 99.8 28.1 (25.2, 31.1) 575 95.4 Yunnan 604 99.7 25.8 (24.1, 27.6) 591 97.5 Total 7,506 95.2 25.3 (22.8, 27.7) 7,107 90.2 Abbreviation: PLADs=provincial-level administrative divisions; IS=iodized salt; AIS=adequately iodized salt; CR=coverage rate. Table 2. Coverage rates for IS and AIS and iodine content at dining establishments by PLAD.
The coastal regions’ CRIS and CRAIS were observed to be less than 80%, significantly lower compared to those of inland regions (P<0.01; Table 3). There was a slightly lower CRIS found in MSRs in comparison to canteens and SRs, although the difference was not statistically significant (P=0.30). In canteens, SRs, and MSRs, the CRAIS exceeded 90% with no significant differences observed (P=0.93). The CRIS and CRAIS in fast food-serving establishments were marginally higher than those providing table meal service, even though the difference was not statistically meaningful (P>0.05).
Variable IS AIS Total salt sample N CR (%) χ2 P N CR (%) χ2 P N % Coastal or inland areas 962.6 <0.001 584.2 <0.001 Coastal 880 77.1 804 70.5 1,141 14.5 Inland 6,626 98.3 6,303 93.5 6,741 85.5 Types of dine-out places 2.4 0.30 0.2 0.93 Canteen 1,268 95.2 1,202 90.2 1,332 16.9 MSR 2,999 94.8 2,847 90.0 3,163 40.1 SR 3,239 95.6 3,058 90.3 3,387 43.0 Service types 3.0 0.08 0.2 0.66 Table meal 5,995 95.0 5,684 90.1 6,309 80.0 Fast food 1,511 96.1 1,423 90.5 1,573 20.0 Abbreviation: MSR=medium-sized restaurant; SR=small restaurant; IS=iodized salt; AIS=adequately iodized salt; CR=coverage rate. Table 3. Coverage rates of IS and AIS based on location, types of dining establishments, and types of services.
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The findings of this study indicated that the CRIS and CRAIS in dining-out venues were 95.2% and 90.2%, respectively. It was observed that these measurements were notably lower in coastal regions as compared to inland areas. However, no significant variance in CRIS and CRAIS was discovered among canteens, MSRs, and SRs. Furthermore, there was no statistically significant distinction in CRIS and CRAIS between establishments offering table meals and those providing fast food.
According to China’s “Criteria for Elimination of Iodine Deficiency Disorders (GB16006-2008)” introduced in 2008, a household CRIS of ≥95% and a CRAIS >90% are requisite for IDD elimination. Hence, the values for household CRIS, CRAIS, and SIC have been incorporated into the national IDD control project as critical indicators for monitoring and evaluating iodine nutrition. However, due to rapid economic progress and increased speed of contemporary life, eating out, buying takeout, and consuming packaged foods are becoming the norm in China. Interestingly, in certain economically advanced areas of the country, household cooking salt no longer significantly influences the population’s iodine status (5–7). Two surveys conducted in Shanghai illuminated that household salt iodine intake failed to impact the iodine status of pregnant women (5) and children (6). Further, a monitoring study in Tianjin from 2016 to 2020 unveiled no correlation between the CRIS, CRAIS, and SIC of household cooking salt and iodine status indices within the population (specifically urinary iodine concentration and thyroid volume) once confounding factors were adjusted for (7). The said study’s authors proposed that the IDD control project’s household salt-related indicators should be amended to accommodate other indicators, such as SIC in school canteens (7). This current study involves an assessment of 7,889 salt samples taken from restaurants nationwide and effectively addresses the deficiency of IS monitoring data on such establishments. Furthermore, this study lays the groundwork for subsequent adjustments of IS monitoring indicators by providing essential data.
Multiple studies (8–9) investigating household salt usage have discovered that the CRIS and the CRAIS in coastal regions were noticeably lower than those in inland areas. A research project in Qingdao City found that household CRIS and CRAIS stood at 88.2% and 86.2%, respectively, failing to meet the elimination criteria for IDD (8). A similar study in Guangxi Zhuang Autonomous Region indicated significantly lower CRIS and CRAIS (75.59% and 63.25%) in coastal households than in their inland counterparts (9).
Given this data, it was important to examine if a substantial difference existed in IS usage between inland and coastal restaurant settings. This study found that the CRIS and CRAIS in coastal restaurants were merely 77.1% and 70.5%, respectively, a marked difference to the 98.3% and 93.5% in inland establishments.
Interviews suggested that missing or inaccurate information may be contributing to this discrepancy, with one such misconception being the unnecessary consumption of iodized salt due to the regular intake of seafood in coastal areas. It should be noted that while coastal residents generally consume more seafood, the iodine content in seafood is only marginally higher than that in land-based animal foods (10). Thus, the iodine intake tends to be lower in coastal regions.
The highest quantities of iodine in seafood are generally found in specific types of seaweed, but consumption of seaweed is quite minimal. Furthermore, the presence of private salt farms in some coastal regions encourages the use of non-iodized coarse sea salt, resulting in a reduced CRIS.
A study by Mao et al. (11) found that the urinary iodine concentration in pregnant women living in Zhejiang Province’s coastal areas was 107.54 μg/L, significantly lower than that of pregnant women in inland areas (152.54 μg/L). It was speculated that this iodine deficiency was linked to the low local CRIS. Similar research by Chen et al. pointed out that the median urinary iodine of pregnant women in rural coastal areas of Fujian (134.9 μg/L) fell short of the World Health Organization’s recommendation (12).
To decrease the risk of iodine deficiency among residents of coastal areas, notably pregnant women and lactating mothers, it is crucial to raise not only household CRIS rates but also restaurant operators’ awareness of iodine supplementation. Encouraging restaurant operators to purposely purchase and utilize AIS can be a significant step in this direction.
A prior study indicated a higher incidence of CRAIS in large or MSRs compared to SRs (13). This was initially attributed to the deficient regulatory mechanisms within SRs, insufficient food safety awareness and improper management. However, the current study reveals no significant variance in CRIS and CRAIS distribution across diverse dining establishments. This can be reasoned through several factors. First, the recent years have seen an increase in coverage of food safety awareness and educational programs, thus augmenting the health consciousness of individuals responsible for SRs or those involved in procurement. Second, the introduction of efficient regulatory mechanisms has significantly mitigated the circulation of substandard IS in the marketplace.
This study possesses certain limitations. Due to its cross-sectional design, evaluating the temporal relationship between various factors was unattainable, thereby complicating the inference of causation. Additionally, a number of elements influencing the concentration of IS, inclusive of storage methods, purchase dates, and individual health consciousness, were not incorporated in the survey.
To our understanding, this constitutes the first substantial study examining the utilization of IS in dining establishments, thus yielding national-level representative data. This research scrutinized the usage of IS in 7,882 dining venues across 13 PLADs in China, thereby filling an existing void regarding IS data in such establishments within the country. The employment of IS in China’s dining places was deemed satisfactory. Moreover, CRIS and CRAIS in Canteens, MSRs, and SRs matched the criteria set for IDD eradication. Notwithstanding, the CRIS and CRAIS in coastal regions were significantly inferior to those in inland areas. Consequently, augmenting IDD knowledge among restaurant personnel in coastal areas is vital, enhancing their consciousness about purchasing IS. Similarly, it is crucial to bolster local supervision and surveillance mechanisms to suppress the distribution of non-compliant IS in the market.
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No conflicts of interest.
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Centers for Disease Control and Prevention in Anhui Province, Fujian Province, Gansu Province, Hebei Province, Henan Province, Jiangsu Province, Liaoning Province, Inner Mongolia Autonomous Region, Sichuan Province, Xinjiang Uygur Autonomous Region, the Institute for Endemic Disease Control in Shandong Province, Shanxi Province, and Yunnan Province.
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