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Preplanned Studies: A Cross-Sectional Survey of Iodized Salt Usage in Dining Establishments — 13 PLADs, China, 2021–2022

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  • Summary

    What is already known about this topic?

    The National Iodine Deficiency Disease Surveillance system is exclusively focused on monitoring cooking salt used within households. Currently, there is a lack of nationally representative data on the use of iodized salt in dining establishments.

    What is added by this report?

    This study evaluated 7,889 salt samples obtained from dining establishments located in 13 provincial-level administrative divisions across China. The findings indicated that coverage rate of iodized salt (CRIS) and the consumption rate of adequately iodized salt (CRAIS) were found to be 95.2% and 90.2%, respectively. Further, 880 samples were classified as iodized salt and 804 as adequately iodized salt. In coastal areas, the CRIS and CRAIS showed a significant decrease to 77.1% and 70.5%, respectively, when compared to the inland regions (P<0.01).

    What are the implications for public health practices?

    The data compiled could potentially fill the void in the national data concerning the use of iodized salt in dining establishments throughout China. It is of the utmost importance to increase the awareness of restaurant operators, particularly those located in coastal areas, about the benefits of iodine supplementation. Moreover, they should be encouraged to use adequately iodized salt.

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  • [1] Wang ZY, Zhou JZ, Jia XD. Is the cooking salt safe in China? Assessment of chemical contaminants in cooking salt. Biol Trace Elem Res 2019;191(2):512 − 6. http://dx.doi.org/10.1007/s12011-019-1646-5CrossRef
    [2] Gorstein JL, Bagriansky J, Pearce EN, Kupka R, Zimmermann MB. Estimating the health and economic benefits of universal salt iodization programs to correct iodine deficiency disorders. Thyroid 2020;30(12):1802 − 9. http://dx.doi.org/10.1089/thy.2019.0719CrossRef
    [3] Bhat S, Marklund M, Henry ME, Appel LJ, Croft KD, Neal B, et al. A systematic review of the sources of dietary salt around the world. Adv Nutr 2020;11(3):677 − 86. http://dx.doi.org/10.1093/advances/nmz134CrossRef
    [4] Ministry of Health of the People’s Republic of China. GB 26878-2011 National food safety standard for iodine content of table salt. Beijing: Standards Press of China, 2012. (In Chinese). 
    [5] Wang ZY, Jin W, Zhu ZN, Cui XY, Song Q, Shi ZH, et al. Relationship of household cooking salt and eating out on iodine status of pregnant women in environmental iodine-deficient coastal areas of China. Br J Nutr 2020;124(9):971 − 8. http://dx.doi.org/10.1017/S000711452000207XCrossRef
    [6] Wang ZY, Zang JJ, Shi ZH, Zhu ZN, Song J, Zou SR, et al. Iodine status of 8 to 10 years old children within 20 years following compulsory salt iodization policy in Shanghai, China. Nutr J 2019;18(1):63. http://dx.doi.org/10.1186/s12937-019-0491-xCrossRef
    [7] Cui YS, Wang Y, Hou CC, Zhang DD, Zheng P, Chen ZJ, et al. Iodine in household cooking salt no longer plays a crucial role in iodine status of residents in Tianjin, China. Eur J Nutr 2022;61(5):2435 − 49. http://dx.doi.org/10.1007/s00394-021-02792-wCrossRef
    [8] Shi M, Yu WS, Li ZT, Dong JH. Investigation on iodine nutrition level of pregnant women in coastal area of Qingdao from 2016 to 2020. J Community Med 2022;20(4):181 − 5. http://dx.doi.org/10.19790/j.cnki.JCM.2022.04.01 (In Chinese). CrossRef
    [9] Luo LY. Survey on iodine nutrition level of population in coastal and inland areas of Guangxi. J Environ Health 2020;37(7):648-51.
    [10] Wang Z, Xu J. Iodine in foods. Beijing: Peking University Medical Press. 2021. https://book.kongfz.com/385721/6044678773/. (In Chinese). https://book.kongfz.com/385721/6044678773/
    [11] Mao GM, Zhu WM, Mo Z, Wang YY, Wang XF, Lou XM, et al. Iodine deficiency in pregnant women after the adoption of the new provincial standard for salt iodization in Zhejiang Province, China. BMC Pregnancy Childbirth 2018;18(1):313. http://dx.doi.org/10.1186/s12884-018-1952-5CrossRef
    [12] Chen ZH, Wu JN, He M, Lin ZH, Wang MH, He M, et al. Effects of universal salt iodization on iodine nutrition status of pregnant women in Fujian coastal areas. Strait J Prev Med 2010;16(5):1-2. https://d.wanfangdata.com.cn/periodical/hxyfyxzz201005001. (In Chinese). https://d.wanfangdata.com.cn/periodical/hxyfyxzz201005001
    [13] Cao HY, Wang SC, Li XJ. Analysis of iodized salt monitoring results in Dongguan food service units in 2008. Chin J Public Health Manag 2009;25(6):650. http://qikan.cqvip.com/Qikan/Article/Detail?id=32598009. (In Chinese). http://qikan.cqvip.com/Qikan/Article/Detail?id=32598009
  • TABLE 1.  Characteristics of the surveyed areas and dining establishments.

    PLADsCounties (N)Residents
    (million)
    Per capita income
    (thousand
    CNY/year)
    Number of
    dine-out
    places
    Types of dine-out placesService type
    TotalCoastalInlandCanteenMSRSRTable mealFast food
    Anhui100108.429.661011025025053278
    Fujian10375.136.6600100250250394206
    Gansu100103.424.7600102198300488112
    Hebei100105.030.8600100250250420180
    Henan100109.026.4601100249252461140
    Inner Mongolia100103.240.1600100242258496104
    Jiangsu10469.956.860010025025050793
    Liaoning10284.537.8601100250251500101
    Shandong101006.756.2601101253247466135
    Shanxi110115.328.666011226128758476
    Sichuan100104.629.660010025025057624
    Xinjiang100103.727.9603104237262390213
    Yunnan100106.537.1606103223280495111
    Total1311911275.435.57,8821,3323,1633,3876,3091,573
    Abbreviation: PLADs=provincial-level administrative divisions; MSR=medium-sized restaurant; SR=small restaurant; CNY=Chinese Yuan.
    Download: CSV

    TABLE 2.  Coverage rates for IS and AIS and iodine content at dining establishments by PLAD.

    PLADsISAIS
    NCR (%)Median (P25, P75) (mg/kg)NCR (%)
    Anhui60499.021.7 (20.1, 23.3)57293.8
    Fujian58998.224.2 (23.0, 25.4)57595.8
    Gansu600100.026.6 (24.1, 29.6)56293.7
    Hebei53889.724.3 (21.9, 26.4)51185.2
    Henan59298.525.0 (22.8, 27.7)55592.4
    Jiangsu59599.224.5 (21.8, 26.9)56694.3
    Liaoning56193.524.5 (21.9, 26.9)52387.2
    Inner Mongolia58797.725.2 (23.3, 27.2)56193.3
    Shandong38163.423.4 (20.6, 26.0)33455.6
    Shanxi65699.427.7 (25.4, 29.8)59990.8
    Sichuan59799.526.9 (24.9, 28.8)58397.2
    Xinjiang60299.828.1 (25.2, 31.1)57595.4
    Yunnan60499.725.8 (24.1, 27.6)59197.5
    Total7,50695.225.3 (22.8, 27.7)7,10790.2
    Abbreviation: PLADs=provincial-level administrative divisions; IS=iodized salt; AIS=adequately iodized salt; CR=coverage rate.
    Download: CSV

    TABLE 3.  Coverage rates of IS and AIS based on location, types of dining establishments, and types of services.

    VariableISAISTotal salt sample
    NCR (%)χ2PNCR (%)χ2PN%
    Coastal or inland areas962.6<0.001584.2<0.001
    Coastal88077.180470.51,14114.5
    Inland6,62698.36,30393.56,74185.5
    Types of dine-out places2.40.300.20.93
    Canteen1,26895.21,20290.21,33216.9
    MSR2,99994.82,84790.03,16340.1
    SR3,23995.63,05890.33,38743.0
    Service types3.00.080.20.66
    Table meal5,99595.05,68490.16,30980.0
    Fast food1,51196.11,42390.51,57320.0
    Abbreviation: MSR=medium-sized restaurant; SR=small restaurant; IS=iodized salt; AIS=adequately iodized salt; CR=coverage rate.
    Download: CSV

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A Cross-Sectional Survey of Iodized Salt Usage in Dining Establishments — 13 PLADs, China, 2021–2022

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Summary

What is already known about this topic?

The National Iodine Deficiency Disease Surveillance system is exclusively focused on monitoring cooking salt used within households. Currently, there is a lack of nationally representative data on the use of iodized salt in dining establishments.

What is added by this report?

This study evaluated 7,889 salt samples obtained from dining establishments located in 13 provincial-level administrative divisions across China. The findings indicated that coverage rate of iodized salt (CRIS) and the consumption rate of adequately iodized salt (CRAIS) were found to be 95.2% and 90.2%, respectively. Further, 880 samples were classified as iodized salt and 804 as adequately iodized salt. In coastal areas, the CRIS and CRAIS showed a significant decrease to 77.1% and 70.5%, respectively, when compared to the inland regions (P<0.01).

What are the implications for public health practices?

The data compiled could potentially fill the void in the national data concerning the use of iodized salt in dining establishments throughout China. It is of the utmost importance to increase the awareness of restaurant operators, particularly those located in coastal areas, about the benefits of iodine supplementation. Moreover, they should be encouraged to use adequately iodized salt.

  • 1. National Health Commission Key Laboratory of Trace Element Nutrition, National Institute for Nutrition and Health, Chinese Center for Disease Control and Prevention, Beijing, China
  • 2. Science and Technology Department, Chinese Center for Disease Control and Prevention, Beijing, China
  • Corresponding author:

    Jing Xu, dqfbczsys@163.com

    Online Date: August 25 2023
    Issue Date: August 25 2023
    doi: 10.46234/ccdcw2023.141
  • 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.

    PLADsCounties (N)Residents
    (million)
    Per capita income
    (thousand
    CNY/year)
    Number of
    dine-out
    places
    Types of dine-out placesService type
    TotalCoastalInlandCanteenMSRSRTable mealFast food
    Anhui100108.429.661011025025053278
    Fujian10375.136.6600100250250394206
    Gansu100103.424.7600102198300488112
    Hebei100105.030.8600100250250420180
    Henan100109.026.4601100249252461140
    Inner Mongolia100103.240.1600100242258496104
    Jiangsu10469.956.860010025025050793
    Liaoning10284.537.8601100250251500101
    Shandong101006.756.2601101253247466135
    Shanxi110115.328.666011226128758476
    Sichuan100104.629.660010025025057624
    Xinjiang100103.727.9603104237262390213
    Yunnan100106.537.1606103223280495111
    Total1311911275.435.57,8821,3323,1633,3876,3091,573
    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).

    PLADsISAIS
    NCR (%)Median (P25, P75) (mg/kg)NCR (%)
    Anhui60499.021.7 (20.1, 23.3)57293.8
    Fujian58998.224.2 (23.0, 25.4)57595.8
    Gansu600100.026.6 (24.1, 29.6)56293.7
    Hebei53889.724.3 (21.9, 26.4)51185.2
    Henan59298.525.0 (22.8, 27.7)55592.4
    Jiangsu59599.224.5 (21.8, 26.9)56694.3
    Liaoning56193.524.5 (21.9, 26.9)52387.2
    Inner Mongolia58797.725.2 (23.3, 27.2)56193.3
    Shandong38163.423.4 (20.6, 26.0)33455.6
    Shanxi65699.427.7 (25.4, 29.8)59990.8
    Sichuan59799.526.9 (24.9, 28.8)58397.2
    Xinjiang60299.828.1 (25.2, 31.1)57595.4
    Yunnan60499.725.8 (24.1, 27.6)59197.5
    Total7,50695.225.3 (22.8, 27.7)7,10790.2
    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).

    VariableISAISTotal salt sample
    NCR (%)χ2PNCR (%)χ2PN%
    Coastal or inland areas962.6<0.001584.2<0.001
    Coastal88077.180470.51,14114.5
    Inland6,62698.36,30393.56,74185.5
    Types of dine-out places2.40.300.20.93
    Canteen1,26895.21,20290.21,33216.9
    MSR2,99994.82,84790.03,16340.1
    SR3,23995.63,05890.33,38743.0
    Service types3.00.080.20.66
    Table meal5,99595.05,68490.16,30980.0
    Fast food1,51196.11,42390.51,57320.0
    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.

    • 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 (57). 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 (89) 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.

    • No conflicts of interest.

    • 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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