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In 2011, UIC was assessed in 14, 975 children aged 8-10 years and 13, 932 pregnant women[12] in 902 counties, TV examinations were conducted among 38, 932 children[13], and iodine level was measured in 38, 438 samples of edible salt. In 2014, UIC was assessed in 48, 975 children and 19, 500 pregnant women[12] in 899 counties, TV examinations were conducted among 49, 214 children, and the iodine content was measured in 48, 413 samples of edible salt, as shown in Table 1.
Table 1. Sample Size of Key Survey Indicators in 2011 and 2014
Year Country Children UIC Pregnant women UIC Children TV Edible Salt 2011 902 14, 975 13, 932 38, 932 38, 438 2014 899 48, 975 19, 500 49, 214 48, 413 Results of the two surveys are listed in Table 2 according to the province, where 'Total' is the weighted average of the provinces, taking into account the sixth nationwide population census by the National Statistics Bureau[14].
Table 2. 2011 and 2014 Province Survey Results
In 2011, the MUIC in children and pregnant women were 238.6 and 184.4 µg/L, respectively. In 2014, the MUIC in children and pregnant women were 197.9 and 154.6 µg/L, respectively.
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Overall, the median iodine content of salt decreased between 2014 and 2011 by 5.4 mg/kg, as did the national coverage of iodized and adequately iodized salt (from 98.0% to 96.3% and from 95.3% to 91.5% accordingly). More provinces experienced decreases in coverage of iodized and adequately iodized salt than increases. In 2014, the overall coverage of iodized salt was 96.3%, a slight decrease of 1.7% from the 2011 figure of 98.0%. A total of 19 provinces saw a decline in iodized salt coverage in 2014; in six provinces, the decrease was > 5% (Shanghai, Tianjin, Zhejiang, Shandong, Guangdong, and Jilin). A total of 13 provinces experienced an increase in iodized salt coverage, the biggest rise being 9.9% in Beijing. For adequately iodized salt, the coverage was 91.5% in 2014 compared to 95.3% in 2011, a fall of 3.8%, but still above the goal of 90% for reaching the Chinese IDD Elimination Standard. The coverage of adequately iodized salt decreased in 26 provinces between 2011 and 2014. In 10 provinces, the coverage decreased by > 5%. Six provinces experienced an increase in coverage of adequately iodized salt; the biggest increase was 11.8% in Beijing. Overall, a number of provinces that have achieved IDD elimination by national standards has decreased; 9 provinces had coverage with iodized salt < 95% in 2014 compared to 7 provinces in 2011 and 9 provinces that had coverage with adequately iodized salt < 90% in 2014 compared to 4 in 2011. The median iodine content of edible salt was 25.0 mg/kg in 2014, with a drop of 5.4 mg/kg from the 2011 figure of 30.4 mg/kg. All provinces saw some decrease in their median salt iodine content, with a drop of > 5 mg/kg occurring in 18 provinces, the largest being in Tibet (-11.8 mg/kg). It should be noted that while there were declines in the median iodine content in salt, no province has an iodine content < 22 mg/kg in 2014.
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Urinary Iodine Levels in Children In 2014, the MUIC of Chinese children aged 8-10 years in 32 provinces was 197.9 µg/L, a drop of 40.7 µg/L from the 2011 figure of 238.6 µg/L, bringing China to an optimal iodine status (100-199 µg/L). The MUIC decreased in all but three provinces, one of which was Tianjin where the MUIC increased from 177.9 to 196.8 µg/L. The MUIC was 100-199 µg/L in 19 provinces and 200-299 µg/L in 13 provinces. No province had MUIC > 300 µg/L. In contrast to this, in 2011, the MUIC were 100-199 µg/L in 10 provinces, 200-299 µg/L in 18 provinces, and > 300 µg/L in 4 provinces. In 2014, the proportion of children with a UIC of < 100 µg/L was 15.8%, whereas it was 12.2% in 2011. The proportion of children whose UIC was < 50 µg/L was 4.3% in 2014, which was not much different from the 2011 figure of 3.7%. The proportion of children whose UIC was > 300 µg/L was 18.8% in 2014, a drop of 11% from the 2011 figure of 29.8%. Thus, the overall decline in MUIC increased the proportion of provinces with children MUIC in the adequate range and reduced the proportion of provinces with children MUIC in more than adequate and excess ranges. The proportion of provinces with excessive MUIC was reduced to zero, as shown in Table 3.
Table 3. Children's Urinary Iodine Frequency Distribution in 2011 and 2014
Year < 50 μg/L < 100 μg/L > 300 μg/L 2011 3.70% 12.20% 29.80% 2014 4.30% 15.80% 18.80% Urinary Iodine levels in Pregnant Women Similar to children, the MUIC of pregnant women also decreased between 2011 and 2014 from 184.4 to 154.6 µg/L. In 2014 the MUIC of pregnant women was 150-250 µg/L in 13 provinces; the MUIC in Guangxi, Ningxia, Fujian, Shanghai, and Tibet was 120-130 µg/L; and the MUIC in pregnant women in Inner Mongolia was 111.6 µg/L. In 2011, the MUIC in pregnant women in Guangxi, Fujian, Guangdong, Shanghai, Tianjin, and Tibet was 130-150 µg/L.
Compared with the situation in 2011, the MUIC of pregnant women was more concentrated, the lowest provincial MUIC being > 110 µg/L and the highest provincial MUIC being < 230 µg/L (Table 2).
Children Goiter Rate Based on the results of the B-mode ultrasound examination, the prevalence of goiter among Chinese children was 2.6% in 2014, which was virtually identical to the 2.4% level noted in 2011, a non-significant difference. In 2014, among the goiter rate of children in China, only that in Shandong was > 5% (5.6%). In 2011, among the goiter rate of children in China, only that in Chongqing was > 5% (5.5%). These results were also found to be similar.
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As shown in Table 4, the goiter rate among children in the 200-299 µg/L group was 2.6%, which was higher than that in the 100-199 µg/L group (Z = 33.60, P < 0.05), indicating that the appropriate range of urine iodine in children extended to 100-299 µg/L was not suitable for the general population in China[15].
Table 4. UIC of Children, Median Salt Iodine Level, and Goiter Rate
UIC (μg/L) Iodine Content of Salt (mg/kg) Goiter Rate (%) Sample Size Median Iodine Content Sample Size Goiter Rate < 50 1, 920 25.0 1, 988 2.1 50-99 5, 600 25.0 5, 866 2.1 100-199 17, 142 25.1 17, 707 2.0 200-299 12, 854 25.4 12, 888 2.6 > 300 8, 927 25.4 8, 776 2.7 According to Table 5, there was an U-shaped association between household iodine level in salt or MUIC and the goiter prevalence among children[16]. At an iodized salt level of 5-19.9 mg/kg, the MUIC was found to be within the range of adequate iodine concentration (179.2 µg/L) and also corresponded to the lowest goiter rate (1.9%).
Table 5. Household Salt Iodine Content, Children's MUIC, and Goiter Rate
Household Iodine Level in Salt (mg/kg) Children MUIC (μg/L) Goiter Rate (%) Sample Size MUIC Sample Size Goiter Rate < 5 1, 823 157.2 1, 773 2.4 5-19.9 4, 404 179.2 4, 254 1.9 20-49.9 42, 070 192.6 40, 524 2.3 > 50 111 235.5 106 2.8
doi: 10.3967/bes2018.089
Effect of Reduction in Iodine Content of Edible Salt on the Iodine Status of the Chinese Population
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Abstract:
Objective The aim of this study was to evaluate the impact of the revised Chinese National Standard GB26878-2011 'Iodine Content in Edible Salt' on the iodine status among the Chinese population. Methods In 2011 and 2014, the probability proportionate to size sampling (PPS) was used in each Chinese province to obtain the representative data. In each sampling unit, school children aged 8-10 years and pregnant women were selected. Key indicators included urinary iodine concentration (UIC), thyroid volume (TV), and the iodine content in edible household salt. Results The median urinary iodine concentration (MUIC) decreased between 2011 and 2014 from 238.6 to 197.9 μg/L in school-age children. The number of provinces with iodine excess decreased to zero. The proportion of children whose UIC was > 300 μg/L was 18.8% and decreased to 11% compared with 29.8% in 2011. There was no significant difference in UIC < 50 μg/L between 2014 (4.3%) and 2011 (3.7%) (P > 0.05). The MUIC among pregnant women in 2014 was more concentrated between 110 and 230 μg/L. The goiter rate among children aged 8-10 years was unchanged, both the goiter rate of 2011 and 2014 remaining below 5%, in view of the sustainable elimination of iodine deficiency disorders. Conclusion The National Standard GB26878-2011 'Iodine Content in Edible Salt' that was introduced in March 2012 resulted in an overall improvement in iodine status, reducing the risk of excessive iodine intake in the Chinese population. -
Key words:
- Urinary iodine concentration /
- Thyroid volume /
- PPS method
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Table 1. Sample Size of Key Survey Indicators in 2011 and 2014
Year Country Children UIC Pregnant women UIC Children TV Edible Salt 2011 902 14, 975 13, 932 38, 932 38, 438 2014 899 48, 975 19, 500 49, 214 48, 413 Table 2. 2011 and 2014 Province Survey Results
Table 3. Children's Urinary Iodine Frequency Distribution in 2011 and 2014
Year < 50 μg/L < 100 μg/L > 300 μg/L 2011 3.70% 12.20% 29.80% 2014 4.30% 15.80% 18.80% Table 4. UIC of Children, Median Salt Iodine Level, and Goiter Rate
UIC (μg/L) Iodine Content of Salt (mg/kg) Goiter Rate (%) Sample Size Median Iodine Content Sample Size Goiter Rate < 50 1, 920 25.0 1, 988 2.1 50-99 5, 600 25.0 5, 866 2.1 100-199 17, 142 25.1 17, 707 2.0 200-299 12, 854 25.4 12, 888 2.6 > 300 8, 927 25.4 8, 776 2.7 Table 5. Household Salt Iodine Content, Children's MUIC, and Goiter Rate
Household Iodine Level in Salt (mg/kg) Children MUIC (μg/L) Goiter Rate (%) Sample Size MUIC Sample Size Goiter Rate < 5 1, 823 157.2 1, 773 2.4 5-19.9 4, 404 179.2 4, 254 1.9 20-49.9 42, 070 192.6 40, 524 2.3 > 50 111 235.5 106 2.8 -
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