Iodine Deficiency,  in China

 
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TABLE 1. Urinary iodine concentrations in 10-year-old school-children in 10 large Chinese cities

 

City	N	Median iodine concentration (Hg/L)
Beijing	1,226	137.3
Shanghai	1,427	71.3
Wuhan	1,074	178
Jinan	1,175	100.3
Shenyang	1,153	109.8
Xian	1,196	178
Harbin	1,178	95.4
Zhengzhou	1,200	77
Hefei	1,190	75.4
Fuzhou	1,195	57

TABLE 2. Effects of iodized salt on the control of endemic goitre in 7- to 14-year-old children

 

Location	Duration of consumption	% reduction in goitre prevalence
Provinces
Jiangxi	1982-92	21.0±7.6
Shandong	1993-94	20.7±11.3
Cities
Jianou, Fujian	1984-92	47.0±9.5
Shenyang, Lioning	1978-87	44.8±7.1
Counties
Shangzhi, Heilongjioang	1983-87	31.4±4.3
Xide, Sichuan	1977-82	31.9±2.5
Guangrao, Shandong	1987-91	15.0±10.9

 

Manufacture and use of iodized salt

Different types of salt are used as the substrate for iodized salt, depending on the sources available in specific areas. The major types of salt in China include sea salt, lake salt (solar salt), and mined salt. There are 109 salt plants in China, with an annual production capacity of 800 million tons of iodized salt. According to the Ministry of Health, in 1995 the total production reached 639 million tons, of which 600 million tons were sold. Most plants adopted the spraying method for fortification of salt with iodine, which caused considerable loss of iodine because of the high temperature during spraying. However, the facilities in all 109 plants were renovated in 1996 with financial support from the World Bank and other agencies. Improvements in packaging technology were completed by the end of 1997.

Since 1990 potassium iodate (KIO₃) has replaced potassium iodide (KI) for iodization of salt in China.

National regulations require the iodine content of iodized salt to be no less than 30 mg/kg at the production level, no less than 25 mg/kg at the market level, and no less than 20 mg/kg at the household level. In order to reach these criteria, the actual level of fortification during salt processing must be 40 mg/kg.

Preliminary studies have shown, however, that the iodine content of iodized salt decreases continuously during the whole process from the salt plant to the consumer, depending on manufacturing methods, packaging materials, and storage time. The shortest half-life was found to be 12 weeks [12]. In general practice, the storage time is about one month in the plant and three months in the marketing system (provinces and counties). However, in some remote areas, the storage period could be as long as six months.

In order to examine the quality of the iodized salt supply, the Ministry of Health recently conducted a nationwide survey after one year of compulsory manufacture and use of iodized salt. The results showed that 80% of the salt used at the household level contained iodine, but only 51% of the samples met the requirement for iodine content (20 mg of iodine per kilogram of salt). At 20 of 22 national monitoring points for iodine-deficiency disorders where iodized salt has been used for a longer period, the salt samples did not meet the required iodine concentration [13]. A case study in Shandong province demonstrated that the iodine content of iodized salt decreased progressively from 75% in the fortification plant, to 49% in county warehouses, to 8% in the local market, and finally to 7.6% in the households [5]. This decrease indicates that in addition to iodine loss, other factors may account for the low levels of iodine found in the salt purchased by consumers, including low levels of iodine added during processing, the use of cheap, uniodized salt (especially in remote, poor areas), and the use of locally produced crude salt as a substrate.

Cooking loss is another major reason for the failure of control of iodine-deficiency disorders by iodized salt. Since recipes and cooking procedures vary in different parts of the country, and the number of dishes using salt is so large, it is difficult to know the overall iodine loss during cooking, and so far very little information is available. Preliminary unpublished data from the Institute of Nutrition and Food Hygiene of the Chinese Academy of Preventive Medicine show that the loss of iodine during conventional Chinese cooking ranges from 50% to 70%.

At present the Chinese recommended daily intake of iodine is 150 to 200 mg per person per day, and the criteria for elimination of iodine-deficiency disorders in children aged 7 to 14 years are a prevalence of endemic goitre of less than 5% and urinary iodine content above 100 mg/L. According to the nationwide nutrition survey conducted in 1992, the mean daily intake of salt was 13.8 g per person, indicating that the daily intake of iodine should have been 276 mg per person based on the government fortification standard of 20 mg/kg. Taking all these factors into account, the dietary intake situation is far from satisfactory.

 

Major problems in iodine fortification

The Chinese government is determined to reach the goal of elimination of iodine-deficiency disorders by the year 2000 by using iodized salt as the major control measure in the general population. The national iodized salt programme has been implemented since early 1955, but there are major problems in enforcing it. These problems include the use of uniodized salt in remote rural areas combined with the lack of adequate processing technology in these areas, which results in iodized salt of poor quality that does not meet the national standard; an unsatisfactory system for monitoring the quality of iodized salt, which provides no guarantee that the salt used by consumers will meet the national standard; the lack of knowledge of the public health significance of iodine-deficiency disorders and the importance of iodized salt for its control among the marketing staffs of companies that process and sell salt; the loss of iodine during storage and cooking; and the absence of nationwide systematic studies on the effectiveness of iodized salt in controlling iodine-deficiency disorders (although its effectiveness in individual areas has been established). The appropriate concentration of iodine in salt for the Chinese population has not been established, given the characteristics of salt manufacturing, transportation, storage, and cooking. There is much to do to achieve the government’s goal of eliminating iodine-deficiency disorders in China by the year 2000.