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deficiency in China
Iodine Deficiency, in China
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.
