Iodine deficiency disorders after a decade of universal salt iodization in a severe iodine deficiency region in China.
Background & objectives: Universal salt iodization (USI) was
implemented in all counties of China in 1995. This study was undertaken
to assess the status of iodine deficiency disorders control and
prevention after 10 years of implementation of USI in a severe iodine
deficiency region in China.
Methods: Thirty primary school were selected in Gansu province utilizing cluster sampling methodology for the years 1995 and 2005. In each selected school, 40 children aged 8-10 yr were randomly selected for thyroid and IQ examination, and urinary samples were collected from 12. On the spot casual urine samples and salt samples were collected from a subset of children included in the study. In 2005, casual urine samples were also collected from 50 pregnant and lactating women in each cluster. Effect of health education was studied by a combination method of giving questionnaires to and observing students and families.
Results: The total goiter rates (TGR) were found to be 13.5 and 38.7 per cent in 2005 and 1995 respectively. The medians urinary iodine excretion levels of children were 191.8 and 119.9 [micro]g/l in 2005 and 1995. The median urinary iodine excretion level of women was 161.9 [micro]g/l. The mean intelligence quotient (IQ) was 96.9 in 2005 significantly more than that in 1997 (P<0.05). The health education pass rate of children and women were 21.1 and 51.1 per cent respectively.
Interpretation & conclusion: After ten years of universal salt iodization (USI), iodine nutrition of people improved and the current iodine nutrition status of population was adequate. Decrease in TGR and increase in IQ showed that IDD control and prevention had made great progress through ten years USI, salt iodization played the key role in IDD control and prevention for sustained elimination of IDD, the programme of USI and other measures like health education should be persisted and enforced.
Key words Goiter--health education--intelligence quotient (IQ)--iodine deficiency disorders (IDD)--salt iodization--urinary iodine excretion (UIE)
Elementary school students
(Food and nutrition)
Elementary school students (Health aspects)
Iodized salt (Health aspects)
Pregnant women (Health aspects)
Iodine deficiency diseases (Risk factors)
Iodine deficiency diseases (Care and treatment)
|Publication:||Name: Indian Journal of Medical Research Publisher: Indian Council of Medical Research Audience: Academic Format: Magazine/Journal Subject: Biological sciences; Health Copyright: COPYRIGHT 2009 Indian Council of Medical Research ISSN: 0971-5916|
|Issue:||Date: Oct, 2009 Source Volume: 130 Source Issue: 4|
|Product:||Product Code: E197200 Students, Elementary|
|Geographic:||Geographic Scope: China Geographic Code: 9CHIN China|
Iodine is an essential ingredient for the synthesis of thyroid
hormones. Iodine deficiency (ID) causes goiter and different forms of
physical and mental retardation. Iodine deficiency disorders (IDD)
affect the poor, pregnant woman and preschool children (1,2). Normal
levels of thyroid hormones are required for neuronal migration and
myelination of the foetal brain, and lack of iodine irreversibly impairs
brain development (3). Severe ID during pregnancy increases risk for
stillbirths, abortions, and congenital abnormalities (4,6).
Cross-sectional studies of moderate to severely iodine-deficient
children have generally reported impaired intellectual function and fine
motor skills. Two meta-analyses estimated that populations with chronic
ID experience a reduction in intelligence quotient (IQ) of 12.5-13.5
points (7,8). Iodized salt has been recognized as the most effective way
to control and prevent IDD. Universal salt iodization (USI) has been
remarkably successful in many countries. Over 30 countries have achieved
the goal of USI (>90% of households using iodized salt), and many
others are on track (1). USI was implemented in China in all counties in
1995. The initial iodization level was set at 50 mg/kg (50 ppm), later
reduced in 2000 to 35 ([+ or -]15) ppm after national monitoring of
urinary iodine concentration showed this intake to be excessive; the
medians of urinary iodine of school children, at provincial level, were
over 300 [micro]g/l in 18 and 14 provinces in 1997 and 1999,
respectively (9,10). IDD is a significant public health problem in China
(11). Monitoring of iodized salt was carried out at county level one
time per year in higher iodized salt coverage counties and two time per
year in lower iodized salt coverage counties. A national survey in 1995
found the prevalence of goiter among school children to be [+ or -] 10
per cent in 27 of 30 provinces (12). This study was in conducted 1995
when USI was implemented and a decade later in 2005 with the objectives
to assess the effects of USI on the status of IDD in a severe iodine
deficiency region in China.
Material & Methods
Study area: Gansu province in China was classified in 1995 as having a severe level of IDD according to WHO/UNICEF/ICCIDD criteria (12) with a total goiter rate in school children of 38.7 per cent and median urinary iodine level of 119.9 [micro]g/l. It is located in the west part of China. Gansu has twelve cities and two autonomous prefectures and 87 counties (cities and districts) directly under its jurisdiction. The province total area is 454,400 square kilometers and its population is 26.0625 million at the end of 2006 (13). Gansu is a landlocked, mountainous area with little rain that is far from sea. In more than 90 per cent samples of drinking water the iodine contents was less than 10 [micro]g/l (14) in surveillance in 1999. 850,000 patients had visible goiter, cretins were 20000 according to investigation in Gansu province.
The school enrollment rate of children in the age group of 8-10 yr was more than 90 per cent in Gansu province and hence, a school based study was conducted in 1995 and then in 2005 using the same methods. The 30 clusters sampling methodology recommended by WHO/UNICEF/ICCIDD1 was utilized for selecting the clusters. Thirty schools were selected and in each school, 40 children aged 8-10 yr were selected randomly for thyroid examination and IQ test; urinary samples were collected from 12 of these 40 children randomly (9,10) as the number of urinary samples can represent the urinary iodine level of the people (15). The goiter was graded according to the criteria recommended by the joint WHO/UNICEF/ICCIDD in 1994 (16) (grade 0, no goiter; grade 1, thyroid palpable but not visible; and grade 2, thyroid visible with neck in normal position). When in doubt, the immediate lower grade was recorded. The intra- and inter-observer variation was controlled by repeated training and random examinations of goiter grades by another author. The results were recorded in a pre-designed questionnaire. The sum of grades 1 and grades 2 provided the total goiter rate (TGR) of the study population (16). If the requisite number of children could not be completed from the selected cluster/school, then the nearest adjointing school was included to complete the total number of subjects to be covered in the cluster.
Intelligence quotient (IQ) of children included in the study was tested with Combined Raven's Test Rural and City in China (17,18). The Ravens was designed to reduce the biases that language differences can have on measuring IQs. It allows children to show pattern-recognition, attention to details, memory, and spatial reasoning. This test is suitable for group measurement and is less likely to be affected by environment, culture, and acquired knowledge (19). The Chinese norm was applied to calculate the age-adjusted IQ value for each child (17). The IQ value of superexcellence was >130, excellence 120-129, upper middling 110-119, middling 90-110, below middling 80-89, verge mental retardation 70-79, mental retardation [greater than or equal to]69, and a prevalence of mentally retarded children in normal group was 2.2 per cent according to Chinese norm (17).
Before the study, women groups and parents of children were explained about the study and consents were obtained. The study protocol was approved by ethical committee of Gansu Center for Diseases Control and Prevention.
Statistical analysis: Results were analyzed by SPSS (version 10.0). Medians were used to describe the iodine concentration in urine and salt. Chi square test was used to compare prevalence of goiter.
Goitre: A total of 1241 children in the age group of 8-10 yr were included in 2005 & (49.8 % boys 50.2% girls). The total goiter prevalence was found to be 13.4 per cent in boys and 13.5 per cent in girls. The TGR was found to be 13.5 per cent in 2005. It was observed that the total goiter rate increased with the increase in age (Table I). Compared with the study of 1995, the TGR decreased from 38.7 to 13.5 per cent (P<0.05).
Urinary iodine concentration: The proportion of children with urinary iodine excretion (UIE) levels 0-19.9, 20.0-49.9, 50.0-99.9 and [greater than or equal to]100 [micro]g/l was 2.0, 8.4, 14.0 and 75.6 per cent in 2005. The median UIE of the study children was found to be 191.8 [micro]g/l in 2005 and 119.9 [micro]g/l in 1995 (Table II). The median UIE of pregnant and lactating women was 172.2 and 159.2 161.9 [micro]g/l (Table III).
Salt iodine level: Median level of iodine in salt was 23.5 ppm in 1995 and 30.0 ppm in 2005. A total of 32.5 and 2.8 per cent salts had iodine content 5-20 ppm and the consumption rates of qualified iodized salt (20-50 ppm) were 59.9 and 96.6 per cent respectively in 1995 and 2005, reflecting the quality of iodized salt has been improved greatly (Table IV). The consumption rate of qualified iodized salt was 55.5 per cent in 1995 and 88.9 per cent in 2005.
Intelligence quotient: IQ of 1102 children included in the study was tested in 2005. The mean IQ was 96.9 (Table V). The mean IQ of children has been improved compared with that of 91.0 in 1997 (23) (P<0.05). But IQ values still showed a positive skewed distribution.
Health education: The health education pass rate of children and women was 21.1 and 51.1 per cent respectively (Table VI) indicating health education measures were very week.
Salt iodization has been an effective, safe and convenient measure to control and prevent IDD. After ten years of USI, the consumption rate of qualified iodized salt increased in Gansu province, but did not reach the standard of National IDD elimination (>90%). The total goiter rate increased with the increase in age. May be at the beginning of USI, the consumption rate of qualified iodized salt was very low, the older children (born in 1995) have higher risk of exposure to iodine deficiency than younger children (born in 1996 and 1997). The iodine nutrition of people has improved. The median urinary iodine excretion levels of children and women has reached the criterion recommended by the WHO1 and the current iodine nutrition status of population was adequate. Though the TGR decreased greatly from the year 1995, the TGR of children was still 13.5 per cent. One reason is that the TGR represent the chronic iodine deficiency while the urinary iodine excretion (UIE) levels indicate the current iodine nutrition. The size of the thyriod gland changes inversely in response to alterations in iodine intake, with a lag interval that varies from a few months to several years, depending on many factors. These include the severity and duration of iodine deficiency, the type and effectiveness of iodine supplementation, age, sex, and possible additional goitrogentic factors (1). Another reason was the consumption rate of disqualified iodized salt was still high. The IQ values had improved from 91.0 in 1997 to 96.9 in 2005, but the brain development of children was still damaged (3).
After ten years of USI , IDD control and prevention had made great progress in Gansu province. Iodine nutrition of people had reached to an appropriate level. Salt iodization played key role in IDD control and prevention. In order to achieve the goal of IDD sustained elimination, the Universal Salt Iodization Programme should be persisted and the quality of iodized salt provided to the beneficiaries should be monitored continuously. In addition, emphasis need to be given on health education.
This work was supported by National Support Project for Science and Technology in China (2007BAC29B03) and the Project of National Natural Science Foundation of China (40675077).
Received January 28, 2008
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Reprint requests: Dr Yibo Wang, College of Earth & Environment Sciences, Lanzhou University, Lanzhou Gansu 73000, P.R. China
Yanling Wang (***), Zhongliang Zhang (dagger]), Pengfei Ge (**), Yibo Wang (*) & Shigong Wang ([double dagger])
(*) The Gansu Key Laboratory of Arid Climate Change & Reducing Disaster, College of Earth & Environment Sciences, Lanzhou University, (**) Gansu Center for Diseases Control & Prevention, ([dagger]) The First People Hospital of Lanzhou City & ([double dagger]) College of Atmospheric Sciences, Lanzhou University, Lanzhou Gansu, PR China
Table I. Results of thyroid examination of children (8-10 yr) in 2005 Age Number Goiter grade (%) Total group goiter (yr) 0 I II rate (%) 8 375 89.3 10.4 0.3 10.7 9 439 87.9 11.6 0.5 12.1 10 427 82.7 16.4 0.9 17.3 Total 1241 86.5 12.9 0.5 13.5 Table II. Urinary iodine excretion levels of children (8-10 yr old) Year n Median urinary Frequency distribution of urinary iodine concen- iodine excretion level (%) tration ([micro]/l) 0-19.9 20-49.9 50-99.9 1995 362 119.9 0.6 5.2 11.1 2005 356 191.8 2.0 8.4 14.0 Year Frequency distribution of urinary iodine excretion level (%) [greater than or equal to] 100 [micro]g/l 1995 83.1 2005 75.6 Table III. Urinary iodine excretion levels of women in 2005 Median urinary Frequency distribution Population group Number iodine concentra- of urinary iodine tion ([micro]g/l) excretion level (%) 0-19.9 20-49.9 Pregnant women 487 172.2 2.5 7.6 Lactating women 1264 159.2 3.4 10.1 Total 1751 161.9 3.1 9.4 Population group Frequency distribution of urinary iodine excretion level (%) 50-99.9 [greater than or equal to] 100 [micro]g/l Pregnant women 15.4 74.5 Lactating women 16.5 70.0 Total 16.2 71.3 Table IV. Results of iodized salt estimation at household level in 1995 and 2005 Year N Iodine median Non-iodized 5-20 ppm of iodized salt rate (%) salt (ppm) (<5p pm) (%) 1995 1200 23.5 7.1 32.5 2005 1147 30.0 7. 7 2.8 Year Consumption Qualified rate of qulified iodized iodized salt (%) salt (%) 1995 55.5 59.9 2005 88.9 96.6 Table V. Intelligence quotient (IQ) level and its distribution of school-age children in 2005 Frequency Year n distribution (%) IQ (mean [+ or -] SD) <69 70-79.9 2005 1102 96.9 [+ or -] 15.6 4.6 8.8 Theory -- 100 [+ or -] 15 2.2 6.7 Year Frequency distribution (%) 80-89.9 90-99.9 110-119.9 120-129.9 2005 17.9 48.0 13.5 6.8 Theory 16.1 50.0 16.1 6.7 Year Frequency distribution (%) [greater than or equal to] 130 2005 0.4 Theory 2.2 distribution (19) Table VI. The outcome of health education of children and women in 2005 Population Number Knowing IDD Knowing iodized Mean group harm (%) salt can prevent score IDD (%) Children 555 24.3 48.5 34.6 Women 133 15.8 45.9 56.3 Population Pass rate group (%) Children 21.1 Women 51.1
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