Iodine status and goiter prevalence after 40 years of salt iodisation in the Kangra District, India
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《美国医学杂志》
1 Department of Human Nutrition, All India Institute of Medical Sciences, Ansari Nagar, New Delhi, India
2 Health and Family Welfare Training Center, Kangra, District Kangra, Himachal Pradesh, India
Thirty primary schools were selected in district Kangra utilizing the population proportionate to size cluster sampling methodology in the year 2004. A total of 6939 children were included in the study. The clinical examination of the thyroid of each child was conducted. On the spot casual urine sample and salt samples were collected from a 'sub set of' children included in the study. The Total goiter rate (TGR) was found to be 19.8%. The median Urinary iodine excretion level was 200 μg/l and only 64% of the salt samples had the stipulated level of iodine. The findings of the present study revealed that current iodine status of population is adequate, however, TGR showed mild iodine deficiency (chronic), and there is a need of continued monitoring the quality of iodised salt provided to the beneficiaries under the Universal salt iodisation programme in order to achieve the goal of elimination of Iodine deficiency disorders from district Kangra.
Keywords: Goiter; Iodine deficiency disorders; Salt iodisation; Urinary iodine excretion
District Kangra in Himachal Pradesh, India is a known iodine deficiency endemic area.[1],[2],[3] A survey conducted in 1956 reported a goiter prevalence of 55% in the district.[4],[5] Subsequently, an intervention trial was conducted during 1955 to 1961 in the district Kangra resulted in reduction of goiter prevalence in the range of 20-30%. In 1973, a repeat survey was conducted and it was found that the continued salt iodisation programme further reduced the TGR to 8.5-9.1% in the district Kangra.[4] In 1999, another repeat survey was conducted. It was revealed that the prevalence of goiter as 12.1%.[6] Authors conducted a study during year 2004 with the objectives to assess the prevalence of IDD after 40 years of supply of iodised salt in the district Kangra and to estimate the iodine content of salt consumed by the population so that the state government can strengthen the existing Universal salt iodisation programme activities in the district, if required.
Materials and Methods
A school based study was conducted during January to March 2004 in district Kangra. The children in the age group of 8-10 years were included. The 30 cluster sampling methodology as recommended by the WHO/UNICEF/ICCIDD, was utilized for selecting the clusters. Keeping in view, the anticipated prevalence of iodine deficiency as 15%, a confidence interval of 95%, relative precision of 10% and a design effect of 3, a total sample size of 6531 was calculated.[7] In each cluster, 227 children in the age group of 8 to 10 years were included in the study. A total of 6939 children were included in the study.
The school enrollment rate of children in the age group of 8-10 years was more than 90% in district and hence, the school based approach was adopted.[8] All the primary schools in the district with their total enrollment were enlisted and thirty schools were selected for the detailed study utilizing the population proportionate to size cluster sampling methodology.[9] The identified schools were visited and the subjects were briefed about the objectives of the study during the school assembly. The clinical examination of the thyroid of each child was conducted. The goiter was graded according to the criteria recommended by the joint WHO/UNICEF/ICCIDD. When in doubt, the investigators recorded the immediate lower grade. The intra and inter observer variation was controlled by repeated training and random examinations of goiter grades by first author. The results were recorded in a pre-designed questionnaire. The sum of grades 1 and 2 provided the TGR of the study population.[7] If the requisite number of children could not be completed from the selected cluster/school, then the nearest adjoining school was included to complete the total number subjects to be covered in the cluster.
The study was linked with annual school health examination survey which was conducted in school routinely for which the informed consent was obtained.
On the spot casual urine sample were collected from every 10th child included in the study. Plastic bottles with screw caps were provided to children for the urine samples. The samples were stored in the refrigerator until analysis. The UIE levels were analysed using the wet digestion method.[10] A pooled urine sample was prepared for Internal Quality Control (IQC) assessment. The IQC sample was analysed 25 times with standards and blank in duplicate. This IQC sample having a known concentration range of iodine content was run with every batch of test samples. If the results of the IQC sample was within the range (ie. Mean ± 2SD) then the test was deemed in control and if the results were outside the range, then the whole batch was repeated. Salt was collected from every 13th child included in the study. The children were provided with auto seal polythene pouches with an identification slip. They were requested to bring four tea spoons of salt (about 20 g) from their family kitchen and the iodine content of salt samples was analysed by spot testing kit method.[11] The salt and urine samples were analysed by a trained technician.
Constraints of the Study
The intra and inter observer variation in goiter examination was controlled by repeated training and random examination of goiter grade by expert. However, inspite of all the precautions for the quality control, a possibility existed for misclassification of goiter grade I.
The non response rate was less than 1% as it was part of annual health examination and no intervention was conducted.
Results
A total of 6939 children in the age group of 8-10 years were included in the present study. Nearly 52.2% of the children were males and 47.8% were females. The age wise distribution of children according to the various grades of goiter is depicted in [Table - 1]. The total goiter prevalence was found to be 20.3% in boys and 19.2% in girls. It was observed that the total goiter rate increased with the increase in age. The TGR was found to be 19.8% (CI 21.78-17.82) in the present study. It has been documented that if more than 5% of the school aged children are suffering from goiter, the area should be classified as endemic to iodine deficiency.[7] The findings of the present study revealed that in district Kangra, mild iodine deficiency existed. An earlier study conducted in district Kangra in the year 1999 revealed a goiter prevalence of 12.1%.[6] The increase in TGR from 12.1% in 1999 to about 20% in 2004 could be possibly due to consumption of iodized salt with less than 15 ppm of iodine by a higher percentage of population. Similar results were obtained in an earlier study.[6]
Discussion
Urine samples were collected from 685 children included in the study. The proportion of children with UIE levels <20.0, 20.0- 49.9, 50.0-99.9 and = 100 μg/l was 0.3, 1.3, 8.3 and 90.1%, respectively. Only 1.6% of the samples had UIE level less than 50.0 μg/l [Table - 2]. The median UIE levels of the study subjects was found to be 200 μg/l indicating that there was no biochemical deficiency of iodine in the subjects studied. Earlier studies conducted in district Kangra in 1995 and 1999 also showed median UIE levels of 165 μg/l and 150 μg/l, respectively.[6],[12]
The salt samples were analysed using the spot testing kit method. It was observed that out of a total of 534 salt samples collected, 2.4%, 33.6% and 64% of salt samples has nil, less than 15 ppm and 15 ppm and more of iodine, respectively.
In the present study, higher percentage of families (36%) were consuming salt with iodine content of less than 15 ppm which was below the stipulated level of iodine. Earlier studies in district Kangra in 1995 and 1999 reported that 23% and 12.7% of the families were consuming salt with less than 15 ppm of iodine, respectively.[6],[12] The higher percentage of families consuming salt with less than 15 ppm of iodine may be possibly due to lifting of central ban "on sale of non iodized salt" in 2000. Only 1.6% of children had UIE levels less than 50mcg/dl possibly because these children continue to receive some iodine from the diet and partly from the inadequately iodised salt they consumed.
The TGR represents the chronic iodine deficiency while the UIE levels indicate the current iodine nutriture. The findings of the present study revealed that the current iodine status of the population in district Kangra was adequate (as revealed by the median UIE levels of more than 100 μg/l ). However, the TGR of 19.8% showed existence of mild iodine deficiency. This could be possibly due to higher percentage of families consuming salt with less than 15 ppm of iodine. The persistence of goiter of more than 5% amongst school aged children indicate the need of continued monitoring the quality of iodised salt provided to the beneficiaries under the Universal salt iodisation programme in order to achieve the goal of IDD elimination from Kangra valley.
References
1.Ramalingaswami V, Subramanian TA, Deo MG. The aetiology of Himalayan endemic goiter. 1961. Natl Med J India 2001; 14: 180-184.
2.Agrawal DK, Agarwal KN. Current status of endemic goiter in some areas of sub-Himalayan belt. Indian Pediatr 1983; 20: 471-477.
3.Karmarkar MG, Ramalingaswami V. Pathophysiology of Himalayan endemic goiter. Acta Endocrinol 1973; 179: 38-39.
4.Sooch SS, Deo MG, Karmarkar MG, Kochupillai N, Ramachandran K, Ramalingaswami V. Prevention of endemic goiter with iodised salt. Bull WHO 1973; 49: 307-312. [PUBMED]
5.Sooch SS, Deo MG, Karmarkar MG, Kochupillai N, Ramachandran K, Ramalingaswami V. The Kangra valley experiment: prevention of Himalayan endemic goiter with iodinated salt. Acta Endocrinol 1973; 179: 110. [PUBMED]
6.Kapil U, Sohal KS, Sharma TD, Tandon M, Pathak P. Assessment of iodine deficiency disorders using the 30 cluster approach in District Kangra, Himachal Pradesh, India. J Tropical Pediatr 2000; 46: 264-266. [PUBMED] [FULLTEXT]
7.Indicators for assessing iodine deficiency disorders and their control through salt iodisation. WHO/UNICEF/IDD. World Health Organisation , Geneva; 1994.
8.NFHS (2000) India 1998-1999- National Family Health Survey-2 (NFHS-2)- Himachal Pradesh. Background characteristics of households, 2000: 24.
9.Blinkin NJ, Sullivan K, Staehling N, Nieburg P. Rapid nutrition surveys : how many clusters are enough Disasters 1992; 16: 97-103.
10.Dunn JT, Crutchfield HE, Gutekunst R, Dunn D. Methods for measuring iodine in urine. A joint publication of WHO/UNICEF/ICCIDD; 1993. p. 18-23.
11.Kapil U, Dwivedi SN, Seshadri S, Swami SS, Beena, Mathur BP, Sharma TD, Khanna K, Raghuvanshi RN, Tandon M, Pathak P, Pradhan R. Validation of spot testing kit in the assessment of iodine content of salt: a multi-centric study. Indian Pediatr 2000; 37: 182-6. [PUBMED]
12.Kapil U, Saxena N, Ramachandran S, Sharma TD, Nayar D. Status of iodine deficiency in selected blocks of Kangra district, Himachal Pradesh. Indian Pediatrics 1997; 34 : 338-340. [PUBMED](Kapil Umesh, Sharma TD, Singh Preeti)
2 Health and Family Welfare Training Center, Kangra, District Kangra, Himachal Pradesh, India
Thirty primary schools were selected in district Kangra utilizing the population proportionate to size cluster sampling methodology in the year 2004. A total of 6939 children were included in the study. The clinical examination of the thyroid of each child was conducted. On the spot casual urine sample and salt samples were collected from a 'sub set of' children included in the study. The Total goiter rate (TGR) was found to be 19.8%. The median Urinary iodine excretion level was 200 μg/l and only 64% of the salt samples had the stipulated level of iodine. The findings of the present study revealed that current iodine status of population is adequate, however, TGR showed mild iodine deficiency (chronic), and there is a need of continued monitoring the quality of iodised salt provided to the beneficiaries under the Universal salt iodisation programme in order to achieve the goal of elimination of Iodine deficiency disorders from district Kangra.
Keywords: Goiter; Iodine deficiency disorders; Salt iodisation; Urinary iodine excretion
District Kangra in Himachal Pradesh, India is a known iodine deficiency endemic area.[1],[2],[3] A survey conducted in 1956 reported a goiter prevalence of 55% in the district.[4],[5] Subsequently, an intervention trial was conducted during 1955 to 1961 in the district Kangra resulted in reduction of goiter prevalence in the range of 20-30%. In 1973, a repeat survey was conducted and it was found that the continued salt iodisation programme further reduced the TGR to 8.5-9.1% in the district Kangra.[4] In 1999, another repeat survey was conducted. It was revealed that the prevalence of goiter as 12.1%.[6] Authors conducted a study during year 2004 with the objectives to assess the prevalence of IDD after 40 years of supply of iodised salt in the district Kangra and to estimate the iodine content of salt consumed by the population so that the state government can strengthen the existing Universal salt iodisation programme activities in the district, if required.
Materials and Methods
A school based study was conducted during January to March 2004 in district Kangra. The children in the age group of 8-10 years were included. The 30 cluster sampling methodology as recommended by the WHO/UNICEF/ICCIDD, was utilized for selecting the clusters. Keeping in view, the anticipated prevalence of iodine deficiency as 15%, a confidence interval of 95%, relative precision of 10% and a design effect of 3, a total sample size of 6531 was calculated.[7] In each cluster, 227 children in the age group of 8 to 10 years were included in the study. A total of 6939 children were included in the study.
The school enrollment rate of children in the age group of 8-10 years was more than 90% in district and hence, the school based approach was adopted.[8] All the primary schools in the district with their total enrollment were enlisted and thirty schools were selected for the detailed study utilizing the population proportionate to size cluster sampling methodology.[9] The identified schools were visited and the subjects were briefed about the objectives of the study during the school assembly. The clinical examination of the thyroid of each child was conducted. The goiter was graded according to the criteria recommended by the joint WHO/UNICEF/ICCIDD. When in doubt, the investigators recorded the immediate lower grade. The intra and inter observer variation was controlled by repeated training and random examinations of goiter grades by first author. The results were recorded in a pre-designed questionnaire. The sum of grades 1 and 2 provided the TGR of the study population.[7] If the requisite number of children could not be completed from the selected cluster/school, then the nearest adjoining school was included to complete the total number subjects to be covered in the cluster.
The study was linked with annual school health examination survey which was conducted in school routinely for which the informed consent was obtained.
On the spot casual urine sample were collected from every 10th child included in the study. Plastic bottles with screw caps were provided to children for the urine samples. The samples were stored in the refrigerator until analysis. The UIE levels were analysed using the wet digestion method.[10] A pooled urine sample was prepared for Internal Quality Control (IQC) assessment. The IQC sample was analysed 25 times with standards and blank in duplicate. This IQC sample having a known concentration range of iodine content was run with every batch of test samples. If the results of the IQC sample was within the range (ie. Mean ± 2SD) then the test was deemed in control and if the results were outside the range, then the whole batch was repeated. Salt was collected from every 13th child included in the study. The children were provided with auto seal polythene pouches with an identification slip. They were requested to bring four tea spoons of salt (about 20 g) from their family kitchen and the iodine content of salt samples was analysed by spot testing kit method.[11] The salt and urine samples were analysed by a trained technician.
Constraints of the Study
The intra and inter observer variation in goiter examination was controlled by repeated training and random examination of goiter grade by expert. However, inspite of all the precautions for the quality control, a possibility existed for misclassification of goiter grade I.
The non response rate was less than 1% as it was part of annual health examination and no intervention was conducted.
Results
A total of 6939 children in the age group of 8-10 years were included in the present study. Nearly 52.2% of the children were males and 47.8% were females. The age wise distribution of children according to the various grades of goiter is depicted in [Table - 1]. The total goiter prevalence was found to be 20.3% in boys and 19.2% in girls. It was observed that the total goiter rate increased with the increase in age. The TGR was found to be 19.8% (CI 21.78-17.82) in the present study. It has been documented that if more than 5% of the school aged children are suffering from goiter, the area should be classified as endemic to iodine deficiency.[7] The findings of the present study revealed that in district Kangra, mild iodine deficiency existed. An earlier study conducted in district Kangra in the year 1999 revealed a goiter prevalence of 12.1%.[6] The increase in TGR from 12.1% in 1999 to about 20% in 2004 could be possibly due to consumption of iodized salt with less than 15 ppm of iodine by a higher percentage of population. Similar results were obtained in an earlier study.[6]
Discussion
Urine samples were collected from 685 children included in the study. The proportion of children with UIE levels <20.0, 20.0- 49.9, 50.0-99.9 and = 100 μg/l was 0.3, 1.3, 8.3 and 90.1%, respectively. Only 1.6% of the samples had UIE level less than 50.0 μg/l [Table - 2]. The median UIE levels of the study subjects was found to be 200 μg/l indicating that there was no biochemical deficiency of iodine in the subjects studied. Earlier studies conducted in district Kangra in 1995 and 1999 also showed median UIE levels of 165 μg/l and 150 μg/l, respectively.[6],[12]
The salt samples were analysed using the spot testing kit method. It was observed that out of a total of 534 salt samples collected, 2.4%, 33.6% and 64% of salt samples has nil, less than 15 ppm and 15 ppm and more of iodine, respectively.
In the present study, higher percentage of families (36%) were consuming salt with iodine content of less than 15 ppm which was below the stipulated level of iodine. Earlier studies in district Kangra in 1995 and 1999 reported that 23% and 12.7% of the families were consuming salt with less than 15 ppm of iodine, respectively.[6],[12] The higher percentage of families consuming salt with less than 15 ppm of iodine may be possibly due to lifting of central ban "on sale of non iodized salt" in 2000. Only 1.6% of children had UIE levels less than 50mcg/dl possibly because these children continue to receive some iodine from the diet and partly from the inadequately iodised salt they consumed.
The TGR represents the chronic iodine deficiency while the UIE levels indicate the current iodine nutriture. The findings of the present study revealed that the current iodine status of the population in district Kangra was adequate (as revealed by the median UIE levels of more than 100 μg/l ). However, the TGR of 19.8% showed existence of mild iodine deficiency. This could be possibly due to higher percentage of families consuming salt with less than 15 ppm of iodine. The persistence of goiter of more than 5% amongst school aged children indicate the need of continued monitoring the quality of iodised salt provided to the beneficiaries under the Universal salt iodisation programme in order to achieve the goal of IDD elimination from Kangra valley.
References
1.Ramalingaswami V, Subramanian TA, Deo MG. The aetiology of Himalayan endemic goiter. 1961. Natl Med J India 2001; 14: 180-184.
2.Agrawal DK, Agarwal KN. Current status of endemic goiter in some areas of sub-Himalayan belt. Indian Pediatr 1983; 20: 471-477.
3.Karmarkar MG, Ramalingaswami V. Pathophysiology of Himalayan endemic goiter. Acta Endocrinol 1973; 179: 38-39.
4.Sooch SS, Deo MG, Karmarkar MG, Kochupillai N, Ramachandran K, Ramalingaswami V. Prevention of endemic goiter with iodised salt. Bull WHO 1973; 49: 307-312. [PUBMED]
5.Sooch SS, Deo MG, Karmarkar MG, Kochupillai N, Ramachandran K, Ramalingaswami V. The Kangra valley experiment: prevention of Himalayan endemic goiter with iodinated salt. Acta Endocrinol 1973; 179: 110. [PUBMED]
6.Kapil U, Sohal KS, Sharma TD, Tandon M, Pathak P. Assessment of iodine deficiency disorders using the 30 cluster approach in District Kangra, Himachal Pradesh, India. J Tropical Pediatr 2000; 46: 264-266. [PUBMED] [FULLTEXT]
7.Indicators for assessing iodine deficiency disorders and their control through salt iodisation. WHO/UNICEF/IDD. World Health Organisation , Geneva; 1994.
8.NFHS (2000) India 1998-1999- National Family Health Survey-2 (NFHS-2)- Himachal Pradesh. Background characteristics of households, 2000: 24.
9.Blinkin NJ, Sullivan K, Staehling N, Nieburg P. Rapid nutrition surveys : how many clusters are enough Disasters 1992; 16: 97-103.
10.Dunn JT, Crutchfield HE, Gutekunst R, Dunn D. Methods for measuring iodine in urine. A joint publication of WHO/UNICEF/ICCIDD; 1993. p. 18-23.
11.Kapil U, Dwivedi SN, Seshadri S, Swami SS, Beena, Mathur BP, Sharma TD, Khanna K, Raghuvanshi RN, Tandon M, Pathak P, Pradhan R. Validation of spot testing kit in the assessment of iodine content of salt: a multi-centric study. Indian Pediatr 2000; 37: 182-6. [PUBMED]
12.Kapil U, Saxena N, Ramachandran S, Sharma TD, Nayar D. Status of iodine deficiency in selected blocks of Kangra district, Himachal Pradesh. Indian Pediatrics 1997; 34 : 338-340. [PUBMED](Kapil Umesh, Sharma TD, Singh Preeti)