A Cross-sectional study assessing the Prevalence ofIodine Deficiency Disorders among school children aged6 to 12 years in Tumakuru district of Karnataka

Introduction

Iodine is a micronutrient and normally required around 100-150 microgram/day for the synthesis of the thyroid hormones- thyroxine (T4) and triiodothyronine (T3) and essential for the normal growth and development as well as for the wellbeing of all the human beings. Deficiency of iodine can cause physical and mental retardation, cretinism, abortions, stillbirth, deaf-mutism, squint & various types of goitre¹. More than 1.5 billion population of the world are at the risk of Iodine Deficiency Disorders (IDD) out of which, it is estimated about 200 million people are in our country. The surveys conducted by the Central and State Health Directorates, ICMR and Medical Institutes have clearly demonstrated that not even a single State/UT is free from the problem of Iodine Deficiency Disorders².

In 1962 the Government of India launched a 100 percent centrally assisted National Goitre Control Programme (NGCP), which was renamed as National Iodine Deficiency Disorders Control Programme (NIDDCP) with a view of covering wide spectrum of Iodine Deficiency Disorders. Goals of NIDDCP are to bring the prevalence of IDD to <5% in the country and to ensure 100% consumption of adequately iodinated salt (15ppm) at the household level.To ensure the use of iodized salt, the Government of India has issued the notification banning the sale of non-iodinated salt for direct human consumption in the country with effect from May 2006 under the Prevention of Food Adulteration Act 1954². Findings of National family health survey-4 (NFHS,2015-16) shows that 93% of households are using iodized salt as compared to 73% in NFHS-3(2005-06)³

One of the objectives of NIDDCP is to conduct surveys to assess iodine deficiency disorders and the impact of iodized salt after every 5 years in the districts.¹ As a part of IDD survey being conducted in various districts of Karnataka, IDD survey was conducted in Tumakuru District during February March 2019 by Bangalore Medical College and Research Institute, Bengaluru under the guidance of Deputy Director (Nutrition), IDD cell,Directorate of Health and Family Welfare services. This study was conducted to study the prevalence of Goitre in children aged 6-12 years, to analyse the salt iodine level at consumer level and to determine the median Urinary Iodine Excretion among these children.

Materials and methods

Tumakuru District is the second largest district in the state of Karnataka with ten talukas namely- Tumakuru, Sira, Gubbi, Tiptur, Turuvekere, Kunigal, Madhugiri, Pavagada, Koratagere, Chikkanayakanahalli.

As per the District IDD Survey Guidelines provided, a cross sectional survey was conducted in 30 villages/wards of Tumakuru district during the time period of February-March 2019. All the doctors and field investigators were trained rigorously before the commencement of survey regarding clinical examination of goitre, salt and urine sample collection and transport. Initially, list of all the primary schools (government, private, aided) in Tumakuru district was collected from the DDPI of Tumakuru District. From the list, 30 primary schools were selected by Disproportionate Stratified random sampling with taluka as the stratifying unit. Necessary precautions were taken to avoid selection of 2 schools from the same village/ward. Consent was obtained from the school authorities to conduct the survey.

School authorities were informed to request all the children aged 6-12 years to bring salt samples from their residence (3-4 teaspoon of salt in a plastic zip cover) on the day of survey.

On the day of survey, children aged 6-12 years were selected by disproportionate stratified random sampling (class studying as the stratum) for clinical examination of goitre by doctors. By clinical examination, children were classified into different grades of goitre as explained in the table-2. Salt samples (for laboratory Iodine level estimation) and urine samples [3-5ml for estimation of Urinary iodine excretion] were collected by proportionate systematic random sampling from children. After the survey, a health awareness session on IDD was given by a doctor to all the children .The salt samples collected were transferred into independent Ziplock covers to avoid moistening of salt. Household salt samples were analysed for its iodine content using standard iodometric titration method.

The urine samples collected were transported in cold temperature conditions and were stored in refrigerator until they were analysed (within 24hrs of collection). Assessment of urinary iodine was done by an assay based on the Sandell-Kolthoff reaction. Based on the estimated levels of Urinary iodine excretion, children were classified into 4 groups as described in table number 3.

Results

Demographic details:

2875 children aged 6-12 years were examined for thyroid enlargement and other suggestive features of Hypo/Hyperthyroidism from 30 schools across all talukas of Tumakuru district. Mean+ SD age of the participants was 9.19±1.99 years. 1492(51.9%) were male and 1383 (48.1%) were female participants.

Prevalence of goitre:

The overall prevalence of goitre was 8.2% of which 8% was Grade 1 and 0.2% was Grade 2 Goitre. Females (9.3%) had marginally higher prevalence of goitre than males (7.2%). In addition to this, 165(5.7%) of the participants also had other clinical features suggestive of Iodine deficiency namely- pallor, facial puffiness, short stature, dry skin, and sparse hair.

Urinary Iodine excretion estimation:

A total of 270 urine samples were collected and analyzed for urinary iodine excretion (UIE). Range of UIE was 23-220 µg/L. Median UIE was found to be 104 µg/L implying IDD to be a severe public health problem in Tumakuru district. 155(57%) of the study participants had normal UIE (>100 µg/L). Mild (50-99µg/L) and moderate (20- 49µg/L) iodine deficiency was seen in 94(35%) and 21(8%) of study participants respectively.

Household salt samples Iodine estimation:

Analysis of iodine levels in 540 household salt samples showed that all the samples were adequately iodized with iodine content of >15 ppm. Iodine concentration in salt samples was in the range of 35.66 to 463.658 ppm with a median concentration of 160.47 ppm

Discussion

In this study, the goiter prevalence rate of 8.2% among 6–12-year school children indicated that IDD is a mild public health problem in Tumakuru district and 8% of the children had grade 1 and 0.2% had grade 2 goitre.

Similarly, findings were observed in a study done in 2015 by Biradar et al in Ramanagar district goiterprevalence rate was 8.6%.⁴ And in Shimoga district survey in 2014 by Praveen et al, goiter prevalence was found to be 9.3%.⁵

In contrast, a survey done by Sonavane R.S et al conducted in Gadag district in 2016 showed that the prevalence rate among 6–12-year children was 22.78%. Among this, 19.67% of children had grade 1 and 3.11% had grade 2 goitre, indicating that IDD is a severe public health problem in this district.⁶ In a survey at Bharuch district of Gujarat in 2012 by Chandwani H.R et al goitre prevalence was found to be 23.2% (grade 1 – 17.4%, grade 2 – 5.8%)⁷

In this study, females (9.3%) had marginally higher prevalence of goitre than males (7.2%). In a survey done in 2005 at Belgaum district, prevalence of palpable and visible goitre was significantly high among females (21.8%) when compared to that of males (7.2%).⁸ And in survey done in Ramanagar district in 2015, females had higher prevalence compared to males in all the age groups but the difference was not statistically significant (0.437)⁴

In the present study, iodine concentrations in 540 salt samples were tested. Out of these was iodine concentration in 540(100%) household salt samples collected was >15 ppm, indicating all the salt samples to be adequately iodized. In contrast to this, study conducted in Gadag district showed that 39.63% of the salt samples had iodine concentration less than 15 ppm of which 15.93% had no iodine content in them showing that salt was iodized inadequately at the manufacturer level or due to loss of iodine during distribution process.⁶ And in a survey done in 2015 in Ramanagar district 95.3% had iodine concentration ≥ 15 ppm at the household level.⁴ In this study, 57% of the study participants from whom urine sample was collected had normal UIE (UIE>100 µg/L), 35% had moderate iodine deficiency and 8% had mild iodine deficiency. Median UIE concentration was found to be 104 µg/L (Range 23 to 220 µg/L) which implies IDD is not a public health problem in Tumakuru.

In contrast, in a study done at Gadag district, out of the 270 urine samples, it was found that 39.36% had moderate iodine deficiency and 38.88% had mild iodine deficiency. A study done in Himachal Pradesh in 2000 by Kapil et al, 3.5%,3.8%, 142% had urinary iodine excretion of <20, 20-49.9, 50-99.9 µg/L.⁹

Conclusion

Considering prevalence of goitre in 6-12 years children, Tumakuru district is ‘Endemic’ for Iodine deficiency disorder. But as inferred from median UIE obtained, IDD is not a public health problem of significance. These contradictory findings may be due to subclinical hypothyroidism cases which will show up only in UIE tests as they will not have goitre on neck examination. Household level salt is adequately iodized as per NIDDCP recommendations

Recommendations

Continue compulsory iodization of all common salt. Intensified Information, Health education and communication activities to school children, teachers and general public regarding consumption of iodized salt and broad spectral health problems of iodine deficiency. Regular monitoring of the quality of iodized salt.

Limitations

Even if intensified training was given to doctors on clinical examination for goitre, to some extent subjective bias do exists. Because of longer travel duration between field and laboratory, urine samples could not be analysed within 2 hours of collection