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 Table of Contents  
Year : 2015  |  Volume : 2  |  Issue : 3  |  Page : 135-139

Urinary iodine levels, goiter rates and intelligence quotient in primary school children in Giwa Local Government area of Kaduna State, Nigeria

1 Department of Paediatrics, Ahmadu Bello University Teaching Hospital Shika, Zaria, Kaduna State, Nigeria
2 Department of Chemical Pathology, Ahmadu Bello University Teaching Hospital Shika, Zaria, Kaduna State, Nigeria

Date of Submission09-Nov-2014
Date of Decision11-Dec-2014
Date of Acceptance04-Mar-2015
Date of Web Publication6-Aug-2015

Correspondence Address:
Ogunrinde G Olufemi
Department of Paediatrics, Ahmadu Bello University Teaching Hospital Zaria
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/2347-9906.162325

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Background: Iodine deficiency can cause brain damage and/or cognitive impairment in children. It is preventable and of public health concern. After sixteen years of universal salt iodization in Nigeria, we undertook this study in north-western Nigeria to determine: prevalence of iodine deficiency in school children, any relationship between iodine deficiency, goiter and intelligence quotient and iodine content of table salt from their households. Methodology: A cross-sectional study of school children aged 6-12 years. Data was collected using structured questionnaire. Enrolled children had physical examination and anthropometric measurements. Presence of goiter was clinically assessed using criteria jointly recommended by WHO, UNICEF and ICCIDD. Intelligence quotient was assessed using the "Draw-A-Man" test. Specimen of urine was obtained from each child and table salt specimen from their homes. Atomic absorption spectrophotometry was used to analyze urinary iodine in μg/L. Iodine content of salt was semi-quantitatively analyzed. Results: A total of 544 children were studied. Their mean age (±1SD) was 9.5 ± 2.0 years. Median urinary iodine excretion (UIE) level was 148 μg/L. Forty-seven (8.6%) children had goiter. Three hundred and seventy- six (69.1%) children had normal body build. Of 118 (21.7%) children with adequate iodine status, 18 (15.3%) were stunted; a similar proportion in iodine deficient children. One hundred and thirty-four (57.0%) of 235 iodine-deficient children and 67 (56.8%) of 118 iodine-sufficient children had normal Intelligence Quotient. All household table salts contained iodine. Conclusion: There was no relationship between nutritional status and Iodine status; iodine status and intelligence quotient in study children.

Keywords: Goiter rates, intelligence quotient, Nigeria, primary school children, urinary iodine levels

How to cite this article:
Jane O A, Olufemi OG, Tajudeen R, Isah A, Rasheed Y. Urinary iodine levels, goiter rates and intelligence quotient in primary school children in Giwa Local Government area of Kaduna State, Nigeria. J Obes Metab Res 2015;2:135-9

How to cite this URL:
Jane O A, Olufemi OG, Tajudeen R, Isah A, Rasheed Y. Urinary iodine levels, goiter rates and intelligence quotient in primary school children in Giwa Local Government area of Kaduna State, Nigeria. J Obes Metab Res [serial online] 2015 [cited 2020 Feb 28];2:135-9. Available from: http://www.jomrjournal.org/text.asp?2015/2/3/135/162325

  Introduction Top

Iodine deficiency disorders (IDDs) continue to be a major public health problem. The socioeconomic development of affected populations is threatened globally despite the progress made on the deficiency control. [1],[2] It is the single most important preventable cause of brain damage. [2],[3] Iodine deficiency can result in brain damage and subtle cognitive impairment. HYPERLINK \l "3" [4] As a consequence, it has been linked with lowered intelligence quotient scores. [5] Sixteen years after universal salt iodisation in Nigeria, [6] we initiated this study in the north-western Nigeria to determine the prevalence of iodine deficiency in school children and to investigate any relationships between iodine deficiency, goiter and intelligence.

  Methodology Top

The objectives of the study were as follows:

  • To assess the nutritional iodine status of school children in Giwa Local Government Area (LGA) of Kaduna state, Nigeria
  • To correlate clinical nutritional status with iodine status
  • To investigate the relationship of the iodine status with intelligence quotient of these school children
  • To assess the consumption of iodised salt by these children.
This community-based cross-sectional study involved primary school children in the age bracket 6-12 years. Ethical clearance for the study was obtained from the Medical and Ethics Committee of Ahmadu Bello University Teaching Hospital, Zaria. The study was also approved by the Local Government Authority and the State Ministry of Education. The school authorities also gave an informed consent. Parental consent was taken. The children on thyroid replacement therapy, with mental retardation due to other causes (e.g. Down syndrome, birth asphyxia, kernicterus) and when parents did not give consent, were excluded from the study.

An interviewer-administered pre-tested structured questionnaire was used for data collection by two teams specifically trained for the study. A general physical examination was conducted on each enrolled child. The height and weight of the children were measured using standard techniques. The presence of goiter was assessed clinically by two members of each team and the findings reconciled before documentation. The grading of goiter was done according to the criteria jointly recommended by WHO, UNICEF, and ICCIDD. [7]

The intelligence quotient (IQ) of each child was assessed using the "Draw-A-Man" test. [8] Each child was given a sheet of paper and a pencil and requested to draw a man to the best of his/her ability. No further instruction was given and no time restriction was placed on the test. The drawings were, however, collected before the children left the study venue. The IQ was assessed using the Draw-A-Man test, which was discussed with a psychologist. This test is standardised with a simple and well described scoring scale. The test has qualitative features used to assess the maturation levels of children across ages 6-12 years. The qualitative scores are weighted quantitatively and divided by age in months to standardise it. It can be used alone to assess IQ in children.

Each child was supervised in the passage of a clean-catch mid-stream specimen of urine into a clean specimen bottle, and later given an auto-seal polythene pouch and instructed to put a teaspoonful of salt used in their homes into the bag, and bring to the same school the following morning.

All the urine specimens collected were refrigerated within an hour of collection and were treated as follows: 5 ml of urine specimen was added to 5 ml of perchloric acid and 5 ml of nitric acid and thoroughly mixed. The content of the test tube was heated until steaming at 110°C. After digestion, the content of the test tube was made up to 25 ml with deionised water. This procedure was done to remove interfering agents such as ascorbic acid, chlorine, colour, and proteins.

For iodine analysis, about 10 ml of the clear digested urine specimen was taken in a sample cell and the content of DPD total chlorine powder added and swirled to mix. The mixture was then left to stand for 3 min. Another sample cell was filled with 10 ml of digested urine sample (without DPD total chlorine powder) to serve as blank. The urine was analysed for iodine using atomic absorption spectrophotometry. [9] The Hach program in the atomic absorption spectrophotometer machine (Shimadzu A6800) was then selected and set at the element of interest wavelength at 530 nm. The absorbance values of the iodine in the sample were read after establishing zero absorption point. The concentration of iodine in each sample was measured on a qualitative scale as specified by kit and was read directly in μg/L.

  Results Top

A total of 544 children were studied. There were 287 boys and 257 girls, with no statistical difference in terms of their mean age, order of birth and family size between boys and girls. (Data not shown). [Table 1] shows the urinary iodine levels in boys and girls at each year of age from 6 to 12. The median urinary iodine level in this study is 148 μg/L. For boys, it is 130 μg/L and 170 μg/L for girls. Disaggregated by age, the boys tend to have a lower median urinary excretion than girls except at age of 11.
Table 1: Median urinary iodine excretion in Giwa school children disaggregated by age and sex

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Overall, only 21.8% of school children in the schools studied had urine iodine levels that can be categorised as adequate, about a third (35.1%) of them had levels in excess of what is recommended, and almost half (43.2%) had varying degrees of iodine deficiency as reflected by their urine levels. Of the school children in this study, 27.4% had moderate and severe iodine deficiencies with levels below 50 μg/L and 20 μg/L, respectively. The distribution of urinary iodine status is not significantly different between sexes [Table 2]. Iodine nutritional status as determined by urinary iodine levels is not significantly associated with age (χ2 = 5.75; df = 4; P = 0.2180), birth order (χ2 = 1.98; df = 4; P = 0.74), or family size (χ2 = 8.32; df = 4; P = 0.08). A total of 47 children had palpably or visibly enlarged thyroid gland, giving a total goiter rate (TGR) of 8.6%. Twenty-three (48.9%) females had thyroid gland enlargement, and there was no statistically significant difference in the proportions of boys and girls having goiter (χ2 = 0.06; df = 1; P = 0.928). Twenty (42.6%) children with thyroid enlargement had iodine deficiency as determined by their urine levels. This was not significantly different from the proportion in children with no thyroid gland enlargement [Table 3].
Table 2: Urinary iodine levels of school children disaggregated by sex

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Table 3: Iodine status in school children disaggregated by thyroid gland enlargement

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There was no statistically significant association between thyroid gland enlargement on one hand and age (χ2 = 11.33; df = 6; P = 0.079), birth order (χ2 = 2.26; df = 1; P = 0.133) or family size (χ2 = 0.16; df = 1; P = 0.691) on the other hand.

Using the body mass index-for-age z-scores (BAZ), 376 (69.1%), all the school children who were studied were of normal body build, 8 (1.5%) were overweight, 93 (17.1%) were thin, and 67 (12.3%) were remarkably thin. No child was obese. The small number of overweight children was combined for the convenience of analysis with children of normal body build. The distribution of BAZ across the different categories of iodine status did not differ significantly (χ2 = 5.74, df = 4, P = 0.22). Disaggregation by sex did not change this relationship between BAZ and iodine status [Table 4].

Of the 118 children (21.7%) with adequate iodine status, 18 (15.3%) were stunted. The proportion was similar to that in those who were iodine-deficient (42 [17.9%] of 235; χ2 = 0.38, P = 0.537). Disaggregation by sex did not alter this relationship [Table 5].
Table 4: Distribution of BAZ by iodine status disaggregated by sex

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Table 5: Relationship between iodine status and height-for-age by sex

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One hundred and thirty-four (57.0%) of 235 iodine-deficient children had IQ in the normal range. This was similar to the 67 (56.8%) of 118 iodine-sufficient children with IQ in the normal range (χ2 = 0.00, P = 0.966). When analysed by age, there was still no significant relationship between iodine status and IQ except in the children aged 11 years [Table 6]. Among the 11-year old children, there were significantly more children with iodine excess (18 of 28, 64.3%) than iodine-sufficiency (5 of 18, 27.8%) who had IQ in the normal range (χ2 = 4.47, P = 0.034).

All the salt samples submitted by the school children tested positive for iodine. Using the two shades of blue coloration of the rapid test kit, as instructed by the manufacturer, 530 (97.4%) salt samples had an adequate amount of iodine.
Table 6: Intelligence quotient distribution by iodine status disaggregated by age

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  Discussion Top

The mean urinary iodine excretion (UIE) in the subjects covered by this study is 148 μg/L and falls within the range prescribed for an iodine-sufficient population. Disaggregated by sex, all the boys and girls had median values in the normal range prescribed. However, boys in the early grades of primary school tended to have lower median values in the mildly insufficient range, compared with the girls except at age 11. The explanation for this is difficult, especially as we are unable to show any relationship between nutrition and iodine status. This is further compounded by the fact that both sexes were exposed to iodised salt on account of the 100% salt iodisation rate found in the study. Although it is important to note that the method employed for analysis of iodine concentration in table salt was qualitative creating variation in actual quantity of iodine. The metabolic needs at puberty/adolescence and dietary preferences or habit may be the reason for this difference in urinary iodine estimation between males and females at age of 11. Cooking practices and salt consumption pattern in each household would determine the actual iodised salt intake. An unacceptably high proportion (43.2%) of children in this study had varying degrees of iodine deficiency as determined from their UIE. This high rate of iodine deficiency was the same in both sexes and among family type. Birth order does not seem to influence the rate of iodine deficiency.

The prevalence of goiter, which did not differ with sex is 8.6%. This is similar to the finding in an Indian study [10] but less than that in other studies in India, South East Spain, China, Indonesia and Iran [11],[12],[13],[14],[15],[16] but more than those found in another part of India. [17] The joint WHO/UNICEF/ICCIDD recommendation that where more than 5% of school children aged 6-12 years suffer from goiter, the area/location should be classified as endemic for iodine deficiency. [7] That means that by TGR, Giwa LGA may be described as being endemic for iodine deficiency, but it is important to note that goiter indicates a chronic situation of iodine deficiency. [14] Goiter may not regress dramatically with correction of iodisation of salt as was reported in South African school children where mandatory iodisation of salt virtually eradicated iodine deficiency within 1-year but the goiter rate in these children did not decline. [18] This was evident as more than 50% of the children with goiter had normal and excess UIE levels, while only <΍ were urinary iodine deficient. The UIE levels used in this study were in ranges and not the recommended median levels. This is so because UIE levels in the general populations are usually normally distributed, therefore, medium values are more appropriate and should be used rather than the mean values. [7]

The WHO/UNICEF/ICCIDD recommends that a no iodine deficiency state in an area would be indicated in a population when median urinary Iodine concentration is 10 mcg/dl and when not more than 20% of the urine samples have median urinary Iodine concentration <5 mcg/dl. [7],[19] Even though the overall median urinary iodine concentration in this study is in the normal range, more than 20% of school children had UIE of <50 μg/L and would therefore suggest that IDD may still be a significant health issue in the study site.

Large family size is a contributory factor or feature of poor socio-economic status as seen by a majority of the children in our study. Poor nutritional status is a characteristic of poor socio-economic status. The body mass index (BMI) of children in this study showed that a third was thin while none was obese. The absence of a significant relationship between goiter and age, sex or family size probably suggests that their iodine intake was optimal and therefore met their dynamic growth and metabolic needs. Pardede et al. [5] Lucia et al. [14] found a significant relationship between stunting and UIE level. Their stunted children had low UIE values. Some authors [14],[16] reported an insignificant relationship between the height of children and iodine status, which shows that urinary iodine levels reflect the current situation of iodine status.

Similar proportion of study children with urinary iodine deficiency and sufficiency were observed to have intelligence quotient within the normal range, indicating no significant association between UIE and IQ. This association remained the same when related to age except among 11-year-old children where there were significantly more children with iodine excess than iodine-sufficiency having normal IQ. This finding may have be due to the fact that the UIE level besides being a reflection of recent ingestion of iodine may also not be a sensitive or specific parameter to be used in isolation to assess IQ. Irrespective of poor iodine nutritional status of a child with the consequent effect on psychomotor development, a recent alteration in the concentration of ingested iodine would be reflected in their UIE level. This differs with the significant finding in an Indonesia study where children with low UIE levels had low Intelligence quotient. [14] Fernandez et al. in their study using the Cattell's factor test to measure IQ reported that IQ was significantly higher in children with urinary Iodine levels above 100 μg/L. They also found that the risk of an IQ falling below the 25 th percentile, and even having an IQ of 70 or less was greater in children with urinary Iodine levels of <100 μg/L. This was significantly related to intake of non-iodised salt and drinking of dairy products less than once in a day. [12]

Our study showed that similar proportions of children with adequate iodine status, as well as those with iodine deficient status, were stunted. In Indonesia, the children who were stunted had low UIE levels and intelligence quotient, and their goiter rate was higher than those who were not stunted. [14] The prevalence of goiter in our study indicated that the area of study was endemic for IDD. There was no significant association between UIE levels and goiter in this study. This finding differs from the report of a study in Russia where a significant negative correlation was observed between the prevalence of goiter and the median level of UIE. [20] The reason for our finding may be related to the actual duration of time when consumption of iodised salt commenced which is beyond the scope of this study since it is not a direct impact study of effects of iodisation of salt.

The goal of universal salt iodisation was that more than 90% of households should use iodised table salt. [7],[13],[19] Over 95% of table salt samples collected from all households in this study had an adequate amount of iodine. This shows that the iodisation of salt in Nigeria is successful. It is noteworthy that the method used for determination of iodine content of the salt was mainly a qualitative analysis. The finding of excessive UIE levels among our subjects is an indication that the amount of iodine in the salt needs to be reassessed as this may currently be in excess of required iodine. In China, the initial iodine level was set at 50 ppm, but later reduced to 35 ± 15 ppm after national monitoring of urinary iodine concentration showed that the concentration of 50 ppm led to excessive intake of iodine among their populace. [13]

  Conclusion Top

Iodine deficiency disorder is a public health problem in Giwa LGA of Kaduna state of Nigeria. There was no relationship between nutritional status and Iodine status as well as iodine status and intelligence quotient in the school children studied. Households in Giwa LGA have access to iodised table salt.

  Limitation of study Top

Thyroid function test and antibody estimation study is not in the scope of this study and may follow in a comparative study among those who have goiter with varying urinary iodine levels and intelligence when research funds are obtained as this study is quite expensive.

  Acknowledgement Top

We will like to acknowledge Ahmadu Bello University Zaria for partial funding for this study.

  References Top

Word Health Organization. Iodine status worldwide. In: de Benoist B, Anderson M, Egli I, Takkouche B, Allen H, editors. WHO Global Database on Iodine Deficiency. Geneva: World Health Organization; 2004.  Back to cited text no. 1
Hetzel BS. Progress in the prevention and control of iodine-deficiency disorders. Lancet 1987;2:266.  Back to cited text no. 2
World Health Organization. Assessment of Iodine Deficiency Disorders and Monitoring Their Elimination: A Guide for Programme Managers. WHO press, WHO, 20 Appia Avenue, 1211 Geneva 27, Switzerland. World Health Organization; 2007.  Back to cited text no. 3
Zimmermann M, Jooste P, Pandav C. Iodine-deficiency disorders. Lancet 2008;372:1251-62.  Back to cited text no. 4
Tang Z, Liu W, Yin H, Wang P, Dong J, Wang Y, et al. Investigation of intelligence quotient and psychomotor development in school children in areas with different degrees of iodine deficiency. Asia Pac J Clin Nutr 2007;16:731-7.  Back to cited text no. 5
de Benoist B, McLean E, Andersson M, Rogers L. Iodine deficiency in 2007: Global progress since 2003. Food Nutr Bull 2008;29:195-202.  Back to cited text no. 6
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Harris DB. Children's Drawings as Measures of Intellectual Maturity. New York: Harcourt, Brace and World, Inc.; 1963.  Back to cited text no. 8
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Chandra AK, Tripathy S, Lahari D, Mukhopadhyay S. Iodine nutritional status of school children in a rural area of Howrah district in the Gangetic West Bengal. Indian J Physiol Pharmacol 2004;48:219-24.  Back to cited text no. 11
Fernandez PS, Torres-Barahona R, Muela-Martinez JA, Rojo-Martínez G, García-Fuentes E,×Garriga MJ, et al. Intelligence quotient and Iodine intake: A cross-sectional study in children. J Clin Endocrin Metab 2004;89:3851-7.  Back to cited text no. 12
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Mousavi SM, Tavakoli N, Mardan F. Risk factors for goiter in primary school girls in Qom city of Iran. Eur J Clin Nutr 2006;60:426-33.  Back to cited text no. 15
Das DK, Chakraborty I, Biswas AB, Saha I, Mazumder P, Saha S. Goitre prevalence, urinary iodine and salt iodisation level in a district of West Bengal, India. J Am Coll Nutr 2008;27:401-5.  Back to cited text no. 16
Bhasin SK, Kumar P, Dubey KK. Comparison of urinary iodine excretion and goiter survey to determine the prevalence of iodine deficiency. Indian Pediatr 2001;38:901-5.  Back to cited text no. 17
Jooste PL, Weight MJ, Lombard CJ. Short-term effectiveness of mandatory iodization of table salt, at an elevated iodine concentration, on the iodine and goiter status of schoolchildren with endemic goiter. Am J Clin Nutr 2000;71:75-80.  Back to cited text no. 18
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  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]


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