This was a community based cross-sectional study conducted in school children during September 2014 to August 2015 in Udayapur district of eastern Nepal. The study was conducted by the department of biochemistry in collaboration with department of pediatrics of B. P. Koirala Institute of Health Sciences (BPKIHS), Dharan, Nepal. A multistage random sampling technique was used to enroll school children aged 6 to 14 years in the study. Total of 1012 children from 4 VDCs (Beltar, Basaha, Rampur and Chaudandi) of Udayapur district participated in the study. In the first stage, urine samples were collected from all participants and based on the UIC data, 83 blood samples out of 112 children who had UIC < 100 µg/L were collected to assess thyroid function and thyroglobulin level. The study was approved by Institutional Ethical Review Committee (IRC) of BPKIHS (Code No: IRC/422/014, Date-16/02/2015) and was conducted in accordance to Helsinki declaration of 1975.
A written informed consent was obtained from the guardian of children prior to participation in study. All the stake holders including participants were informed about the purpose of the study. All healthy school going children (aged 6–14 years of age) were included in the study. Children taking drugs that interfere in thyroid function, taking iodine supplement or with any severe illness were excluded. Anthropometric measurements (height and weight) were taken, and spot urine samples were collected from all participants. Urine samples were collected in a clean, tightly screw-capped plastic vial and transported to the biochemistry laboratory for analysis. Blood samples (3 ml) were collected in plain vial by venipuncture following the standard protocol. Clotted blood was centrifuged at 3000 rpm and serum was separated. Serum and urine samples were refrigerated at -20 ºC until analysis. Urinary iodine concentration was estimated by ammonium persulfate digestion microplate (APDM) method using Sandell-Kolthoff’s reaction [10]. Serum free tri-iodothyronine (T3), free tetra-iodothyronine (T4), TSH and thyroglobulin (Tg) were measured by ELISA using commercial kits (Diametra Company).
The data was analyzed using SPSS version 20.0. The data are presented in form of mean ± SD, median with inter quartiles (IQR) and frequency (percentage). Chi-square test was applied to see statistical difference. Spearman’s and Pearson’s correlation analysis was used to find relationship between quantitative variables. P value of ≤ 0.05 was considered statistically significant at 95% confidence interval.
Total of 1012 school children (482 males and 530 females) from 4 VDC of Udayapur district participated in the study. The average ± SD age, weight and height were 10.94 ± 2.32 years versus 10.7 ± 2.31 years, 28.5 ± 7.82 kg versus 29.53 ± 9.56 kg and 131.82 ± 14.04 cm versus 131.48 ± 14.80 cm in males and females respectively. The median UIC with IQR was 236.0 µg/L (156.0, 331.38) indicating adequate iodine intake. The median UIC (IQR) among male and female children were 219 µg/L (149, 335) and 248 µg/L (165, 330) respectively. The UIC had significant positive correlation with the height (r = 0.098, p = 0.002) and weight (r = 0.0.112, p < 0.001) of the children.
Table 1 shows the classification of iodine nutrition status in the study participants according to modified WHO assessment criteria with adequate and more than adequate group merged as sufficient category [3]. The overall prevalence of iodine deficiency based on individual UIC cutoffs in our study was 11.1% (i.e severe, moderate and mild deficiency).
Table 1
Iodine status according to gender
| | Severe ID (< 20 µg/L) | Moderate ID (20–49 µg/L) | Mild ID (50–99 µg/L) | Sufficient (100–299 µg/L) | Excessive (> 300 µg/L) | P value |
Gender | Male (n = 482) | 5 (0.5%) | 13 (1.2%) | 40 (3.9%) | 266 (26.3%) | 158 (15.6%) | 0.5 |
Female (n = 530) | 4 (0.4%) | 19 (1.8%) | 31 (3.0%) | 291 (28.7%) | 185 (18.3%) |
| Total (n = 1012) | 9 (0.9%) | 32 (3.2%) | 71 (7.0%) | 557 (55.0%) | 343 (33.9%) | |
ID = Iodine deficiency |
The data is expressed as frequency (percentage). Chi-square test was used between gender and iodine status at 95% confidence interval. |
The mean fT3, fT4, TSH and median Tg (IQR) in children with insufficient UIC were 2.55 ± 0.43 pg/mL, 0.96 ± 0.28 ng/dL, 3.60 ± 1.44 mIU/L, and 17.5 (12, 29.4) ng/mL respectively. Out of 83 participants with low UIC, 75 had normal thyroid function, 5 had overt hypothyroidism and 3 had subclinical hypothyroidism as shown in Table 2. Tg has positive correlation with fT3 (r = 0.273, p = 0.013) as shown in Fig. 1.
Table 2
Thyroid function in children with insufficient UIC
| | Normal | Overt hypothyroidism | Subclinical hypothyroidism | P value |
Gender | Males (n = 40) | 36 (43.4%) | 2 (2.4%) | 2 (2.4%) | 0.761 |
Females (n = 43) | 39 (46.9%) | 3 (3.6%) | 1 (1.2%) |
| Total (n = 83) | 75 (90.3%) | 5 (6.0%) | 3 (3.6%) | |
UIC = Urinary iodine concentration |
The data is expressed as frequency (percentage). Chi-square test was used between gender and thyroid function status at 95% confidence interval. |
Iodine deficiency has remained as the most common cause of preventable brain damage in children worldwide [11]. Supplementation of iodine in salt through universal salt iodization has become effective in Nepal as shown by improving median UIC in the previous studies from eastern Nepal [6–8]. Median UIC indicates recent iodine intake and is used as marker of iodine status in the community settings. In the present study, median UIC was 236.0 µg/L which indicates sufficient iodine nutrition among children of this district. Previous report showed median UIC of 268.02 µg/L among children of this district [7].
In this study 11.1% children had UIC < 100 µg/L which is considered as iodine deficiency. In the previous study, iodine deficiency in this district was 12.7% [7]. National surveys conducted in Nepal in the year 1998, 2005 and 2007 depicted iodine deficiency in 43.6%, 27.4% and 19.4% school age children respectively [12]. In another study in eastern regions, Dhankuta and Dharan, iodine deficiency was 26.6% and 15.6% respectively among school children [13, 14]. Our findings suggest improvement in iodine nutrition in this region over previous years. This reveals the effectiveness of universal salt iodization program in Nepal. The fluctuation in diet across different seasons are also said to affect UIC of population leading to variation of UIC across various seasons in the same population [15].
Thyroglobulin, a thyroid-specific protein and precursor in the synthesis of thyroid hormones, is also considered as a sensitive marker of the iodine status than UIC [16]. The median thyroglobulin level in the children with insufficient UIC was 17.5 ng/mL. Our previous study among pregnant women of eastern Nepal reported median Tg of 6.5 ng/mL [17]. Thyroglobulin increment in plasma is also seen with thyroid mass, inflammation and hyperactivity of TSH [18].
We observed normal thyroid function in majority of children with iodine deficiency. Out of 83 children with insufficient UIC, 6% (n = 5) had overt hypothyroidism and 3.6% (n = 3) had subclinical hypothyroidism. Previous studies by Shakya et al., Chaudhari et al., and Khatiwada et al. found subclinical hypothyroidism in 19.5% and 16.7% (in Morang and Sunsari respectively), 31.8% and 25.59% (in Sunsari and Dhankuta respectively) and 17.6% respectively (in hilly regions) [19, 14, 20]. Thyroid dysfunction, specifically hypothyroidism was less common in this study than shown by our previous studies. This might be due to thyroid function assessment only in the subgroup with low UIC. In addition, there are other causative factors for thyroid disorders such as thyroid autoimmunity which might have been missed from this subgroup [17]. Thyroid function is said to be impaired in both the condition of iodine deficiency and excess [1].
We observed weak negative correlation of UIC with Tg level and thyroid hormones in children with insufficient UIC, and a positive correlation between thyroglobulin and fT3 (r = 0.273, p = 0.013). In iodine deficient cases, thyroglobulin tends to rise due to hyperactivity of thyroid gland and TSH however thyroid gland may be able to adapt to short term iodine deficiency maintaining normal thyroid hormones [1].
In summary, we found adequate iodine nutrition among the school children with small fraction having recent iodine deficiency, with the majority of children showing normal thyroid function.