Excess iodine intake and its relation with thyroid dysfunction

 

For the control of Iodine Deficiency Disorder (IDD), Universal salt Iodization (USI) was implemented. As a result of it, Nepal is heading towards iodine sufficiency however the prevalence of clinical and sub-clinical hypothyroidism is still higher.The increased prevalence of thyroid disorders can be result of iodine deficiency or excess of iodine intake. The prevalence of excess iodine intake is hiking all over the world including Nepal. A study done in 1000 patients (with 270 clinical hypothyroidism patients) showed anti-TPO (Thyroid Peroxidase) antibody positive. The study also stated that the cause of hypothyroidism in present day Nepal was chronic autoimmune thyroiditis (Hashimoto's thyroiditis). As stated earlier, the status of iodine consumption in Nepal is moving from iodine deficiency to adequate or excess, there might be higher burden of thyroid disorders in Nepal due to the increased prevalence of autoimmune thyroiditis (Pokharel, S., 2019). 

A community based cross sectional study done in Udaypur (Nepal) in primary school aged children (6 years to 12 years) showed 10% (n=20) prevalence of thyroid dysfunction (sub-clinical hypothyroidism). Majority of the participants were reported to have excess urinary iodine concentration (UIC). The sensitive marker of recent dietary iodine intake is Urinary iodine rather than thyroid dysfunction. The analysis of thyroid hormones showed 1.6% of school age children had sub-clinical hyperthyroidism.

Although any apparent clinical consequences are not resulted by excess iodine exposure, thyroid dysfunction can occur in sensitive patients with specific risk factors, including those with pre-existing thyroid disease, the elderly, fetuses and neonates. The iodine-induced hypothyroidism or hyperthyroidism could be either sub-clinical or overt, hence excess iodine exposure should be suspected. The aeitology of thyroid dysfunction in not discernible.

Besides, Iodine Global Network (IGN) has highlighted several countries around the world to be categorized as having excess iodine status in population. As per study done in school age children in 6-9 years of age, IGN has listed Nepal in excessive iodine intake country. So, this could necessitate for the revisit of iodine standard in Nepal.

References

Thyroid dysfunction in region of excess iodine intake of Eastern Nepal, Saroj Thapa, Madhab Lamsal, Rajendra K. Chaudhari, Basanta Gelal, Saroj Kunwar, Nirmal Baral

DOI: http://dx.doi.org/10.18203/issn.2454-2156.IntJSciRep20181848

Iodine Global Network. Global score card of Iodine Nutrition in 2017 in the general population and in pregnant women (PW). IGN, Zurich, Switzerland. 2017. https://www.ign.org/scorecard.htm. Accessed on 29 july 2020.

Tamang, M.K., Gelal, B., Tamang, B. et al. Excess urinary iodine concentration and thyroid dysfunction among school age children of eastern Nepal: a matter of concern. BMC Res Notes 12, 294 (2019). https://doi.org/10.1186/s13104-019-4332-y

Pokharel, S. (2019). Cause of Hypothyroidism in Post Universal Salt Iodization era in Nepal. Journal of Diabetes and Endocrinology Association of Nepal, 3(1), 10-15. https://doi.org/10.3126/jdean.v3i1.24059

Leung, A.M. & Braverman, L.E. (2013). Consequences of excess iodine. Nature Reviews Endochrinology, 10(3), 136-142.