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LETTERS TO THE EDITOR
Year : 2018  |  Volume : 22  |  Issue : 2  |  Page : 295-296

Is iodine excess associated with increased incidence of hypothyroidism?


1 Department of Pediatrics, Sri Balaji Medical College, Chennai, Tamil Nadu, India
2 Department of Endocrinology, Diabetology and Bariatric Medicine, Narayana Health City, Bengaluru, Karnataka, India
3 Department of Endocrinology, Diabetes and Metabolism, Sri Ramachandra Medical College and Research Institute, Chennai, Tamil Nadu, India

Date of Web Publication14-May-2018

Correspondence Address:
Shriraam Mahadevan
Department of Endocrinology, Diabetes and Metabolism, Sri Ramachandra Medical College, Porur, Chennai, Tamil Nadu
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ijem.IJEM_605_17

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How to cite this article:
Kannan S, Prabhu SR, Mahadevan S. Is iodine excess associated with increased incidence of hypothyroidism?. Indian J Endocr Metab 2018;22:295-6

How to cite this URL:
Kannan S, Prabhu SR, Mahadevan S. Is iodine excess associated with increased incidence of hypothyroidism?. Indian J Endocr Metab [serial online] 2018 [cited 2018 May 20];22:295-6. Available from: http://www.ijem.in/text.asp?2018/22/2/295/232383



Sir,

We appreciate the article written by Shrestha et al. titled, “Iodine status among subclinical and overt hypothyroid parents by urinary iodine assay” in the last issue our journal.[1] They have recommended reappraisal of salt iodization campaign to monitor for iodine excess which could be related to hypofunctioning of thyroid gland. However, there are certain clarifications requested to the authors regarding their observations that fortified iodine levels in consumed salt may be a major causative factor for thyroid dysfunction. The role of excess iodine in inhibiting release of thyroid hormone needs to be addressed carefully. Especially, if excess iodine should cause thyroid dysfunction, the actual source of excess iodine among the study population needs to be well defined and it could be in food, water, and salt,[2] and dose–response relationships inclusive of borderline excess intake and susceptibility factors for subclinical hypothyroidism and related thyroid antibody status need to be discussed.

This study would have been more informative if goiter characteristics of the study population were also included. Implementation of universal salt iodization (USI) program has been successful in improving iodine deficiency status in many developing countries, and decreasing goiter rates after an increase in urinary iodine concentrations following USI programs have been reported recently in China and Uganda.[3] Recent publication documenting increasing goiter rates at 13.5% and only 18.2% of households using iodized salt in the state of Tamil Nadu as per the survey done by Pandav et al.[4] strongly support and justify increase in iodine ppm content of consumed salt by our vulnerable populations.

There are several publications demonstrating drinking water and food with high iodine content accounting for excess of iodine while iodized salt may be the least contributor as per reports. The role of goitrogens is crucial in that there is improper utilization of iodine by thyroid gland, and to overcome this, appropriate increases in salt iodization are necessary.

As per literature search by Leung and Braverman [5] at one end of spectrum, people without any evidence of thyroid disease almost always remain euthyroid even if they consumed excess iodine and there is an escape from acute inhibitory effects of excess intrathyroidal iodide on organification process and, subsequently, thyroid hormone synthesis and adaptation to Wolff–Chaikoff effect occurs. At the other end, although underlying mechanism of iodine-induced hypothyroidism is controversial, it could be attributed to failure to adapt to Wolff–Chaikoff effect most probably due to a damaged thyroid as a result of previous pathological insults.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
   References Top

1.
Shrestha U, Gautam N, Agrawal KK, Jha AC, Jayan A. Iodine status among subclinical and overt hypothyroid patients by urinary iodine assay: A Case-control study. Indian J Endocrinol Metab 2017;21:719-23.  Back to cited text no. 1
    
2.
Sohn SY, Choi JY, Jang HW, Kim HJ, Jin SM, Kim SW, et al. Association between excessive urinary iodine excretion and failure of radioactive iodine thyroid ablation in patients with papillary thyroid cancer. Thyroid 2013;23:741-7.  Back to cited text no. 2
    
3.
3. Katagiri R, Yuan X, Kobayashi S, Sasaki S. Effect of excess iodine intake on thyroid diseases in different populations: A systematic review and meta-analyses including observational studies. PLoS One 2017;12:e0173722.  Back to cited text no. 3
    
4.
Pandav CS, Krishnamurthy P, Sankar R, Yadav K, Palanivel C, Karmarkar MG, et al. Areview of tracking progress towards elimination of iodine deficiency disorders in Tamil Nadu, India. Indian J Public Health 2010;54:120-5.  Back to cited text no. 4
[PUBMED]  [Full text]  
5.
Leung AM, Braverman LE. Consequences of excess iodine. Nat Rev Endocrinol 2014;10:136-42.  Back to cited text no. 5
    




 

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