Iodine deficiency in populations exposed to radioactive iodine

Iodine deficiency at critical stages during pregnancy and early childhood results in impaired development of the brain and consequently impaired mental function. Correction of iodine deficiency is crucial in all areas where the iodine intake is not meeting the physiological requirements in order to reach optimal iodine nutrition.

While a variety of methods exists for the correction of iodine deficiency, in practice the most commonly applied is universal salt iodization- the addition of suitable amounts potassium iodate to all salt for human and lifestock consumption (WHO 2001). The principal indicator of impact is median urinary iodine concentration. The sustainable elimination of iodine deficiency requires that median urinary iodine levels in the targeted population is at least 100 µg/L (WHO 2001).

It is well established that exposure to ionizing radiation from external sources can result in the development of thyroid cancer (Becker DV et al., 1996, Mitchell P, 1999). Iodine nutritional status at the time of exposure to radioactive iodine strongly affects the thyroid radiation dose received by the thyroid gland at the time of exposure, thyroid volume as well as thyroid function after the exposure (Robbins J. 2001). Iodine deficiency late after exposure to radioiodine, and the resulting increase in TSH, may increase the risk of cancer by increasing the cell rate of cell division and enhancing cell growth, but there are no relevant data in humans and the supporting data in animals are of limited value (Robbins J. 2001).

Long-term iodine prophylaxis may thus reduce the risk of developing thyroid carcinoma once the thyroid has been acutely exposed to radiation. Assuming that a genetic thyroid leison has occurred after acute exposure to radiation, correcting iodine deficiency, will decrease the level of TSH stimulation on the damaged thyroid cells, thus decreasing the well known proliferative effects of long-term TSH stimultion (Pacini 1998).

The findings of dramatic increase of thyroid cancer in children living in the Chernobyl area led to several hypotheses, including the possible increased vulnerability of iodine deficient populations to the hazards of exposure to radioactiv iodine. Almost all of the territories contamined by radiation from Chernobyl in Belarus, Russia and Ukraine are goitre endemic areas.

A recent study in the Chernobyl area showed that the risk of thyroid cancer was significantly associated with increasing thyroid radiation dose, and was inversely associated with urinary iodine concentration (Shakhtarin et al. 2003). There was also a joint effect of radiation exposure and iodine deficiency (Shakhtarin et al. 2003). Although preliminary, these findings suggest that elimination of iodine deficiency in areas affected by Chernobyl may be important in reducing the effects of radiation exposure on the thyroid.

The Chernobyl nuclear disaster and concern about these risks, alerted the Russian Federation to iodine deficiency in the area and to investigate the nutritional status of the population (Jackson RJ, 2002). Iodine deficiency, although a less dramatic threat than the immediate challenges of the Chernobyl incident, has the potential for a long-term impact on the population if it remains unrecognized and unattended. Prevention of iodine deficiency through salt iodization is has therefore been started in the Russian Federation.

References:

Becker DV, Robbins J, Beebe GW, Bouville AC, Wachholz BW. Childhood thyroid cancer following the Chernobyl accident. Endocrinol Metab Clin North Am. 1996;25:197-211.

Robbins J, Dunn JT, Bouville A, Kravchenko VI, Lubin J, Petrenko S, Sullivan KM, VanMiddlesworth L, Wolff J. Iodine Nutrition and the Risk from Radioactive Iodine: A Workshop Report in the Chernobyl Long-Term Follow-Up Study. Thyroid Volume: 11 Number: 5 Page: 487 -- 491

http://miranda.ingentaselect.com/vl=17399966/cl=27/nw=1/rpsv/cw/mal/10507256/v11n5/s10/p487

Jackson RJ, DeLozier DM, Gerasimov G, Borisova O, Garbe PL, Goultchenko L, Shakarishvili G, Hollowell JG, Miller DT. Chernobyl and iodine deficiency in the Russian Federation: an environmental disaster leading to a public health opportunity. J Public Health Policy. 2002;23(4):453-70.

Mitchell P. Ukrainian thyroid-cancer rates greatly increased since Chernobyl. The Lancet. 1999;354(9172):51.

Pacini F, Vorontsove T, Schlumberger M, Ronga G. Iodine status and Post-Chernobyl thyroid cancer. In "Elimination of iodine deficiency disorders (IDD) in central and eastern Europe, the Commonwealth of Independent States, and the Baltic States". World Health Organization, Regional Office for Europe, 1998 (Document WHO/EURO/NUT/98.1).

Shakhtarin VV, Tsyb AF, Stepanenko VF, Orlov MY, Kopecky KJ, Davis S. Iodine deficiency, radiation dose, and the risk of thyroid cancer among children and adolescents in the Bryansk region of Russia following the Chernobyl power station accident. Int J Epidemiol. 2003 Aug;32(4):584-91.

WHO. Assessment of Iodine Deficiency Disorders and Monitoring their Elimination. Geneva, World Health Organization, 2001 (Document WHO/NHD/01.1).

http://www.who.int/nut/documents/assessment_idd_monitoring_eliminination.pdf

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