Protecting the Thyroid in Times of Conflict (Ukraine 2022)

Introduction

With the onset of the war in Ukraine, radiation anxiety, evidenced by sales of potassium iodide (KI), began to surface widely, particularly after February 24th when the Reuters news organization reported “Chernobyl power plant captured by Russian forces” and subsequently on March 3rd with news of a fire in the Zaporizhzhia Nuclear Power Station, the largest in Europe (1 –3). Authoritative guidelines and reviews about using KI to protect the thyroid have been published and should be consulted for comprehensive coverage of the topic (4 –8). For the most part, these foresee a release of radioactive iodine from a power plant accident during peacetime. In this commentary, we summarize some basic facts about protecting the thyroid using KI, but we focus on the considerations arising in times of conflict.

What Role Does KI Play in Protecting the Thyroid?

KI reduces the exposure of the thyroid to radioactive iodine in two ways. First, it saturates the pathway by which iodine enters the thyroid. Second, it initiates the Wolff–Chaikoff effect by reducing the entry of radioactive iodine into the thyroid and reducing the residence time of any radioactive iodine that does enter the thyroid (9).

After the Chornobyl disaster, Poland demonstrated the feasibility and safety of making KI widely available (10). When KI is taken within a few hours of ¹³¹I ingestion it will block over 90% of radioiodine uptake, but it should only be taken when directed by local public health authorities based on the predicted radiation exposure. The radiation thresholds for KI prophylaxis along with the age-specific doses as recommended by the WHO are shown in Table 1. The risk of developing radiation-related cancer is much higher in children than in adults. In fact, the risk is so small in adults that it has been difficult to confirm a risk in people older than 15 years. Therefore, priority for using KI should decrease with advancing age corresponding to age-specific predicted thyroid exposure thresholds, with the youngest at greatest risk. KI is uncommonly contraindicated (8). People with goiters can take KI but are at risk of developing hyper- or hypothyroidism and should be followed appropriately.

KI protection lasts for about 24 hours. When evacuation is not possible and ¹³¹I exposure persists, current guidelines recommend daily KI administration (9); however, pregnant women and breastfeeding mothers require special consideration (8,11). Pregnant women should take one dose, but no more. Continued exposure of the fetus to high levels of iodine are deleterious. For breastfeeding mothers one dose followed by evacuation is preferred. If evacuation is not possible, the recommendations include additional doses administered to the mother and testing the child for hypothyroidism.

In the conflict zone itself, where radiation levels are likely to be the highest, numerous problems associated with instituting the aforementioned measures in times of conflict may arise (Table 2). Less obvious is the substantial difficulty of predicting potential radiation doses to the thyroid. This requires accurate information about how much radiation is released and up to the minute meteorological information about air flow patterns and the anticipated spread of radioactive material.

Beyond KI, What Are the Most Important Measures to Take to Protect the Thyroid?

Of highest importance for the thyroid is the avoidance of milk/dairy products from cows consuming radioactive iodine contaminated grass (the milk pathway), which was the primary source of radioactive iodine entering the thyroids of people exposed to fallout from the Chornobyl disaster (12). Evacuation to locations away from the source of radiation and, if not feasible, sheltering in place are also important.

What Issues Arise from Multinational Exposure to Radioactive Iodine?

Releases of radioactive iodine in the midst of a conflict are unlikely to be confined to a single country. The releases of radioactivity from the Chornobyl and Fukushima accidents demonstrated wide and international spread (13).

While the WHO and IAEA (International Atomic Energy Agency) provide some harmonization of guidelines across countries, this is not complete (14). In some countries the units used to express the threshold dose is mGy and in others mSv. In some countries the threshold is called “projected dose” and in others “avertable dose.” Most importantly, interventional dose levels vary from country to country.

What New Studies Have Been Reported Concerning KI Since the 2017 WHO Publication on the Topic?

The 2017 WHO report suggested four areas in need of additional research. The one most relevant to the current situation, and where additional data continue to emerge, was stated in that report in part as: “More data are needed on the dosage, optimal timing and regimens for multiple administrations of stable iodine in case of repeated or protracted releases of radioactive iodine and the adverse health effects of stable iodine administration.” New models to assess KI blocking efficacy incorporating the separate kinetics of the Wolff–Chaikoff effect have been developed and suggest that repeated KI administration is needed for prolonged radioiodine exposure, and that for longer exposure periods perchlorate, which is a competitive inhibitor of NIS, may be superior to KI given the waning of the Wolff–Chaikoff effect (15,16). However, perchlorate is not widely available. Whether or not multiple KI doses are safe remains uncertain based on a literature review by Benderitter et al. (17).

Because of the disruption of public health systems during a conflict, the possible need for multiple administrations is dramatically increased. Since the 2017 publication, new publications on this subject are available, virtually all employing model systems using KI administration to rats. At one end of the age spectrum, Lebsir et al. treated pregnant rats with KI daily for 8 days and then, studied the progeny 30 days after weaning (18). In addition to changes in thyrotropin (TSH) and free thyroxine (T4) levels, changes in the expression of specific genes in the cerebellum and cerebrum were found. Despite the possibility of overinterpreting studies in rodents, the conclusion is that multiple administration to pregnant women should be avoided.

At the other end of the age spectrum, Lebsir et al. studied multiple doses in adult rats (19). In brief, they found changes in gene expression in the thyroid, but not in circulating thyroid hormone levels. Again, extrapolating to humans, this might predict that administration of multiple KI doses could be safe in adults. In a similar adult rat model, Phan et al. found that thyroid uptake of radioactive iodine between daily doses of KI was reduced by 63–88% (20).

What Are the Most Important Facts to Convey to the Public and What Are the Impediments?

The Chornobyl disaster is so closely associated with thyroid cancer that convincing the public that some release of radioactive material may not be a risk to the thyroid would be difficult. Of course there are other risks associated with spent nuclear fuel stored, for example, at Chornobyl and other nuclear power station sites. Radioactivity spread from these sources could cause significant medical, psychological, and ecological effects.

The fire at the Zaporizhzhia Nuclear Power Station also is illustrative. Even if the reactors had been shut down in anticipation of an attack, it would take weeks for the radioactive iodine to decay to levels of no concern for having an impact on the thyroid glands of inhabitants (21). It took days for it to become clear that the fire was not in the plant itself. Early reports of increased radiation levels were eventually and authoritatively refuted by the IAEA. Ukraine is highly dependent on nuclear energy and its other nuclear power plants may become vulnerable to attack. As shown in Fukushima, even the loss of electricity to a power plant needed to cool the reactors can also lead to massive radioactive releases.

Of late the world has been reminded about the prevalence of misinformation during an emergency. With respect to misinformation related to radiation, the most egregious example to now is the Chornobyl disaster, when the extent of the radioactive releases was hidden for days (22). Evidence that this could happen again is foretold by an article in the Russian-sponsored RT news site published in 2013 with the title “Worse than Chernobyl: The inner threat of Fukushima” (23). Public officials and news outlets should rely on authoritative sources such as the IAEA.

Conclusions

In the event of a nuclear emergency, KI can offer temporary protection for persons evacuating to an area of safety. When evacuation is not possible as may be the case in times of conflict, the use of KI may give the public false reassurance while sheltering in place and avoiding the ingestion of contaminated food as KI only offers protection to the thyroid from radioiodine isotopes, and the safety and efficacy of multiple doses of KI has not been firmly established.

How can current planning be augmented, knowing that radioactive iodine may be released during wartime? There are several possibilities: (i) Beyond distributing KI around nuclear facilities, sufficient KI needs to be kept at the ready for emergency distribution according to predetermined policies. (ii) Plans should be made for the possibility that some parameters needed to determine predicted thyroid radiation doses may not be reliably available. (iii) Robust public health measures should be developed to promote the correct utilization of KI. International harmonization of guidelines would be helpful. (iv) Designating safe evacuation routes for civilians. (v) Health care workers need to be aware of the possible medical problems associated with KI, including the risk factors, diagnoses, and treatments involved. Of course it may not be possible to institute some or all of these practices within a war zone or in surrounding countries caring for a large influx of displaced persons.

Beyond the emergency response to a nuclear power plant accident, both the Chornobyl and Fukushima accidents have revealed limitations in the planning for the aftermath. A list of the areas that require attention include the following: (i) overdiagnosis, especially related to thyroid surveillance, (ii) ethical, including the relationship between delivering care and conducting research, and (iii) psychosocial and social factors, as carefully documented in people living in the area of the Fukushima accident (24 –26). In one recognition of these needs, the European Atomic Energy Community has supported an effort, the SHAMISEN project, to expand the scope of planning for them (27,28).

No matter what happens in Ukraine, with respect to the concerns about nuclear risks, the world will not return to status quo ante. Continued efforts to improve readiness, including protecting the thyroid gland, should receive high priority.