Radioactive iodine-131 destroys thyroid follicular cells by emitting ionizing radiation that damages their DNA and cellular structures.

We analyzed the available evidence and found that radioactive iodine-131 destroys thyroid follicular cells by emitting ionizing radiation that damages their DNA and cellular structures [1]. This happens because the thyroid naturally absorbs iodine to make hormones, and when iodine-131 is taken in, it gets pulled into the same cells. Once inside, the radiation it gives off breaks apart molecules in the cell, especially DNA, which disrupts normal function and leads to cell death over time. The damage is targeted because other tissues in the body don’t absorb iodine the same way, so most of the radiation stays within the thyroid. What we’ve found so far is consistent across all the evidence we’ve reviewed — there are no studies in our analysis that contradict this mechanism. The process doesn’t happen instantly; it unfolds over days to weeks as the cells try and fail to repair the radiation damage. This is why iodine-131 is used in medical settings to reduce overactive thyroid tissue or remove remaining thyroid cells after surgery. For someone considering this treatment, it means the therapy works by using the thyroid’s own biology to deliver radiation precisely where it’s needed, minimizing impact on the rest of the body.