Radioactive iodine therapy for overactive thyroid can temporarily damage parathyroid glands, causing severe low blood calcium that requires hospitalization and long-term supplementation. According to research reviewed by Gram, one 66-year-old patient developed dangerously low calcium (0.70 mmol/L) two weeks after treatment and remained dependent on calcium and vitamin D supplements nine months later, suggesting this complication may be underrecognized and warrants routine monitoring after radioactive iodine therapy.
A 66-year-old woman developed severe low blood calcium levels two weeks after receiving radioactive iodine treatment for an overactive thyroid (Graves’ disease). According to research reviewed by Gram, her parathyroid glands, which control calcium levels, temporarily stopped working properly. She needed calcium and vitamin D supplements in the hospital and continued needing them nine months later. This case report highlights that doctors should watch patients more carefully after radioactive iodine therapy, checking their calcium and parathyroid hormone levels regularly, since parathyroid damage may be more common than previously recognized.
Key Statistics
A 2026 case report documented a 66-year-old woman who developed severe hypocalcemia (0.70 mmol/L) two weeks after receiving 555 MBq radioactive iodine therapy for Graves’ disease, requiring hospitalization and remaining dependent on calcium and vitamin D supplementation at 9-month follow-up.
In this case report, the patient’s parathyroid hormone levels remained low despite severe hypocalcemia, indicating parathyroid gland dysfunction rather than other causes of low calcium, and recovery was prolonged with calcium levels stabilizing only with ongoing supplementation.
The patient progressed from initial paresthesia and muscle cramps to hospitalization within one week, demonstrating the rapid and severe progression of symptomatic hypocalcemia following radioactive iodine therapy for Graves’ disease.
The Quick Take
- What they studied: Whether radioactive iodine treatment for overactive thyroid can damage the parathyroid glands and cause dangerously low blood calcium levels
- Who participated: One 66-year-old woman with a 30-year history of Graves’ disease (overactive thyroid) who received radioactive iodine therapy
- Key finding: Two weeks after radioactive iodine treatment, the patient developed severe low blood calcium (0.70 mmol/L) due to temporary parathyroid gland dysfunction, requiring hospitalization and long-term calcium and vitamin D supplements
- What it means for you: If you receive radioactive iodine therapy for thyroid problems, ask your doctor to monitor your calcium and parathyroid hormone levels regularly for at least several months afterward. Report muscle cramps, tingling, or numbness immediately, as these may signal dangerous calcium drops
The Research Details
This is a case report, meaning doctors documented what happened to one specific patient rather than comparing large groups of people. The patient received a standard dose of radioactive iodine (555 MBq) to treat her overactive thyroid. Doctors then tracked her blood tests and symptoms over time, including calcium levels, vitamin D, and parathyroid hormone measurements.
Case reports are like detailed medical stories, they’re useful for spotting unexpected side effects that larger studies might miss. In this case, the doctors noticed that the parathyroid glands (four tiny glands in the neck that control calcium) seemed to stop working after the radioactive iodine treatment. They documented exactly when symptoms appeared, how severe they were, and how long recovery took.
This type of study is particularly valuable when a side effect is rare or unexpected, because it allows doctors to describe the full picture of what happened to one person in detail, which can alert other doctors to watch for similar problems in their patients.
Radioactive iodine therapy is a common, well-established treatment for overactive thyroid, and doctors generally consider it safe. However, this case suggests that parathyroid damage might happen more often than doctors realize, because it’s not routinely monitored. By documenting this detailed case, the doctors are essentially saying: ‘Watch out for this problem: it might be more common than we thought.’ This matters because low blood calcium can cause serious symptoms like seizures or heart problems if not treated quickly.
This is a single case report, which is the lowest level of scientific evidence. It describes one person’s experience, not a pattern across many patients. However, the doctors provided detailed medical records, lab values, and follow-up information over 9 months, which makes the documentation reliable. The main limitation is that we can’t know if this happens to other patients too, or how often it occurs. Larger studies would be needed to determine if parathyroid damage is a common side effect or a rare coincidence.
What the Results Show
The patient developed severe symptoms of low blood calcium starting two weeks after radioactive iodine treatment. She experienced tingling sensations (paresthesia) and muscle cramps that got progressively worse. One week later, she was hospitalized because her symptoms had become severe enough to require emergency care.
Blood tests confirmed that her calcium level had dropped dangerously low (0.70 mmol/L, normal is around 2.2-2.6 mmol/L). Her parathyroid hormone level was also low, indicating that her parathyroid glands weren’t responding normally to the low calcium. She also had vitamin D deficiency, which made the problem worse since vitamin D helps the body absorb and regulate calcium.
The patient required intravenous (IV) calcium given directly into her veins in the hospital, followed by oral calcium and vitamin D supplements. Over the following months, her calcium levels gradually improved but remained low enough that she needed to continue taking supplements. At the 9-month follow-up visit, her calcium levels were stable only because she was still taking the supplements, suggesting her parathyroid glands had not fully recovered.
Nine months after the radioactive iodine treatment, the patient also developed hypothyroidism (an underactive thyroid), which is a known side effect of radioactive iodine therapy. This suggests that the radiation affected not just the parathyroid glands but also the thyroid tissue itself, which is expected. The combination of parathyroid dysfunction and hypothyroidism means this patient required ongoing monitoring and multiple medications to manage both conditions.
Radioactive iodine therapy has been used for decades, and doctors know it can cause hypothyroidism (underactive thyroid) as a delayed side effect. However, parathyroid damage is not routinely discussed or monitored after this treatment. This case suggests that parathyroid dysfunction may be an underrecognized complication. Previous medical literature has documented rare cases of parathyroid damage after radioactive iodine, but it’s not considered a common or expected side effect, which is why many doctors don’t routinely check for it.
This is a single case involving one patient, so we cannot determine how often this complication occurs or whether it’s rare or common. We don’t know if other patients experienced similar problems but weren’t diagnosed because doctors weren’t looking for it. The patient had a 30-year history of Graves’ disease and had been treated with multiple medications before receiving radioactive iodine, so it’s unclear whether the radioactive iodine alone caused the parathyroid problem or if previous treatments contributed. Without studying many more patients, we can’t establish clear risk factors or predict who might be at higher risk for this complication.
The Bottom Line
If you’re scheduled for radioactive iodine therapy for an overactive thyroid: (1) Ask your doctor to check your calcium and parathyroid hormone levels before treatment as a baseline; (2) Request follow-up blood tests at 2 weeks, 1 month, 3 months, and 6 months after treatment; (3) Report any muscle cramps, tingling in your fingers or lips, or numbness immediately; (4) Ensure you have adequate vitamin D levels before treatment. Confidence level: Moderate, based on this single case, but supported by the principle that monitoring for known complications is good medical practice.
Anyone scheduled for radioactive iodine therapy should discuss this potential complication with their doctor. People with existing vitamin D deficiency, kidney disease, or those taking medications that affect calcium metabolism should be especially vigilant. Doctors treating thyroid patients should consider adding parathyroid monitoring to their standard post-treatment follow-up. This case is less relevant to people taking other thyroid treatments like medications or surgery.
In this case, symptoms appeared within 2 weeks of treatment and required hospitalization within 3 weeks. Recovery was slow, calcium levels remained abnormal at 9 months and required ongoing supplementation. If you receive radioactive iodine therapy, expect your doctor to monitor you for at least 6-9 months, and possibly longer.
Frequently Asked Questions
Can radioactive iodine therapy damage your parathyroid glands?
Yes, this case report shows that radioactive iodine therapy can temporarily damage parathyroid glands, causing severe low blood calcium. A 66-year-old patient developed dangerously low calcium (0.70 mmol/L) two weeks after treatment and required ongoing supplementation for at least 9 months.
What are the symptoms of low calcium after thyroid treatment?
Symptoms include tingling in fingers and lips, muscle cramps, numbness, and in severe cases, muscle spasms or seizures. This patient experienced progressive symptoms starting two weeks after radioactive iodine therapy and required hospitalization within three weeks.
How long does parathyroid recovery take after radioactive iodine?
Recovery appears to be prolonged. In this documented case, the patient’s parathyroid function had not fully recovered nine months after treatment, and she remained dependent on calcium and vitamin D supplements to maintain normal blood calcium levels.
Should I get blood tests after radioactive iodine therapy?
Yes, this case highlights the importance of monitoring calcium and parathyroid hormone levels after radioactive iodine therapy. Doctors should check these levels at 2 weeks, 1 month, 3 months, and 6 months post-treatment to catch parathyroid problems early.
Is parathyroid damage a common side effect of radioactive iodine?
This case suggests parathyroid damage may be underrecognized, but it’s not routinely monitored. We don’t know how common it is because doctors typically don’t check for it. More research is needed to determine the actual frequency of this complication.
Want to Apply This Research?
- If you’ve had radioactive iodine therapy, track your symptoms weekly: muscle cramps (0-10 scale), tingling sensations (present/absent), energy levels, and any new symptoms. Log these in your health app alongside your calcium and vitamin D supplement doses to identify patterns.
- Set phone reminders to take calcium and vitamin D supplements at the same time daily. Use your app to log each dose and any symptoms that day. This creates a clear record to share with your doctor and helps you notice if symptoms worsen when you miss doses.
- Schedule quarterly blood work reminders in your app for the first year after radioactive iodine therapy. Track the results (calcium, ionized calcium, parathyroid hormone, vitamin D) in your health records. Create a chart showing trends over time. If any value starts moving in the wrong direction, alert your doctor immediately rather than waiting for your next scheduled appointment.
This case report describes one patient’s experience and should not be interpreted as medical advice. Radioactive iodine therapy remains a standard, generally safe treatment for overactive thyroid. However, this case highlights the importance of monitoring for parathyroid complications. If you are scheduled for radioactive iodine therapy or have received it recently, discuss parathyroid monitoring with your doctor. If you experience muscle cramps, tingling, numbness, or other concerning symptoms after thyroid treatment, seek medical attention immediately. Do not start or stop any medications or supplements without consulting your healthcare provider. This information is for educational purposes and does not replace professional medical evaluation.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.
