A 53-year-old man experienced a serious health problem when doctors gave him vitamin D supplements. He had a condition called primary hyperparathyroidism, where the parathyroid glands produce too much hormone and cause high calcium levels in the blood. His vitamin D was very low, which was hiding his calcium problem. When doctors fixed his vitamin D levels with supplements, his calcium suddenly became dangerously high. This case shows that doctors need to be careful when giving vitamin D to people with parathyroid problems, because it can unmask hidden calcium issues that need special treatment.

The Quick Take

  • What they studied: What happens when someone with a parathyroid gland problem gets vitamin D supplements to fix a vitamin D deficiency
  • Who participated: One 53-year-old man with primary hyperparathyroidism (overactive parathyroid glands) and severe vitamin D deficiency
  • Key finding: After taking vitamin D supplements, the patient’s blood calcium jumped from borderline-high (10.8 mg/dL) to dangerously high (14.4 mg/dL), requiring emergency medical treatment
  • What it means for you: If you have parathyroid problems and low vitamin D, talk to your doctor before starting vitamin D supplements. Your doctor may need to monitor your calcium levels closely during treatment to catch dangerous increases early.

The Research Details

This is a case report, which means doctors documented what happened to one specific patient. The patient came to the hospital with very high parathyroid hormone levels (639 pg/mL, which is much higher than normal) but only slightly elevated calcium levels. Blood tests also showed he had severe vitamin D deficiency (5 ng/mL, when normal is 30 ng/mL or higher). The doctors decided to treat his vitamin D deficiency by giving him cholecalciferol (vitamin D3) supplements. They monitored what happened to his calcium levels as his vitamin D improved.

A case report is like a detailed story about one patient’s medical experience. It’s useful for alerting doctors to unexpected problems or interesting patterns they might not have seen before. However, because it only involves one person, we can’t be sure the same thing would happen to everyone with this condition.

This case is important because it shows a hidden danger: vitamin D deficiency can actually mask (hide) high calcium problems in people with parathyroid disease. When doctors fix the vitamin D deficiency, the calcium problem suddenly becomes visible and dangerous. Understanding this connection helps doctors know when to be extra careful and watch calcium levels closely.

This is a single case report, which is the lowest level of scientific evidence. It describes one person’s experience, not a pattern seen across many patients. The information is valuable for warning doctors about a potential problem, but we would need larger studies with many patients to know how common this issue is or how often it happens.

What the Results Show

The main finding was that vitamin D supplementation caused a dramatic and dangerous increase in blood calcium levels. The patient’s calcium rose from 10.8 mg/dL (just slightly above normal) to 14.4 mg/dL (severely elevated) after vitamin D treatment. This happened because the vitamin D deficiency had been suppressing the calcium-raising effects of his overactive parathyroid glands. Once the vitamin D was restored to normal levels, the parathyroid glands’ full effect on calcium became apparent, causing a dangerous spike.

The patient’s parathyroid hormone level was extremely elevated at 639 pg/mL (normal is around 10-65 pg/mL). This very high hormone level, combined with only borderline-high calcium, was the clue that something unusual was happening. The severe vitamin D deficiency (5 ng/mL) explained why the calcium wasn’t as high as expected given the hormone levels.

Once the severe hypercalcemia developed, the patient required specific medical management to bring the calcium back down to safe levels. This case demonstrates that vitamin D supplementation can be a trigger for serious complications in people with parathyroid disease.

The case highlights how vitamin D deficiency can complicate the diagnosis of parathyroid disease. Doctors might miss or underestimate the severity of parathyroid problems when vitamin D is very low. The case also shows that the relationship between vitamin D, parathyroid hormone, and calcium is complex and interconnected—fixing one problem can unexpectedly worsen another.

This case adds to existing medical knowledge about how vitamin D and parathyroid disease interact. Doctors have known that vitamin D deficiency can increase parathyroid hormone levels, but this case illustrates a specific and serious risk: that correcting vitamin D deficiency in someone with undiagnosed or uncontrolled parathyroid disease can trigger a medical emergency. The case serves as a cautionary tale that fits with what we know about these conditions but highlights a specific scenario that doctors should watch for.

This is a report about just one patient, so we cannot know if this will happen to other people with the same condition. We don’t know how common this problem is or what percentage of parathyroid patients might experience this. The case doesn’t include information about whether the patient had any other health conditions that might have contributed to the problem. We also don’t have long-term follow-up information about what happened to this patient after treatment.

The Bottom Line

If you have been diagnosed with primary hyperparathyroidism or suspect you might have parathyroid problems, inform your doctor before starting vitamin D supplements. If you have both low vitamin D and parathyroid disease, your doctor should monitor your blood calcium levels frequently (possibly weekly or bi-weekly) during the early stages of vitamin D supplementation. This is a moderate-confidence recommendation based on this case report and general medical knowledge about these conditions.

This is most relevant to people who have been diagnosed with primary hyperparathyroidism or have symptoms suggesting parathyroid disease (like high calcium levels or high parathyroid hormone). It’s also important for doctors treating patients with parathyroid disease who also have vitamin D deficiency. People with normal parathyroid function and low vitamin D can generally take vitamin D supplements safely, but should still follow their doctor’s recommendations.

In this case, the dangerous calcium increase happened relatively quickly after starting vitamin D supplementation, though the exact timeline isn’t specified. This suggests that calcium levels should be checked within days to weeks of starting vitamin D treatment in at-risk patients, not just at routine follow-up visits months later.

Want to Apply This Research?

  • If you have parathyroid disease and are starting vitamin D supplementation, track your blood calcium levels weekly for the first month. Record the date, calcium level (in mg/dL), and any symptoms like nausea, weakness, confusion, or excessive thirst. Share these records with your doctor.
  • Set phone reminders for scheduled blood tests during vitamin D supplementation. Don’t skip appointments—early detection of calcium changes is critical. Also, keep a symptom log noting any unusual feelings, as severe high calcium can cause nausea, fatigue, or confusion.
  • Create a simple chart tracking: (1) vitamin D supplement dose and dates taken, (2) blood calcium levels and test dates, (3) parathyroid hormone levels if available, and (4) any symptoms experienced. Share this with your healthcare provider at each visit to identify patterns and catch problems early.

This case report describes one patient’s experience and should not be interpreted as medical advice. If you have been diagnosed with primary hyperparathyroidism, parathyroid disease, or have elevated calcium or parathyroid hormone levels, consult with your doctor before starting any vitamin D supplements or making changes to your treatment. Do not start, stop, or change any medications or supplements without medical supervision. This information is for educational purposes only and does not replace professional medical evaluation and care. Severe hypercalcemia is a medical emergency requiring immediate professional treatment.