High calcium (hypercalcemia)

Short answer

Hypercalcemia is calcium in the blood rising above the normal range. The JAMA review reports that it is seen in about 1% of the world population and that in about 90% of cases the cause is primary hyperparathyroidism or a malignant disease. ^[1] It is not expected to develop from food alone; high-dose calcium or vitamin D supplements, however, can contribute. This page is for information, not for diagnosis and treatment; assessment belongs to a physician.

From how many mg/dL does high calcium begin?

Institutions do not use the same threshold, and the threshold depends on how the measurement is made. The NIH reports that serum total calcium in healthy people is generally between 8.8–10.4 mg/dL (2.2–2.6 mmol/L) and that it uses above 10.5 mg/dL (2.63 mmol/L) for hypercalcemia. The normal range of ionized (free) calcium in healthy people is given as 4.6–5.3 mg/dL (1.15–1.33 mmol/L). ^[2] EFSA’s summary report defines hypercalcemia as serum calcium above 2.75 mmol/L (11 mg/dL). ^[7]

The JAMA review separates severity as follows:

The review’s summary does not name the 12–14 mg/dL range as a separate class; the lower bound of the “mild” class is the hypercalcemia threshold (above 10.5 mg/dL according to the NIH, above). ^[1] About half of the calcium in blood is bound to protein and the free ionized portion is biologically active; therefore total calcium must be corrected for albumin level before a diagnosis of hypercalcemia is made. In critically ill patients, because changes in blood pH affect calcium binding to albumin, measurement of ionized calcium is recommended. ^[5]

What causes hypercalcemia?

According to the JAMA review, about 90% of cases are due to primary hyperparathyroidism (excess parathyroid hormone secretion by the parathyroid glands) or malignancy. Less common causes include granulomatous diseases such as sarcoidosis, endocrine disorders such as thyroid diseases, prolonged immobility, genetic diseases, medicines (such as thiazide-group diuretics) and supplements (calcium, vitamin D or vitamin A). The review also mentions some newer medicine classes and rare situations (such as a ketogenic diet, excessive exercise) and states that together these make up less than 1% of causes. ^[1]

The NIH also says that hypercalcemia and excess urinary calcium (hypercalciuria; urinary calcium above 250 mg per day in women and 275 mg in men) are uncommon in healthy people and mostly stem from cancer, primary hyperparathyroidism and similar conditions. The NIH also states that long-term use of lithium, used in bipolar disorder, can cause hypercalcemia and that use together with calcium supplements may increase this risk. ^[2] In 2022, the guideline of the Fifth International Workshop, attended by more than 50 experts, was published for the evaluation and management of primary hyperparathyroidism; the summary statement notes that, unlike the previous 2014 guideline, kidney-related criteria were revised. The decision for surgery or monitoring is made by a physician according to these expert guidelines. ^[3]

Supplements and milk-alkali syndrome

EFSA reports that hypercalcemia is not expected to develop from food alone, but can occur with high-dose calcium supplements, particularly when used together with vitamin D supplements. ^[7] In a Cochrane review (fracture prevention trials in older adults), mild hypercalcemia, mostly in the 2.6–2.8 mmol/L range, was seen more often in those taking vitamin D or an analogue (with or without calcium) than with placebo (21 trials, 17,124 participants; RR 2.28; 95% CI 1.57–3.31). ^[6]

Milk-alkali syndrome consists of hypercalcemia, kidney failure of varying degrees and metabolic alkalosis, and is due to intake of large amounts of calcium and absorbable alkali. According to the review by Medarov, this picture, which arose from the use of milk and alkali in treating peptic ulcer in the early 20th century, became rare with drug therapies but has begun to be seen again because of the widespread use of calcium carbonate, mostly for osteoporosis prevention. Treatment is supportive and includes correcting dehydration and stopping the responsible substances. ^[4]

Detailed guideVitamin D excess: symptoms, upper limit and what a high value means→

Upper limit and overlooked sources

The US upper limit (UL) cited by the NIH is 2,000–2,500 mg per day in adults depending on age and covers total calcium from foods and supplements. Some antacid chewable tablets contain calcium carbonate and provide about 270–400 mg of calcium per tablet; when a supplement, multivitamin and antacid are used together, total intake can therefore rise unnoticed. ^[2] The fact that Medarov’s review attributes the reappearance of milk-alkali syndrome to the widespread use of calcium carbonate shows why this total matters. ^[4]

What are the symptoms of hypercalcemia?

Mild hypercalcemia is mostly symptom-free; according to the JAMA review, about 20% of people may have general complaints such as fatigue and constipation. Hypercalcemia that is severe or develops rapidly over days to weeks can lead to nausea, vomiting, thirst (dehydration), confusion, drowsiness and coma. ^[1]

The NIH reports that hypercalcemia and hypercalciuria can cause decreased muscle tone, kidney failure, low phosphate, constipation, nausea, weight loss, fatigue, frequent urination and heart rhythm disorders, and are associated with the risk of cardiovascular death. ^[2] None of these symptoms is specific to hypercalcemia; a diagnosis cannot be made from symptoms without a blood test.

How is hypercalcemia investigated?

First, blood calcium is confirmed with albumin correction or as ionized calcium. According to the JAMA review, the first and most important additional test is serum intact parathyroid hormone (PTH): in a person with hypercalcemia, a high or normal PTH is consistent with primary hyperparathyroidism; a suppressed PTH (below about 20 pg/mL depending on the test method) points to another cause. ^[1] This distinction determines which tests (such as medicine and supplement history, vitamin D level, imaging) will be requested in the second step; the physician makes this decision.

How is it managed?

Treatment varies by cause and level and is planned by a physician. According to the JAMA review, mild hypercalcemia mostly does not require urgent intervention. In symptomatic or severe hypercalcemia, initial treatment is fluid therapy (hydration) and intravenous bisphosphonates; in conditions due to excess intestinal absorption (vitamin D poisoning, granulomatous diseases, some lymphomas), glucocorticoids may be used. In primary hyperparathyroidism, parathyroidectomy is considered according to age, calcium level and kidney or skeletal involvement; over age 50, if the calcium level is less than 1 mg/dL above the upper limit of normal and there is no skeletal or kidney disease, monitoring may be appropriate. ^[1]

Which treatment will be chosen in whom, whether a supplement or medicine will be stopped, and the frequency of follow-up are personal decisions; this page gives no program for these.

In which situations is urgent assessment needed?

In a person with known or suspected high calcium, symptoms such as repeated vomiting, marked thirst, confusion, excessive sleepiness or clouding of consciousness may be signs of severe hypercalcemia and require urgent medical assessment. ^[1] A high value found incidentally without symptoms, while not urgent, requires physician assessment to investigate its cause; in this assessment, all products used such as calcium, vitamin D, vitamin A and antacids, and medicines such as thiazide or lithium, are reviewed.

Detailed guideCalcium guide: roles, reference intakes and supplement safety→ Detailed guideCalcium deficiency symptoms: are hypocalcemia and low intake the same thing?→ Detailed guideWhich foods contain calcium? Serving table and absorption→

Main guide: What is calcium? This guide does not recommend personal doses.