High calcium levels in the blood (hypercalcemia) are not as common as low levels but often signal serious medical conditions. The most common causes of hypercalcemia are hyperparathyroidism and cancer. Read to understand what else can cause your blood calcium levels to rise too high.

What is Hypercalcemia?


Hypercalcemia is excessively high calcium levels in the blood (“hyper” = high, “calcemia” = calcium in the blood). Chronic hypercalcemia carries several health risks, including poor kidney function, heart disease, coma, and even death [1, 2, 3].

Hypercalcemia is most often caused by an underlying disease (see “Causes” below).

Taking in more calcium from food and supplements is unlikely to substantially raise your blood levels. It may cause other problems, such as constipation, or reduce the absorption of other minerals (including iron and zinc). But since calcium is the most abundant mineral in the body, its levels are tightly controlled independently of your dietary intake [1, 4].


Common symptoms of hypercalcemia levels include [5]:

  • Abdominal pain
  • Nausea & vomiting
  • Excessive thirst
  • Frequent urination
  • Muscle aches
  • Confusion
  • Coma

Hypocalcemia can be dangerous and you should seek urgent medical help if you experience the listed symptoms.

Calcium Blood Test

A calcium test measures your calcium levels in the blood. Most commonly, the test estimates your total serum calcium levels and includes [6, 7]:

  • Calcium bound to proteins, mainly albumin (about 40%)
  • Calcium complexed with phosphate and citrate (about 10%)
  • Ionized calcium, also known as free or active calcium (about 50%)

You don’t need to prepare for this test or fast beforehand. A healthcare professional will simply collect a blood sample that will be analyzed.

The calcium blood test is often done as part of a routine metabolic panel. The basic metabolic panel (BMP) checks blood sugar, calcium, and electrolytes, as well as kidney function. The comprehensive metabolic panel (CMP) also includes cholesterol, protein levels, and markers of liver function [8].

Your doctor may also order an ionized (free) calcium test.

Ionized calcium is the body’s active form of calcium. It is assumed to be around 50% of the total blood calcium, although the exact percentage may vary. Ionized calcium levels are often just estimated based on total blood calcium and albumin levels. Testing ionized calcium is far more precise, but it requires special equipment and is expensive [6].

High Calcium Levels

The normal range of blood calcium is 8.5 to 10.5 mg/dL. These values can vary slightly from lab to lab. Hypercalcemia is defined as total blood calcium over 10.5 mg/dL [9, 10, 11]:

  • 10.51 – 12 mg/dL is considered mild hypercalcemia and usually doesn’t cause symptoms
  • 12 – 13 mg/dL is considered moderate hypercalcemia
  • 13 mg/dL and above is considered severe hypercalcemia

Hypercalcemia Causes

1) Hyperparathyroidism

Calcium blood levels are mostly controlled by parathyroid hormone (PTH). Cells in your parathyroid gland — located in the neck just behind the thyroid – release PTH when they sense a drop in calcium blood levels [12].

PTH raises blood calcium levels by increasing the absorption of calcium from the gut and kidneys. This hormone also mobilizes calcium and phosphate from the bones: that is, it breaks down and frees the mineral content of bones to compensate for low calcium levels. This process is also known as bone resorption [12].

PTH also increases the amount of vitamin D that is converted to its active form, calcitriol. Active vitamin D increases calcium absorption in the gut [12].

If PTH levels get too high, calcium levels will also spike.

Hyperparathyroidism or an overactive parathyroid gland is the most common cause of hypercalcemia. This can happen when one or more of the parathyroid glands become enlarged, either benignly or due to cancer [13, 14].

This condition is often missed by primary doctors, even when calcium levels are too high (over 10.5 mg/dL). According to one study, above-range calcium levels were missed or ignored in 58% of cases. Even when both calcium and PTH were above range, a diagnosis was missed in 28% of cases. Women were more likely than men to have their symptoms ignored [15].

Another study found that a diagnosis of hyperparathyroidism was missed in 40% of cases, even when both calcium and PTH were elevated beyond the normal range. Hypercalcemia was often ascribed to other causes than hyperparathyroidism, including diuretics (12%), calcium supplements (12%), dehydration (5%), and kidney dysfunction (3%) [16].

2) Cancer

Aside from cancer of the parathyroid gland, other types of cancers can cause hypercalcemia by releasing a protein that mimics PTH. These include lung, ovary, and kidney cancer. Cancers that spread to the bones and go on to damage bone cells can excessively raise blood calcium levels [13, 14, 17, 2].

3) Certain Drugs

Certain medications may cause (or contribute to) hypercalcemia. These include [14, 17, 18, 19, 20, 21]:

  • Lithium
  • Theophylline
  • Thiazide diuretics – used to treat high blood pressure
  • Androgens, used in breast cancer therapy
  • Estrogens, such as in birth control pills
  • Anti-estrogens – used to treat breast cancer and hormonal abnormalities
  • Tamoxifen (Nolvadex), used against breast cancer
  • Antacids for heartburn such as Tums

4) Vitamin D Overdose

An overdose of vitamin D can cause hypercalcemia. This condition is known as hypervitaminosis D.

Vitamin D can raise calcium levels since it increases the amount of calcium absorbed in the gut. According to the literature, this might happen only if you take 20,000 – 100,000 IU per day for at least a month for this to occur–this is 2-10X the maximum safe dose of vitamin D (10,000 IU) [17, 22, 23, 24].

Importantly, sun exposure doesn’t cause dangerously high vitamin D (or calcium). Even if you get too much sun, the sunlight will degrade any excess vitamin D and prevent hypervitaminosis [25].

The only risk of overdose comes from megadosing vitamin D supplements.

5) Vitamin A Overdose

Vitamin A overdose can also lead to hypercalcemia. This usually only happens if you take high-dose vitamin A supplements for a long time.

As to how much is too much, extremely large doses cause acute poisoning (25,000 IU/kg body weight). Chronic toxicity, however, is more subtle; it may occur with doses about 10 times higher than the recommended daily allowance (~ 7,000 IU/day) over a longer period of time [26].

Supplements usually take the blame for poisoning. But constantly eating large amounts of food concentrated in vitamin A, such as beef liver, might also be risky. Pregnant women should be especially mindful about this. The RDA of vitamin A for adults is 900 mcg RAE [27, 28, 26, 29, 30].

5) Addison’s Disease

Addison’s disease, also known as adrenal insufficiency, is another cause of hypercalcemia. Scientists are still exploring the exact mechanism, but it’s likely that the kidneys become less efficient at removing calcium; at the same time, more calcium is released from the bones [31, 32, 33].

6) Hyperthyroidism

An overactive thyroid (hyperthyroidism) can sometimes cause hypercalcemia too. The mechanism is poorly understood. Some evidence suggests the following changes occur in hyperthyroidism:

  • Increased sensitivity of bone to PTH
  • Increased interleukin-6 (IL-6) levels and sensitivity
  • Dysregulation of adrenal hormones

The result of these changes is an increased mobilization of calcium and phosphate from bones (bone resorption) [13, 34, 35, 36, 37].

7) Sarcoidosis

Hypercalcemia is a complication of sarcoidosis, an inflammatory disease that attacks several organs in the body. In sarcoidosis, the production of active vitamin D is out of control while parathyroid hormone levels can also be increased. This causes calcium levels to surge [38, 39, 40, 41, 42].

8) Other

High calcium levels may also be due to:

  • Tuberculosis [43]
  • Kidney disease [19]
  • HIV/AIDS [44]
  • Dehydration [45]
  • Being bedridden for a long time (immobilization) [19]

9) Consuming Too Much Calcium

As mentioned, this one is uncommon but possible. It has been reported in people who take large doses of calcium carbonate (4-60 g daily) along with alkaline substances, such as milk, bicarbonate or antacids. The system becomes overwhelmed and cannot excrete the calcium fast enough. The phenomenon is known as milk-alkali syndrome [46, 21].

Tolerable Upper Intake Levels (ULs) for Calcium

Below are shown the maximum daily level of calcium that you should not go beyond. This includes calcium from foods as well as supplements. Going over this level for a short while is unlikely to cause any issues, but doing so long term is unsafe [1].

0–6 months1,000 mg1,000 mg
7–12 months1,500 mg1,500 mg
1–8 years2,500 mg2,500 mg
9–18 years3,000 mg3,000 mg3,000 mg3,000 mg
19–50 years2,500 mg2,500 mg2,500 mg2,500 mg
51+ years2,000 mg2,000 mg

The Importance of Getting Enough Magnesium

Magnesium is necessary for regulating calcium levels in the blood. It is also a co-factor in the production and activation of vitamin D. The ratio of calcium to magnesium is important, and most people don’t get enough magnesium compared to calcium [47].

Evidence suggests that the optimal ratio is 2:1, meaning that you need twice as much calcium as magnesium. Meanwhile, getting more than that – for example, 4 times more calcium than magnesium–has been linked to numerous chronic diseases [47].

It turns out that our modern lifestyle has shifted the balance in favor of calcium. It’s extremely important to create a mindful, balanced diet for yourself with the right quantities of both minerals. Alternatively, you can also supplement with magnesium [47].

Hypercalcemia in Dogs and Cats

Dogs and cats can also get hypercalcemia, roughly for the same reasons as humans. Frequent symptoms of hypercalcemia in dogs and cats include [48]:

  • Excessive thirst
  • Frequent urination
  • Anorexia
  • Lethargy

If you suspect your cat or dog has hypercalcemia, take them to a veterinarian as soon as possible.

Hypercalcemia Treatment

Chronic or severe hypercalcemia should always be treated by a doctor. There may be serious underlying medical conditions that you don’t want to miss.

If you have mild or temporary hypercalcemia, there are several steps you can take.

First of all, avoid calcium-containing supplements, including over-the-counter drugs for heartburn (such as Tums). You should also stop taking vitamin D supplements.

Secondly, reduce foods high in calcium: dairy, tofu, fortified cereals, and green leafy vegetables [49, 50].

Up your intake of low-calcium foods instead. Some low-calcium food options include olive oil, resistant starch, rice, apples, tomatoes, eggplant, strawberries, and asparagus.

Last but not least, drink more water. Staying properly hydrated is important for maintaining healthy calcium levels.


Did you know that you can analyze your calcium lab test results with Lab Test Analyzer? It gives you natural recommendations and tells you if your values are above or in the range you need for optimal health.  

LabTestAnalyzer is a sister company of SelfHacked. The proceeds from your purchase of this product are reinvested into our research and development, in order to serve you better. Thank you for your support.


High blood calcium levels are usually due to an underlying disease. The two most common causes are an overactive parathyroid gland and cancer. Your doctor will determine your levels by running a calcium blood test, along with other markers if needed.

Certain drugs, as well as high vitamin A and vitamin D intake, may also cause hypercalcemia.

Consuming too much calcium is unlikely to raise your blood levels. However, diets high in calcium and low in magnesium may increase your risk of chronic diseases. Make sure you get enough magnesium through food or supplements.

If your blood calcium is high, seek medical help. Drink plenty of water, stop taking calcium-containing and vitamin D supplements, and add foods lower in calcium to your diet.

About the Author

Jimmy Julajak, MSc

MS (Psychology)

Jimmy got his MSc from the University of Copenhagen.

Jimmy is a psychologist and researcher. He is particularly interested in the workings of the brain and strategies for improving brain health. He believes that people shouldn't hand over the responsibility for their health only to their doctors. His aim is to empower each person with easy-to-understand, science-based health knowledge.

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