What Causes Hypercalcemia?

Medically Reviewed by Zilpah Sheikh, MD on February 22, 2024
Written by Kim Painter, Keri Wiginton
7 min read

If your doctor tells you that you have hypercalcemia, it means you have too much calcium in your blood. The possible causes of high calcium levels include more than 25 diseases, as well as some medications, supplements, genes, and lifestyle factors.

You may not notice any symptoms if you have a mild case of hypercalcemia. But as your body tries to get rid of the extra calcium, you might pee a lot and get really thirsty. If your calcium levels are very high, you could get nervous system problems, including becoming confused and even passing out.

You'll usually find out that you have hypercalcemia through a blood test. If you don't get it treated, high levels of calcium in your blood can lead to bone loss, kidney stones, kidney failure, and heart problems.

Your doctor can help you get your calcium levels back to normal and figure out why they're out of whack in the first place.

While high blood calcium levels have many potential causes, about 90% of cases are linked to two causes: problems with the parathyroid glands or cancer. Here's what you need to know about the possible causes of high blood calcium levels.

Overactive parathyroid glands

The most common cause of high blood calcium levels is overactivity in one or more of these four glands, which sit behind your thyroid, in your neck.

If these glands are working right, they release parathyroid hormone (PTH) when your blood calcium levels get low. That's a signal for your bones to release more calcium into your blood, your kidneys to pee out less calcium, and your gut to absorb more.

But if you have overactive parathyroid glands, your body pumps out more PTH than you need and calcium builds up. This can happen if the glands grow too big or a noncancerous tumor forms on one or more of them.

If hyperparathyroidism is the cause of your high calcium, you may also get:

Your doctor will likely recommend surgery to remove the gland or glands causing the problem. A special scanning test can find which of the glands is malfunctioning before the surgery.

For mild cases, another option is to monitor your health, with regular checks of your blood calcium, blood pressure, kidneys, and bone health. You might also take drugs called calcimimetics to lower your PTH levels.

The doctor may also tell you to drink more fluids, exercise, stop taking some medicines, and temporarily lower the calcium in your diet.

Cancer

About 10%-30% of people with cancer may get hypercalcemia. That's because cancer can:

  • Cause your bones to break down and send calcium into your blood
  • Mimic your parathyroid hormone, which triggers the release of calcium from your bones
  • Affect your kidneys, which can lower the amount of calcium expelled when you pee

The most common cancer types that cause hypercalcemia include:

  • Lung cancer
  • Kidney cancer
  • Breast cancer
  • Multiple myeloma (a blood cancer that starts in the bone marrow)

Your cancer or the treatment you get for it can share symptoms with hypercalcemia, such as feeling sick or throwing up. If you get dehydrated, your kidneys can't get rid of calcium very well. Your doctor may give you fluids through a vein.

Hypercalcemia from cancer can be hard to manage. It helps to treat your cancer. But you may need drugs to slow the release of calcium from your bones, including:

  • Bisphosphonates, given through your veins
  • Denosumab (Prolia, Xgeva), given as a shot

Calcium supplements and hypercalcemia

The third most common cause of high blood calcium levels is the overuse of calcium carbonate, which many people take as both a calcium supplement and an antacid, to treat heartburn and indigestion. This particular form of calcium, when taken in very high doses, can directly raise calcium levels and damage kidneys, which may lead to even higher calcium levels. Doctors call this milk-alkali syndrome.

The treatment for this kind of high blood calcium is usually to stop taking the supplements and get plenty of fluids.

Calcium supplements and antacids are usually safe, as long as you don't overdo it and consider how much calcium you get from food as well. The recommended calcium intake for adults is 1,000-1,200 mg a day. The recommended upper limit is 2,500 mg a day for adults aged 19-50 and 2,000 mg a day for those aged 51 and older.

Vitamin D and hypercalcemia

Vitamin D helps regulate levels of calcium in your body. If you take extremely high doses of vitamin D, you may end up with very high levels of calcium in your blood. Taking 60,000 international units (IU) of vitamin D every day for several months -- far more than in standard supplements or fortified foods -- could cause this kind of overload. It's impossible to get that much Vitamin D from sun exposure or food.

To treat this problem, you'll need to stop taking vitamin D and restrict calcium in your diet for a while. You might also take medication, such as steroid pills, for a short time.

Vitamin A and hypercalcemia

Excess vitamin A can also result in high calcium levels. Vitamin A plays a role in bone building, but when you take too much, your bones release too much calcium and get weaker. Since too much vitamin A can hurt your health in several ways, doctors urge you to  stick to recommended daily intakes, which are 700 mcg REA (micrograms of retinol activity equivalents) for women and 900 mcg REA for men.

If your doctor finds high levels of vitamin A in your body, you'll need to stop taking any supplements containing the vitamin. You might also need to cut out foods high in vitamin A, such as liver and fortified foods.

Medications that cause hypercalcemia

Medications that might cause or worsen high calcium levels include:

  • Blood pressure drugs, such as thiazide diuretics, which can lower the amount of calcium that leaves your body when you pee
  • Lithium, which might affect your parathyroid glands and the amount of PTH they make

Your doctor may switch your medicine. If you need to stay on these drugs, they may give you medication to lower the amount of calcium in your blood.

Genetics and hypercalcemia

If you inherit a certain gene, your body misjudges how much calcium is in your blood. You'll send out more PTH than you need. It happens if you have a condition called familial hypocalciuric hypercalcemia (FHH). But in most cases, you won't have any symptoms or need treatment.

Your doctor may want to monitor your health. It's not common, but FHH can cause inflammation in your pancreas or calcium to build up in other parts of your body.

High calcium emergencies

If your calcium levels are very high, for any reason, you'll need to go to the hospital to get fluids and medicine called diuretics through your veins. This can treat hypercalcemia quickly.

Additional causes of hypercalcemia can include:

  • Health conditions. Lung diseases such as tuberculosis and sarcoidosis can raise your blood levels of vitamin D. In turn, your gut will absorb more calcium. Paget's disease and an overactive thyroid are also linked to hypercalcemia.
  • Inactivity. Your bones release calcium if you don't put your body weight on them. This can happen if you're paralyzed or you have an illness that keeps you in bed for a long time. Not getting enough exercise may also make hyperparathyroidism worse.
  • Serious dehydration. Your kidneys can't get rid of calcium if you don't have enough fluid in your body. An easy way to know if you're dehydrated is to look at your urine. You want it to be light yellow, not a shade of dark orange. You should drink fluids until you're not thirsty. Call a doctor if you have persistent diarrhea or vomiting and can't keep liquids down.

You are unlikely to get too much calcium, vitamin D, vitamin A, or other substances that lead to high blood calcium levels from foods alone. Usually, you need high doses of supplements to get into trouble.

One exception is betel nuts. These nuts, which are chewed as a stimulant in some regions of Asia, have been linked to high blood calcium levels, along with other harms to health.

Also, hypercalcemia has been reported in some children treated for years with a ketogenic diet, an eating plan with high levels of fat and low levels of carbohydrates. The diet may cause kidney damage, leading to high calcium levels.

If you already have high blood calcium, your doctor might ask you to cut back on certain foods until the dangerous levels fall.

Can drinking too much milk cause hypercalcemia?

In the past, some people who drank very large amounts of milk to try to treat stomach ulcers developed milk-alkali syndrome, the form of high blood calcium now usually linked to calcium supplements and antacids. Historical reports say these people drank more than 3 ounces of milk and cream every hour, along with doses of acid-reducing substances, such as sodium bicarbonate. The treatment didn't work and fell out of favor. Doctors rarely see such cases today.

If your doctor finds high calcium levels in your blood, it's probably not because you've been drinking too much milk or eating too much cheese. The most likely cause is a treatable problem with glands in your neck, called parathyroid glands. But there are many other possible causes, including some cancers and overuse of supplements, so it's important to work with your doctor to figure out the problem and get your calcium levels back to normal.

What is an alarming calcium level?

A normal range for total blood calcium in adults is usually between 8.5 and 10.3 milligrams/deciliter (mg/dL). So any level higher than that would be considered high and would likely lead your doctor to order more tests.

What organs does hypercalcemia affect?

Severe hypercalcemia is especially hard on your kidneys and heart. It can cause kidney failure and problems with your heart rhythms.