Hypercalcemia and hypocalcemia: What you need to know

From the desk of
Luis Villaseñor
ScienceHypercalcemia and hypocalcemia: What you need to know

Hypercalcemia and hypocalcemia are serious medical conditions with serious consequences. If a calcium imbalance becomes severe enough, it can be life-threatening.

Fortunately, these imbalances are relatively rare in healthy people. They aren’t everyday occurrences.

Contrary to popular belief, insufficient dietary calcium is NOT a primary cause of hypocalcemia. When you don’t consume enough calcium, you just pillage bone to normalize serum levels.

A similar principle applies to hypercalcemia. If you consume too much dietary calcium, your body twists other dials: it increases urinary excretion, decreases gut absorption, and slows bone shedding to restore calcium to normal ranges.

Calcium supplements are a possible exception. They can temporarily overwhelm your calcium maintenance system, spike serum calcium, and increase arterial calcification. I’ll spend more time on this later.

I’ll also explain the distinction between hypercalcemia, hypocalcemia, and calcium deficiency. By the end of the article, you’ll understand why your serum calcium is actually not a good indicator of your overall calcium status.

First, though, I want to cover the basics of calcium and calcium imbalances. Let’s dive in.

Calcium 101

Calcium is a mineral that wears many hats in the human body. These hats can be lumped into two main categories:

  1. Skeletal structuring
  2. Electrolyte-related roles

When most people think of calcium, they think of bone health. About 99% of your bodily calcium is found in bones, teeth, and other hard tissue.

How calcium enters and exits bone is a complex dance, and the main dancers are calcium, vitamin D, phosphorus, calcitonin, and parathyroid hormone (PTH). I’ll be referring to these nutrients and hormones throughout the article, but for now I’ll make a couple of key points:

  • Adequate calcium and vitamin D levels suppress PTH, which curbs bone shedding.
  • Vitamin D also facilitates calcium absorption in the gut.
  • Vitamin D deficiency, calcium deficiency, and phosphorus overload elevate PTH, which in turn increases bone shedding.
  • Calcium overload elevates calcitonin, which shuts down calcium loss from bone.

Calcium is also an electrolyte (charged mineral) that enables cellular communication in the brain, heart, and skeletal muscles. Blood calcium plays other roles too (enzymatic activity, coagulation, etc.), but for now, understand that maintaining serum calcium levels (as opposed to maintaining bone calcium) is your body’s priority.

What Is Hypercalcemia?

Hypercalcemia is defined as a serum calcium level above 10.5 mg/dL. At levels of 14.0 mg/dL and above, it’s considered a hypercalcemic crisis.

Overt symptoms of hypercalcemia typically crop up around 12 mg/dL. Remember them with this handy rhyme: groans, bones, stones, moans, thrones, and psychic overtones.

  • Groans: nausea, vomiting, stomach pain, and other GI symptoms
  • Bones: bone pain and disorders of bone density (like osteoporosis) that increase fracture risk
  • Stones: kidney stones
  • Moans: feeling low energy, lousy, and tired
  • Thrones: constipation on “the throne”
  • Psychic overtones: confusion, depression, and memory loss

Severe hypercalcemia can also impact heart function, leading to arrhythmias, bradycardia (slow heart rate), and other disturbances noticeable via EKG. General muscle weakness is another classic symptom.

Although not technically a symptom, soft tissue calcification is perhaps the most insidious consequence of hypercalcemia. We want calcification to happen in the skeleton, not in the blood vessels where it accelerates the progression of heart disease.

What Causes Hypercalcemia?

About 1 to 2% of the general population suffers from hypercalcemia. The explanation usually ties back to PTH or vitamin D. Let’s explore that in more detail.

Causes of Hypercalcemia:

  • Primary hyperparathyroidism. A condition suffered by 0.2 to 0.8% of the population in which the parathyroid gland overproduces PTH. The common fix, unfortunately, is to remove the gland.
  • Cancer. About 2% of all cancers—including leukemia, renal carcinomas, and lymphomas—are associated with hypercalcemia. Cancer tends to disturb PTH levels.
  • Vitamin D toxicity. Excess vitamin D increases calcium absorption and spikes serum calcium levels. Most cases of vitamin D-related hypercalcemia are seen at 25(OH)D levels higher than 200 ng/mL.
  • Other causes. Kidney failure, use of diuretics, vitamin A toxicity, milk-alkali syndrome, and prolonged immobilization.

Excess calcium intake can also cause hypercalcemia, but (assuming functional calcium homeostasis) this should be a temporary situation.

What Is Hypocalcemia?

Hypocalcemia is defined as serum calcium levels below 8.5 mg/dL. Though less common than hypercalcemia, it can be life-threatening if not addressed and treated with IV or oral calcium.

The symptoms of hypocalcemia include:

  • Tetany
  • Muscle spasms
  • A feeling of pins and needles (paresthesias)
  • Hand and wrist spasm (carpopedal spasm)
  • Anxiety, depression, or mood swings
  • Seizures
  • Irregular heartbeat (can be fatal in severe cases)

When diagnosing hypocalcemia, clinicians look for these symptoms in conjunction with the following possible causes.

What Causes Hypocalcemia?

According to NIH StatPearls, renal failure is the leading cause of hypocalcemia. When the kidneys fail, vitamin D isn’t properly metabolized and phosphorus isn’t properly excreted. This leads to lower calcium levels.

Vitamin D deficiency is the second leading cause of hypocalcemia. When you don’t get enough D, you can’t properly absorb calcium through the intestines.

The best sources of vitamin D are the sun, fortified dairy, and vitamin D supplements. Even though vitamin D pills are cheap, ubiquitous, and effective, about 42% of Americans are deficient.

Other possible causes of hypocalcemia include:

  • Hypomagnesemia or hypermagnesemia (high or low serum magnesium)
  • Low parathyroid hormone (PTH) due to parathyroidectomy, autoimmunity, or various conditions that affect the parathyroid gland. Remember, PTH helps shuttle calcium out of bone and into the blood.
  • Alkalosis (calcium levels depend on serum pH)
  • Acute pancreatitis
  • Sepsis
  • Phosphorus overload
  • Drugs that increase bone reabsorption of calcium or decrease PTH secretion. (The chemotherapeutic drug Cisplatin can also cause hypocalcemia.)
  • Osteoblastic metastases

Why isn’t low dietary calcium listed? Let’s discuss.

Calcium Imbalance vs Calcium Deficiency

A calcium imbalance is distinct from a calcium deficiency. This is a critical point.

A calcium imbalance occurs when serum calcium levels get too high (hypercalcemia) or too low (hypocalcemia). This imbalance will show up on a blood test and often requires medical attention.

A calcium deficiency occurs when you don’t consume enough calcium. There are consequences, but they typically aren’t acute and/or life-threatening like with electrolyte imbalances.

The main consequence of calcium deficiency is poor bone density and increased fracture risk. (Osteoporosis). Why? Because bone is your body’s calcium reservoir.

When you consume sufficient calcium, the reservoir stays full. When you don’t, the reservoir gets depleted to maintain serum calcium.

The way your body looks at it, serum calcium is ALWAYS the priority. Serum calcium regulates basic functions like muscle contraction, neural transmission, heartbeat, blood clotting, and more. These functions are not optional. As you’ll recall, things get pretty hairy when serum levels fluctuate.

Bone calcium plays second fiddle to serum calcium. Osteoporosis is a progressive degeneration; not a survival emergency.

The takeaway? A serum calcium test DOES NOT validly assess calcium status. It just tells you that your calcium regulation system is working.

Getting Your Daily Calcium

For healthy bones, adults should aim for around a gram of calcium per day. Teenagers and postmenopausal women need a bit more, and young children a bit less. See this fact sheet for exact doses.

I advise getting all of your daily calcium from dietary sources. Skip the supplements.

I already mentioned why: calcium supplements create a temporary state of hypercalcemia that drives soft tissue calcification. They’re linked to increased heart disease risk. Dietary calcium, however, is less likely to overload your calcium disposal system.

Are you getting enough dietary calcium? To find out, log your meals for one to three days in the Cronometer app. You’ll get a good sense of your daily calcium intake.

If you need more calcium, eat more dairy, soft bones (best found in canned fish), and cruciferous vegetables. But you may not need more calcium. We analyzed thousands of people eating whole foods diets, and most of them were getting plenty.

That’s one reason we didn’t put calcium in LMNT, our electrolyte drink mix. On top of that, we had lingering concerns about calcium supplements, calcification, and heart health.

Before you get back to your day, I want to reinforce a point I’ve made several times throughout this article because it’s important: calcium intakes are mostly unrelated to serum calcium levels. Hypercalcemia and hypocalcemia are caused by other factors.

I hope this article helped clear up some key information about calcium for you!

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