Studies suggest that calcium deficiency is much more common today than most people realize. Hypocalcemia, or low blood calcium, can trigger a wide range of symptoms, including muscle aches, irregular heartbeat, and fatigue. But what causes hypocalcemia in the first place? Read on to find out.
What is Hypocalcemia?
Hypocalcemia is when you have low blood calcium levels (“hypo” = low, “calcemia” = calcium in the blood). This condition can be either transient/acute or chronic.
You may or may not experience symptoms, depending on the severity of your deficiency. Symptoms can range from barely-noticeable and mild to serious and life-threatening complications. Hypocalcemia can even lead to death if left untreated .
This is unsurprising given that calcium is the most abundant mineral in the human body. Every cell in your body needs it to function. Calcium supports your bones, heart, muscles, and nervous system. But only around 1% of your total body calcium is found in the blood. The remaining 99% is stored in your bones and teeth .
Slightly lower calcium levels will generally not cause any symptoms.
- Muscle cramps
- Tingling in the hands and feet
- Irregular heartbeat
- Dry skin
- Tooth decay
The normal range for calcium levels in adults is around 8.5 to 10.5 mg/dL. These values can vary slightly from lab to lab. Hypocalcemia is defined as total blood calcium under 8.5 mg/dL. If calcium blood levels drop under 7 mg/dL, hypocalcemia is considered severe [5, 6, 7].
Causes shown below are commonly associated with low calcium levels. Work with your doctor or another health care professional to get an accurate diagnosis. Your doctor will interpret your result, taking into account your medical history, symptoms, and other test results.
1) Vitamin D Deficiency
If you don’t get enough vitamin D (from sun or supplements), you can develop hypocalcemia. This is because vitamin D helps absorb calcium in the gut. Vitamin D deficiency is the most common cause of hypocalcemia in primary care. It is estimated that up to 50% of the population may be deficient in vitamin D, so make sure you are getting enough [10, 11, 12].
2) Hypoparathyroidism (Low PTH)
Calcium blood levels are tightly 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 .
PTH raises blood calcium levels by increasing the absorption of calcium from the gut and kidneys. This hormone can also mobilize 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 known as bone resorption .
If PTH levels drop too low, so does calcium.
- Damage to the parathyroid glands (e.g. from surgery, radiation)
- Autoimmune disorders
- Genetic disorders
It is also possible to have normal levels of PTH but experience the symptoms of low PTH. This condition is known as pseudohypoparathyroidism and happens when cells stop responding to PTH as they should .
3) Not Getting Enough Calcium
This one is perhaps obvious and self-explanatory. But a large study from 2007 showed that most Americans are not getting the calcium they need .
People who are lactose intolerant, for example, or have eating disorders are at a higher risk of being calcium deficient 
Take a look at the recommended daily intake (RDA) of calcium below, and make sure you’re getting enough. If you can’t get enough from your diet, discuss calcium supplements with your doctor.
Be aware that certain substances in your diet can reduce absorption, or increase calcium loss. These include :
- Antinutrients (phytic acid, oxalic acid) that bind calcium in the gut
- Alcohol, which reduces calcium absorption and limits vitamin D production
- Caffeine, since it reduces absorption and increases calcium loss
If you follow a vegan diet, you might be at a higher risk of certain nutrient deficiencies, including calcium and vitamin D. A carefully-planned vegan diet can be healthy and nutritious. Eat more vegetables high in calcium but low in oxalic acid, which inhibits calcium absorption. Good sources of calcium include [19, 20, 21]:
- Tofu (calcium-set is best)
- Kale, broccoli, sprouts, cauliflower, bok choy, collard greens
Some foods – such as fruit juices, soy or nut milk – are fortified with calcium.
If you follow a paleo-style or carnivore diet, you are probably avoiding dairy, soy, and nuts. This leaves you with fewer calcium rich-options. Good calcium sources for people on meat-heavy diets include [19, 22]:
- Canned or fresh fish with bones (sardines, sardelles, or even salmon)
- Beef tripe
Those on a more liberal paleo diet have additional sources to choose from, including kale, broccoli, bok choy, and other leafy greens.
Recommended Dietary Allowances (RDA) for Calcium
Below is the RDA for calcium. You should aim to get enough calcium every day, either from food or supplements. Going below the RDA for a short while is unlikely to cause harm, but it can lead to health problems in the long run .
|0–6 months*||200 mg||200 mg|
|7–12 months*||260 mg||260 mg|
|1–3 years||700 mg||700 mg|
|4–8 years||1,000 mg||1,000 mg|
|9–13 years||1,300 mg||1,300 mg|
|14–18 years||1,300 mg||1,300 mg||1,300 mg||1,300 mg|
|19–50 years||1,000 mg||1,000 mg||1,000 mg||1,000 mg|
|51–70 years||1,000 mg||1,200 mg|
|71+ years||1,200 mg||1,200 mg|
IMPORTANT: Not getting enough calcium in your diet may not show on your blood test. That’s because the bones will release more calcium into the blood to compensate. Testing bone mineral density and PTH levels, instead, can tell your doctor more about your calcium status.
4) Gut Disorders
Disorders and diseases that compromise calcium absorption in the gut can also lead to hypocalcemia. Examples include chronic diarrhea and inflammatory bowel diseases such as Chrons and ulcerative colitis [23, 10].
5) Abnormal Magnesium Levels
Magnesium deficiency is another factor that can lead to hypocalcemia. Without sufficient levels of magnesium, parathyroid hormone (PTH) cannot function properly. Magnesium is important for both the production and secretion of PTH [24, 25, 26].
On the other hand, a study suggests that high magnesium levels can also suppress PTH release, decreasing the calcium levels as a result .
6) High Phosphorus Levels
When phosphorus levels increase suddenly (e.g. in rhabdomyolysis or tumor lysis syndrome). Phosphorus binds calcium, decreasing active/ionized calcium levels .
7) Low Protein Levels
Low calcium levels are often caused by low protein levels, especially albumin. This is the case in :
- Liver disease
However, in these cases, the unbound (ionized) calcium remains normal. Therefore, your doctor can rule this out by checking your albumin or ionized calcium levels .
During menopause, the body’s production of PTH, estrogen and other hormones changes. Due to a decrease in estrogen production, women are less able to retain calcium from dietary sources. Bone turnover (breakdown and replacement) rapidly increases and hypocalcemia is more common. Women also have a higher risk of osteoporosis after menopause [27, 28].
9) Kidney Disease
Kidney disease causes hypocalcemia since damaged kidneys retain less calcium and let more of it slip out into the urine. Damaged kidneys also produce less active vitamin D, which causes less calcium to be absorbed in the gut. Meanwhile, rising phosphate levels increase bound calcium and its flushing with the urine [10, 29].
Pancreatitis or pancreas inflammation is often accompanied by hypocalcemia, but the exact reason is unknown .
One theory is that lipopolysaccharides (LPS), toxins released from bacteria, end up in the bloodstream when the gut barrier is compromised. LPS cause calcium to accumulate in cells and tissues, leading to a drop in blood calcium levels .
11) Certain Drugs
Certain medications may cause (or contribute to) hypocalcemia. These include:
- Bisphosphonates used to treat osteoporosis 
- Anticonvulsants [33, 32]
- Glucocorticoids, used to suppress inflammation 
- Proton pump inhibitors, used to decrease stomach acid [32, 24]
- Laxatives 
12) Genetic Disorders
Irregular Calcium Levels?
Chronic or severe hypocalcemia should always be treated by a doctor. There may be serious underlying medical conditions that can have dangerous consequences and require immediate treatment.
Vitamin D deficiency, low parathyroid gland function, gut disorders, and kidney disease are among the more common causes of hypocalcemia. Rarely, you can become deficient if you’re not getting enough dietary calcium. Work with your doctor if your calcium levels are low to discover and treat the underlying cause.