Key takeaways:
Hypocalcemia is the medical term for low calcium levels in the blood. Some of the most common causes include problems with the parathyroid gland, low magnesium levels, and vitamin D deficiency.
A low calcium level doesn’t always cause symptoms at first. If the condition progresses, symptoms can include a tingling sensation around the mouth, muscle spasms, confusion, and breathing difficulties.
The amount of calcium in your blood isn’t a measure of your calcium intake. This is because when you’re not eating enough calcium, your body pulls calcium from your bones to keep your blood levels normal.
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Almost 99% of the calcium in your body is stored in your bones. The remaining 1% circulates in your blood. But that small amount has a big job to do. Calcium plays a critical role in nerve conduction, muscle contraction, and heart rate and blood pressure — even blood clotting. So, having a low calcium level can cause some serious problems.
A low calcium level isn’t a reflection of your daily calcium intake from food or supplements. That’s because your body has an elegant system to keep your calcium levels steady, no matter how much you’re eating. Here, we’ll explain why the system can go out of balance and cause calcium levels to drop — and what that means for you and your health.
What is hypocalcemia?
Hypocalcemia is the medical term for low calcium levels in the blood. These levels can be measured in two different ways — and we’ll explain why.
Some of the calcium that circulates in the blood is bound to other molecules — like proteins or minerals. Bound calcium is inactive and the body can’t use it. The calcium that's not bound is free and ready for action.
A blood test can measure:
Total calcium level: This is the amount of both bound and unbound calcium together. Anything below 8.5 mg/dL is considered low.
Ionized calcium: “Ionized” is another term for the unbound or free calcium. Anything below 4.65 mg/dL is considered low.
Hypocalcemia can be diagnosed with either measurement. But in some cases, the ionized calcium gives a more accurate picture of someone's calcium levels — since it's the form that's active and participating in bodily functions.
Before we move on, it's important to clarify that hypocalcemia isn’t the same thing as a calcium deficiency. Calcium deficiency means someone isn’t getting enough calcium from their diet. But as we’ll see in the next section, low calcium levels aren’t caused by calcium deficiency.
What causes hypocalcemia?
The body keeps calcium levels in the blood under tight control with parathyroid hormone (PTH). When your blood calcium levels start to drop, this hormone is released — and this triggers calcium to be released from your bones.
But a few other things also play a role in controlling your calcium levels, which we’ll see in the causes below.
The most common causes of hypocalcemia are:
Low levels of PTH: This usually happens after people have their parathyroid gland removed. It can also happen when the gland is damaged by another condition — like certain autoimmune diseases or surgery on the nearby thyroid.
Low magnesium levels: Magnesium plays an important role in PTH release and activity. So a magnesium deficiency can impair the body’s normal hormonal response to low calcium.
Low vitamin D levels: Your body needs vitamin D to absorb calcium from the gut. Vitamin D also helps release calcium from your bones when you need it. Vitamin D deficiency can be caused by things like low intake and low sunlight exposure.
High phosphate levels: Phosphate prevents PTH release. This is a less common cause of low calcium, but it can happen with kidney disease and other more rare conditions like rhabdomyolysis.
Chronic kidney disease: The kidneys help the body hold onto calcium when levels start to drop. They can also affect phosphate and vitamin D levels.
Pancreatitis: Low calcium often accompanies pancreatitis, an inflammation of the pancreas. Gallstones and heavy alcohol intake can lead to pancreatitis.
Medications: Common culprits include certain seizure medications, bisphosphonates, proton pump inhibitors (PPIs), and H2 blockers. Blood transfusions can also lead to low calcium levels.
Severe illness: Any type of critical illness — like sepsis or a major trauma — can cause low calcium through many different mechanisms. Low calcium has been seen in severe COVID-19 infections, for example.
What are the signs and symptoms of hypocalcemia?
It takes time for low calcium levels to cause symptoms, so it may go undetected in the early stages. The appearance of symptoms depends on how low calcium levels are and how quickly they drop.
If your calcium level decreases gradually over time, your body has a longer time to adjust and may produce fewer signs. Symptoms are more likely when your blood calcium level is below 7.5 mg/dL, or when it drops quickly.
Symptoms of low calcium include:
Tingling around the mouth
Numbness and tingling in hands and feet
Muscle cramps or spasms, especially in the hands and feet
Wheezing, throat spasms, or breathing issues
Difficulty swallowing
Mood symptoms like irritability or depression
Dry skin, thin hair, or brittle nails
Severe cases of low calcium can lead to life-threatening complications, like cardiac arrest or seizure. However, it's very rare for low calcium to be fatal.
How is hypocalcemia treated?
Treatment of hypocalcemia depends on how low your calcium level is and what’s causing it in the first place. The goal is to raise the calcium to a safe level and address the underlying cause.
Treatment for hypocalcemia may include:
Oral calcium: If symptoms are mild, low calcium is usually treated with oral supplements, like calcium carbonate or calcium citrate. Vitamin D is often added to help your body absorb the calcium.
IV calcium: For more serious symptoms — muscle spasms, tingling, or abnormal heart rhythms — IV calcium (usually calcium gluconate) may be needed. This treatment is given in a monitored setting.
Vitamin D and/or magnesium supplements: As mentioned above, vitamin D and magnesium play key roles in maintaining healthy calcium levels. So, if either one is low, supplements are often added as part of treatment.
PTH: When hypocalcemia is due to low levels of this hormone, treatment may include PTH replacement therapy.
Frequently asked questions
Low calcium isn’t usually a sign of cancer. In rare cases, certain cancers — like thyroid or colon cancer — can lead to low calcium levels. But, more often, cancer is linked to high calcium levels. If calcium is low in someone with cancer, it’s often due to treatments like chemotherapy or certain medications, rather than the cancer itself.
Most adults (over age 19) need 1,000 mg of calcium per day. This increases with age:
Females over age 50 need 1,200 mg per day.
Males over age 70 need 1,200 mg per day.
Remember that low calcium levels in the blood aren’t an indicator of dietary intake of calcium. So it's very important to make sure you're getting enough calcium per day. Over time, dietary calcium deficiency can lead to osteoporosis.
Dairy foods — such as milk, cheese, and yogurt — are the best sources of calcium. If you don’t consume dairy, you can choose other calcium-rich foods, such as salmon, leafy greens, and tofu (made with calcium sulfate).
Low calcium isn’t usually a sign of cancer. In rare cases, certain cancers — like thyroid or colon cancer — can lead to low calcium levels. But, more often, cancer is linked to high calcium levels. If calcium is low in someone with cancer, it’s often due to treatments like chemotherapy or certain medications, rather than the cancer itself.
Most adults (over age 19) need 1,000 mg of calcium per day. This increases with age:
Females over age 50 need 1,200 mg per day.
Males over age 70 need 1,200 mg per day.
Remember that low calcium levels in the blood aren’t an indicator of dietary intake of calcium. So it's very important to make sure you're getting enough calcium per day. Over time, dietary calcium deficiency can lead to osteoporosis.
Dairy foods — such as milk, cheese, and yogurt — are the best sources of calcium. If you don’t consume dairy, you can choose other calcium-rich foods, such as salmon, leafy greens, and tofu (made with calcium sulfate).
The bottom line
Hypocalcemia — or low calcium levels in the blood — is a relatively rare condition. The most common cause is low levels of parathyroid hormone (PTH), usually after the parathyroid gland has been surgically removed. Other causes can include low magnesium, low vitamin D, and chronic kidney disease.
Since low calcium levels aren’t related to dietary intake of calcium, getting a blood test for calcium can’t diagnose calcium deficiency. If you're concerned about your calcium intake or bone health, talk to your primary care provider about your concerns and possible testing.
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References
Anastasopoulou, c., et al. (2026). Hypocalcemia. StatPearls.
Duval, M., et al. (2018). Is severe hypocalcemia immediately life threatening? Endocrine Connections.
Ferraz Gonçalves, J. A., et al. (2019). Hypocalcemia in cancer patients: An exploratory study. Porto Biomedical Journal.
