Calcium

What Is Calcium?

Calcium is the most abundant mineral in your body — and most people know it for building strong bones and teeth. But calcium does far more than that. It helps your muscles contract, your blood clot when you get a cut, your nerves send signals, and your heart beat in a regular rhythm. In fact, your body considers keeping blood calcium levels steady so important that it has an elaborate system of hormones dedicated to the job.

About 99 percent of your calcium lives in your bones and teeth, serving as both structural support and a storage bank. The remaining 1 percent circulates in your blood and other body fluids, where it carries out those critical daily functions. When blood calcium starts to dip, your body pulls calcium out of your bones to make up the difference.

What Does It Measure?

A calcium blood test typically measures the total amount of calcium in your blood. This includes calcium that is attached to proteins (mainly albumin) and calcium that is floating free. The "free" form — called ionized calcium — is the portion that is biologically active and doing the actual work.

Because total calcium is influenced by your albumin level, your doctor may calculate a "corrected calcium" if your albumin is abnormally low or high. In some situations, your doctor may order an ionized calcium test directly, which measures only the active form and is not affected by protein levels.

Normal Ranges

| Group | Range | Unit | |---|---|---| | Adults (total calcium) | 8.5 – 10.5 mg/dL | mg/dL | | Adults (ionized calcium) | 4.6 – 5.3 mg/dL | mg/dL | | Children (total calcium) | 8.8 – 10.8 mg/dL | mg/dL | | Newborns | 8.0 – 10.5 mg/dL | mg/dL | | Pregnant individuals | 8.2 – 9.7 mg/dL | mg/dL | | Critical low | Below 7.0 mg/dL | mg/dL | | Critical high | Above 12.0 mg/dL | mg/dL |

Note: Some labs report results in mmol/L. To convert mg/dL to mmol/L, divide by 4. For example, 10.0 mg/dL equals 2.5 mmol/L.

What Does a High Level Mean?

High blood calcium (hypercalcemia) means there is more calcium floating in your bloodstream than your body needs. Mild elevations are surprisingly common and sometimes found incidentally on routine blood work.

Possible causes of high calcium:

• Primary hyperparathyroidism — the most common cause, where one or more parathyroid glands become overactive and release too much parathyroid hormone (PTH), pulling calcium out of bones
• Cancer, particularly lung cancer, breast cancer, or blood cancers like multiple myeloma, which can release substances that raise calcium
• Excessive vitamin D supplementation
• Certain medications, including thiazide diuretics and lithium
• Prolonged immobility or bed rest, which causes bone to release calcium
• Sarcoidosis and other granulomatous diseases
• Overactive thyroid (hyperthyroidism)

Common symptoms of high calcium:

• Excessive thirst and frequent urination
• Nausea, vomiting, or constipation
• Fatigue and weakness
• Confusion or difficulty thinking
• Bone pain
• Kidney stones
• Abdominal pain

Recommended next steps:

• Your doctor will likely order a parathyroid hormone (PTH) test to help pinpoint the cause
• Vitamin D, phosphorus, and kidney function tests are also commonly checked
• If hyperparathyroidism is confirmed, you may be referred to an endocrinologist
• Stay well hydrated — drinking plenty of water helps your kidneys flush out excess calcium
• In severe cases, hospital treatment with IV fluids and medications may be needed

What Does a Low Level Mean?

Low blood calcium (hypocalcemia) means your body does not have enough calcium circulating to keep everything running smoothly. Because calcium is so crucial for muscles and nerves, low levels can cause noticeable and sometimes alarming symptoms.

Possible causes of low calcium:

• Low vitamin D levels (vitamin D is needed to absorb calcium from food)
• Hypoparathyroidism — the parathyroid glands do not produce enough PTH, which can happen after thyroid or neck surgery
• Chronic kidney disease, which reduces the kidneys' ability to activate vitamin D
• Magnesium deficiency, which can impair parathyroid hormone function
• Malabsorption conditions like celiac disease or inflammatory bowel disease
• Pancreatitis
• Certain medications, including bisphosphonates and some anti-seizure drugs
• Low albumin levels (which can make total calcium appear low even when ionized calcium is normal)

Common symptoms of low calcium:

• Tingling or numbness in the fingers, toes, or around the mouth
• Muscle cramps or spasms, especially in the hands and feet
• Fatigue
• Brittle nails and dry skin
• Confusion or memory problems
• Irregular heartbeat
• In severe cases, seizures

Recommended next steps:

• Your doctor will investigate the underlying cause — checking vitamin D, PTH, magnesium, and kidney function
• Calcium and vitamin D supplements are commonly recommended
• If albumin is low, your doctor may order an ionized calcium test to confirm true calcium status
• Severe hypocalcemia may require IV calcium in a hospital
• Recheck your calcium after treatment to confirm improvement

When Should You Get Tested?

Calcium is included in the basic metabolic panel (BMP) and comprehensive metabolic panel (CMP), which means it is often checked as part of routine blood work. You might want to specifically discuss your calcium level with your doctor if you:

• Have been diagnosed with osteoporosis or osteopenia
• Have kidney disease
• Have thyroid or parathyroid problems
• Experience frequent muscle cramps, tingling, or numbness
• Have a history of kidney stones
• Take calcium or vitamin D supplements and want to make sure your levels are appropriate
• Have a digestive condition that might affect calcium absorption
• Are going through menopause (calcium needs increase)

How to Improve Your Levels

Food sources: Dairy products like milk, yogurt, and cheese are the most well-known sources of calcium. But you can also find plenty in sardines (with bones), canned salmon, tofu made with calcium sulfate, fortified plant milks and juices, broccoli, kale, bok choy, and almonds. A cup of milk or yogurt provides roughly 300 mg of calcium.

Get enough vitamin D: Calcium and vitamin D go hand in hand. Without adequate vitamin D, your body cannot absorb calcium efficiently no matter how much you consume. Aim for 600 to 800 IU of vitamin D daily, or more if your levels are low.

Supplements: If you cannot get enough calcium from food, calcium citrate and calcium carbonate are the two main supplement forms. Calcium citrate is absorbed better on an empty stomach and is gentler for people with low stomach acid. Calcium carbonate is best taken with food. Spread your doses out — your body absorbs calcium best in amounts of 500 mg or less at a time.

Weight-bearing exercise: Activities like walking, jogging, dancing, and strength training help stimulate bone to hold onto calcium and stay strong.

Limit excess sodium and caffeine: High sodium intake and excessive caffeine can increase the amount of calcium your kidneys excrete.

Frequently Asked Questions

Q: Can I take too much calcium from supplements?

Yes. The upper limit for most adults is 2,500 mg per day from all sources (food plus supplements). Too much calcium can increase your risk of kidney stones and may contribute to cardiovascular problems. It is generally best to get as much calcium as possible from food and only supplement the gap.

Q: My calcium is slightly high — should I be worried?

Mildly elevated calcium (around 10.5 to 11.0 mg/dL) is often caused by primary hyperparathyroidism, which is usually a benign condition involving a small growth on one of the parathyroid glands. It is not an emergency, but it is worth following up with your doctor to confirm the cause and discuss whether monitoring or treatment is appropriate.

Q: Does calcium from plant-based foods absorb as well as calcium from dairy?

It depends on the food. Calcium from kale, broccoli, and bok choy actually absorbs quite well — in some cases better than dairy. However, calcium from spinach, Swiss chard, and rhubarb is poorly absorbed because these foods are high in oxalates, which bind to calcium and prevent your body from using it. Variety is your best strategy.

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This content is for educational purposes only and is not medical advice. Always consult your healthcare provider about your lab results.