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Calcium 101: Testing, Top Foods, & Supplements

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Calcium 101: Testing, Top Foods, & Supplements

Calcium is the most bountiful mineral found in the human body. Although it's most known for its importance to the skeletal system, it's also used by many other body systems, including the nervous and cardiac systems. However, it's estimated that 39% of the population, including 49% of children, are not getting sufficient amounts of calcium. This article will discuss what calcium is, including its role in the body, how to check calcium levels, and good sources of calcium. 


What is Calcium?

Calcium is the fifth most common metal found in the earth's crust. Calcium is often found bound to other minerals, including calcium carbonate (limestone), calcium fluoride (fluorite), calcium sulfate (gypsum), and calcium chloro- or fluoro-phosphate (apatite). Calcium is essential for animals and plants. 

While 1% of the calcium in the body is in the blood and soft tissue, 99% is found in the bones and teeth. 

What is Calcium's Role in The Body?

Calcium levels in the body are tightly controlled by the parathyroid gland and thyroid gland. When calcium levels drop below a certain threshold, the parathyroid gland releases Parathyroid Hormone (PTH). PTH causes the kidneys to activate Vitamin D, which in turn will lower the amount of calcium being put into the urine. PTH, as well as excessive levels of vitamin D, can cause bones to leach calcium in order to raise serum levels, a process called bone resorption. Excessive levels of vitamin D will also cause increased intestinal absorption of calcium. When calcium levels are high in the blood, the thyroid gland releases the hormone calcitonin. Calcitonin inhibits the secretion of PTH, lowers intestinal absorption of calcium and bone resorption, and increases the secretion of calcium in the urine. 

Calcium is a major component of hydroxyapatite, the primary component of bones. As discussed above, calcium levels in the body can cause fluctuations in the amount of calcium in the bones and thus affect the bones' integrity. Hydroxyapatite is also found in the enamel of teeth. 

Calcium is also found in nerve and muscle cells. These cells contain calcium channels that can send electrical impulses that initiate muscular contractions, nerve impulses, constriction and relaxation of blood vessels, and release of certain hormones. 

Calcium also plays a large role in blood clotting, as calcium is required for proteins involved in the clotting cascade. 

How to Test Calcium Levels

Calcium levels can be checked in the blood. This test is often run when assessing conditions of the bones, kidney, liver, thyroid, parathyroid, pancreas, heart, nervous, and gastrointestinal systems. It's also often checked in cancer patients. Serum testing in the blood, such as the test offered by Access Medical Laboratories, assesses levels of calcium in the blood at the time of the blood draw and includes calcium that is both free and bound to other molecules, such as transfer proteins. This is also called "total calcium." Serum levels range from 8.5 to 10.5 milligrams (mg) per deciliter (dL). Ionized calcium tests, such as the test offered by Access Medical Laboratories, show only the level of free calcium in the blood. Ionized calcium levels range from 4.65 to 5.2 mg/dL. 

Calcium can also be measured in the urine to aid in the diagnosis of kidney stones and parathyroid conditions. The urinary calcium test, such as the 24-hour collection test offered by Access Medical Laboratories, has a normal range of 100 to 300 mg/dL. 

Calcium can also be found as a part of different testing panels. Mosaic Diagnostics offers a Calcium + Magnesium Profile urine test. Many labs offer comprehensive metabolic panels (CMPs), such as the CMP by BostonHeart Diagnostics, that includes kidney, liver, and blood sugar markers, as well as calcium and other markers. Lastly, micronutrient tests, such as the Micronutrient Test by SpectraCell Laboratories, assess numerous vitamins and minerals, including calcium.

Hypocalcemia, or calcium deficiency, is defined as a serum calcium level of less than 8.5 mg/dL. Postmenopausal women and those that avoid dairy are most at risk for hypocalcemia. Causes of hypocalcemia include vitamin D deficiency, magnesium deficiency, hypoparathyroidism, impaired absorption of calcium in the bones, illness, and certain medications. Common symptoms include muscle spasms and numbness around the mouth. Severe hypocalcemia can lead to brain and kidney calcifications, osteoporosis, cataracts, congestive heart failure, numbness and tingling, neurological conditions such as bipolar and depression, seizures, and coma. 

Hypocalcemia can also cause rickets and osteomalacia, although a vitamin D deficiency is usually concurrent. Children with rickets have skeletal malformations as a result of improper growth cartilage mineralization. Osteomalacia is characterized by improper bone mineralization that leads to soft bones. For both rickets and osteomalacia, the more severe the vitamin D deficiency, the higher calcium is required to prevent the progression of these diseases. 

Hypercalcemia, or excessive calcium, is defined as a serum calcium level higher than 10.5 mg/dL. When urinary levels are higher than 250 mg/dL in men and 200 mg/dL in women, this is referred to as hypercalciuria or high calcium in the urine. Both conditions can be a result of hyperparathyroidism, cancer, excessive vitamin D intake, and other conditions. Symptoms include fatigue, nausea, weight loss, constipation, increased urination, poor muscle tone, renal insufficiency, and heart arrhythmias. Hypercalcemia and hypercalciuria also increase the risk of cardiovascular disease mortality. 

It's important to note that calcium can interact with certain medications. Calcium taken around the same time as Levothyroxine, a common medication for hypothyroidism, Dolutegravir, an HIV medication, and quinolone antibiotics, can interfere with the absorption of these medications, making them less active. Lithium, a medication prescribed for bipolar disorder, can lead to hypercalcemia. Taking calcium with lithium can increase this risk.

How to Make Sure You Are Getting Enough Calcium in Your Diet 

The National Academies of Science, Engineering, and Medicine put together a Food and Nutrition Board that is responsible for formulating intake recommendations for vitamins and minerals. One of their recommendations is the Recommended Dietary Allowance (RDA), defined as the average daily amount of a vitamin or mineral that is needed to meet nutritional standards in most healthy individuals. 

Pregnant and lactating women's nutritional needs often differ from the general population; however, for calcium, they are the same as non-pregnant women, with RDA of 14-18 year-olds set at 1,300 mg and 19-50-year-olds at 1,000 mg for both pregnancy and lactation. 

When there is insufficient research to formulate an RDA, an Adequate Intake (AI) is formed. AIs are defined as levels assumed to reach nutritional requirements for a given population. The calcium AI for newborns to six months is 200 mg, and for seven to 12 months is 260 mg for both males and females. 

Calcium in the diet can come from food and supplements. 


Any food that contains 20% or more of the daily value of a given vitamin or mineral is considered to be a high source. In foods with varying amounts of fat, such as dairy products, the calcium content will change depending on the amount of fat. The higher the fat, the lower the calcium content.  


It's estimated that 22% of men and 32% of women take a calcium supplement. For children, 4-8% are taking a calcium supplement. It is rare to find a supplement that contains 100% daily value of calcium as calcium is bulky and would result in a rather large pill.  

There are many types of calcium, including calcium carbonate, calcium gluconate, calcium citrate, and calcium citrate malate. Many supplements include calcium carbonate, as it is the cheapest to make. However, it is also the most likely to lead to constipation. Most calcium supplements should be taken with food for better absorption. Although calcium citrate and calcium citrate malate can be taken on an empty stomach and are the preferred options for individuals with low stomach acid (hypochlorhydria).



As one of the most utilized minerals in the body, calcium plays an essential role in healthy functioning. Testing calcium levels is often done due to calcium's various roles throughout the body. It's imperative to ensure proper calcium levels in the diet, as too little or too much calcium can cause issues. Additionally, care should be taken when supplementing with calcium to avoid excess levels. 

The information provided is not intended to be a substitute for professional medical advice. Always consult with your doctor or other qualified healthcare provider before taking any dietary supplement or making any changes to your diet or exercise routine.
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