By Cat Troiano
Calcium is one of the seven macrominerals found in the human body. All minerals are crucial for carrying out a variety of functions to sustain human life. Calcium is not produced in the body, and so this important micronutrient must be consumed through diet. Calcium is the building block for bone and tooth formation. Bones contain 99 percent of the body’s calcium. The remaining small percentage carries out additional critical functions, including:
- Works together with vitamin K to aid in blood coagulation
- Regulates heartbeat rhythms
- Enables vasoconstriction and vasodilation to stabilize blood pressure
- Maintains permeability and stability of cell membranes to enable cellular communication
- Aids in neurotransmission
- Enables the binding of muscle fiber proteins to facilitate muscle contraction
That’s a lot of jobs for only one percent! If there is an insufficient amount of calcium on board to carry out these vital roles, then the parathyroid glands come to the rescue. These four glands that neighbor the thyroid gland release an increased amount of parathyroid hormone (PTH) when low blood calcium levels are detected, prompting the bones to release calcium into the blood. PTH also stimulates the production of calcitriol, an inactive form of vitamin D, to facilitate increased dietary calcium absorption in the gastrointestinal tract. PTH also acts on the kidneys to prevent the filtration of calcium for elimination and instead encourage reabsorption of calcium back into the blood.
Conversely, when blood calcium levels are too high, the parathyroid gland produces a lower amount of PTH, and the thyroid gland kicks in to release calcitonin, a hormone that reduces blood calcium levels by reducing the breakdown of bone. Throughout life, bone continuously breaks down and rebuilds, a normal process called remodeling. The human skeleton is almost entirely rebuilt over the course of every 10 years. Remodeling enables the removal of calcium from bone when blood calcium levels are deficient or when the need for increased blood calcium arises, such as during pregnancy and lactation. PTH stimulates specialized bone cells called osteoblasts to build bone tissue. PTH, as well as calcitonin, can also inhibit osteoclasts, the bone cells that break down bone tissue.
Maintaining an ideal calcium level for optimal physiological function is a balancing act that the body must perform. Testing blood calcium levels is essential so that abnormal levels can be addressed to restore proper function.
There are two presentations of calcium in the blood. Free calcium, also called ionized calcium, is calcium which is not bound to organic molecules. Bound calcium is that which is bound to molecules, predominantly to the protein albumin and, in smaller proportions, to immunoglobulins and to phosphorus.
The body’s ability to utilize a mineral depends on the mineral’s bioavailability. Once a mineral is bound, it is no longer bioavailable. Free calcium is the more active form of calcium with a higher bioavailability, and bound calcium accounts for roughly 40 percent of blood calcium. Therefore, total calcium is considered to be a mineral that is of medium bioavailability.
Tests that evaluate blood calcium levels include the following:
Total calcium test – evaluates levels of both free and bound calcium. The normal reference range for an adult is a total blood calcium level of 8.5 to 10.3 mg/dL.
Ioniozed calcium test– evaluates the blood calcium level of free calcium only. The normal reference range for an adult is an ionized calcium level greater than 4.6 mg/dL.
Total calcium levels are also typically included in both the comprehensive metabolic panel and the basic metabolic panel.
When the body has an excess surplus of calcium, some of that excess is eliminated through urination. The urinary Ca+2 test evaluates the amount of calcium that has been passed in all of a patient’s urine that has been excreted over 24 hours. The normal reference range for urinary Ca+2 is 100 to 300 mg per 24 hours.
Fasting is not necessary for calcium level testing, but patients should be instructed to refrain from taking any medications or supplements that can affect calcium levels, including anticonvulsant drugs, diuretics, bisphosphonates, corticosteroids, lithium, estrogen, calcium supplements and vitamin D supplements.
Patients for whom calcium level testing should be ordered include those with:
- Kidney disease
- Thyroid disease
- Neurological deficits
- Liver disease
- Abnormal EKG
Ionized calcium levels should be monitored in patients who have cancer, who are critically ill and receiving intravenous fluid therapy, who are receiving blood transfusions and who have abnormal albumin levels on their metabolic panels.
What Does a Low Calcium Level Indicate?
Hypocalcemia is defined as an abnormally low calcium level. This can result when too much calcium is eliminated through urination or when an insufficient amount of calcium is released from bone into the blood. Causes of hypocalcemia include the following:
- Underactive parathyroid gland
- Low blood protein levels
- Low magnesium levels
- Low vitamin D level
- High phosphorus level
- Kidney failure
- Dietary calcium deficiency
- Use of certain drugs, including bisphosphonates, corticosteroids, calcitonin, anticonvulsants, such as phenobarbitol, and certain antibiotics, such as plicamysin and rifampin
- Dietary calcium deficiency
Initially, patients with moderately low calcium levels may be asymptomatic. Severely low or prolonged low calcium levels can result in symptoms that include arrhythmias, tingling in the hands or feet, muscle spasms, muscle cramping, confusion, memory loss, hallucinations and seizure activity.
Hypocalcemia can usually be corrected with the use of calcium supplements, and vitamin D supplementation may be recommended as well. Treatment for the underlying cause of low calcium levels must also be recommended.
What Does an Elevated Calcium Level Indicate?
Hypercalcemia, the opposite of hypocalcemia, is defined as an abnormally high calcium level. Causes of hypercalcemia include the following:
- Overactive parathyroid glands
- Cancer, including lung cancer, breast cancer, blood cancers and cancers that have metastasized to the bones
- Paget disease
- Certain drugs, including lithium prescribed for the treatment of bipolar disorder, diuretics prescribed for the treatment of hypertension and heart failure, and antacids
- Excessive intake of calcium and/or vitamin D supplements over an extended duration
- Extreme dehydration
- Patient inactivity
As in the case of hypocalcemia, mild hypercalcemia may present no apparent symptoms. Patients with more severe or advanced cases of hypercalcemia experience increases in water intake and urinary output, kidney stones, nausea, vomiting, constipation, abdominal pain, decreased appetite, bone pain, muscle weakness, fatigue, depression, syncope, arrhythmia and coma.
Drug therapy is typically the course of treatment for hypercalcemia. The drugs that are prescribed are dependent on the cause of the high calcium levels. Commonly used drugs include biphosphonates, calcitonin and corticosteroids.
Depending on the abnormal calcium level test result, additional screenings may be ordered, such as thoracic diagnostic imaging, thyroid and parathyroid hormone levels, phosphorus level, vitamin D level and a renal function panel.
How Much Calcium Should Be Taken In?
Since calcium must be consumed, patients should be educated as to how much calcium they should be taking in. Female patients are especially concerned, knowing that as their age advances and their estrogen hormone levels decline sharply during menopause, the body’s bone formation capability is less able to keep up with the breaking down of bone, resulting in lower bone mass density. This condition, known as osteoporosis, results in brittle bones than fracture easily and can render a patient physically impaired, threatening their independence and quality of life.
According to the National Osteoporosis Foundation, healthy adults should strive to take in 1,000 mg of calcium daily. That amount should be increased to 1,200 mg daily for women older than 50 and for men older than 70 years of age. Foods that contain calcium include, but are not limited to, milk, yogurt, cheese, egg yolks, almonds, soybeans, edamame, tofu, sardines and leafy greens, such as spinach, kale and bok choy.
Remember that calcium cannot be absorbed without the help of vitamin D. Only three vitamins can be produced by the human body, and although vitamin D is one of the three, in addition to vitamin K and biotin, it is only produced when a patient’s skin receives adequate sunlight exposure. Healthy adults should take in 5µg of vitamin D daily. Wild-caught tuna and salmon are among the few foods that naturally contain vitamin D, but many cereals, dairy products and orange juices are fortified with vitamin D and, in some cases, with calcium as well.
As described above, you can have too much of a good thing. All patients should have their calcium levels checked and their overall metabolic health evaluated prior to consulting with their physicians about calcium supplementation.