Calcium is the most abundant mineral in your body with 99 percent of it contained in your bones and teeth, according to the Linus Pauling Institute at Oregon State University. The remainder of your calcium is found in other tissues and in your extracellular fluids, where its concentration is tightly controlled by your parathyroid glands, your kidneys and vitamin D levels. If your serum calcium rises beyond a relatively narrow range, it interferes with the proper function of your muscles, nervous system and heart.
Functions
In addition to adding strength and form to your skeleton, calcium performs a variety of metabolic tasks in your body. Through its interactions with a molecule called calmodulin, calcium regulates a wide array of cellular processes. A 2007 review in "Subcellular Biochemistry" cites calcium's roles in hormone secretion, energy metabolism, nervous system development and immune function. Due to the calcium ion's electrical properties, it is an essential participant in nerve impulse generation, muscle contraction and heart activity. Excess calcium in your extracellular fluids can disrupt these important functions.
Action Potentials
In order for your heart and other electrical tissues to function normally, their cell membranes must be capable of regulating the to-and-fro movement of electrically charged ions. This flux of ions generates a current -- an "action potential" -- which is propagated through the organ or tissue. In your heart, synchronized action potentials generated by the movement of calcium into cardiac muscle cells permits the regular contractions that constitute your heartbeat. When there is too much calcium in the fluids surrounding your cells -- a condition called hypercalcemia -- the activity of your heart and other electrical tissues is impaired.
Hypercalcemia
Several conditions, including hyperparathyroidism, vitamin D toxicity, prolonged immobilization and cancer, can cause hypercalcemia. According to "The Merck Manual of Diagnosis and Therapy," the underlying cause of hypercalcemia in most of these conditions is excessive bone turnover. Mild hypercalcemia -- serum calcium levels between 10.5 and 11.5 mg/dL -- may be asymptomatic. Levels over 12 mg/dL can cause emotional problems, confusion, delirium and muscle weakness. A case report in the August 2005 issue of "Heart" demonstrates that severe hypercalcemia -- in the 16 to 17 mg/dL range -- can cause chest pain and ECG changes which mimic a heart attack. Hypercalcemia can lead to the development of abnormal heart rhythms, particularly if you have heart disease or take digoxin. Calcium levels above 18 mg/dL cause shock, kidney failure, coma, cardiac arrest and death.
Considerations
Hypercalcemia does not result from over-absorption of calcium from foods, but it can occur with the overuse of calcium supplements and from several medical conditions. The Linus Pauling Institute cites the use of large doses of calcium -- 1.5 to 16.5 g daily -- in conjunction with antacid therapy as a cause of hypercalcemia. Heart function is adversely affected by hypercalcemia. Recommended dietary allowances for calcium vary from 200 mg daily for infants to 1,300 mg for pregnant women. Ask your physician about the best calcium dosage for you.
References
- Linus Pauling Institute at Oregon State University: Calcium"
- "Subcellular Biochemistry"; Physiological Roles of the Ca2+/CaM-Dependent Protein Kinase Cascade in Health and Disease; J. Colomer, A.R. Means; 2007
- "Heart"; ST Segment Elevation Mimicking Acute Myocardial Infarction in Hypercalcemia; S. Turhan, et al.; August 2005
