A more general text about the lack of minerals can be found here.
Hypocalcemia (low blood calcium level) can be serious condition with many complications. Before mentioning its causes and symptoms, it is wise to have some information about calcium and its metabolism.
Calcium is an important element having many metabolic and structural functions. Its concentration in blood is approximately from 8.5-10.2 mg/dL (2.2-2.6 mmol/L). About half of this amount is free and half is bound to blood proteins. However, the greatest amount of calcium is located not in blood, but in the bones.
The blood concentration of calcium and its homeostasis is a complicated issue involving many factors. The calcium blood level is increased by parathyroid hormone and vitamin D and reduces by a hormone known as calcitonin. Parathyroid hormone is produced in the parathyroid glands, which are four small “balls” in the thyroid gland. Parathyroid hormone can increase serum calcium by increased disintegration of bone tissue and by increased production of vitamin D.
Vitamin D may be ingested with food, but the majority is produced by our own body. Vitamin D production is a complex process that takes place in kidneys, liver and skin. The whole process needs sunlight to be efficient. Vitamin D increases calcium absorption by the intestinal mucosa and somewhat inhibits its excretion by the kidneys.
The hormone calcitonin is also produced by parathyroid glands. It decreases calcium levels in the blood and thus works against the effect of parathyroid hormone.
Calcium level also depends on the function of kidneys (excretion of calcium into the urine), and the level of blood phosphate. Calcium and phosphate blood concentrations are in balance and that their product is constant. Elevation of blood phosphate decreases calcium level and vice versa.
Lowered production of parathyroid hormone by the parathyroid glands causes a decrease in blood calcium level. It can be caused by an autoimmune process, in which the immune system destroys cells of the parathyroid glands. Parathyroid glands may be damaged by accumulation of certain substances (iron in hemochromatosis, amyloid in amyloidosis, copper in Wilson's disease, etc.), by local tumors (especially thyroid gland tumors) or by local surgery. Rare inherited hypoparathyroidism may be a part of the so-called DiGeorge syndrome.
Vitamin D is very important for calcium metabolism as it increases calcium blood level by supporting its bowel absorption. Vitamin D is partly ingested and also produced in our body. The production is a complex process taking place in kidneys, liver and skin and it needs regular exposure to the sunlight.
Deteriorating kidneys are unable to excrete phosphate ions into the urine. As I have mentioned, the product of calcium and phosphate concentrations is constant and the increase of phosphate level therefore causes hypocalcemia. However, when this condition is prolonged, it leads to reactive increase of activity of PTH (secondary hyperparathyroidism) and the concentration of calcium in the blood begins to grow (so it is sometimes possible to find normal calcium level or even hypercalcemia).
Rapid and deep breathing (usually part of hysterical reaction) causes disturbance in internal environment resulting in decrease of free ionized blood calcium, which is bound to blood proteins (total calcemia does not change). This situation causes symptoms of hypocalcemia, especially tingling sensations of extremities, muscle cramps and convulsions.
Severe acute pancreatitis
Leaked pancreatic enzymes in severe acute pancreatitis cause metabolic change of body fat to fatty acids that precipitate with calcium ions by forming calcium salts, thus lowering calcium concentration.
Bone metastases are usually related to hypercalcemia as the majority of tumors destroy the bone tissue and release calcium (osteolytic process). However, some tumors are osteoblastic, i.e. their metastases may cause local overproduction of bone tissue. Such behavior is typical for prostate cancer. Such condition may be thus related to hypocalcemia.
Some medications used to treat excessive bone decalcification (such as bisphosphonates) may decrease blood calcium as its ions are built-in into the bones due to the drug effect.
Hypocalcemia affects many body systems reflecting the complex effect of calcium ion. Neuromuscular transmission is disrupted resulting in increased irritability of the muscles – increased deep tendon reflexes, more frequent muscle cramps and convulsions. Cardiac muscle is affected as well. Hypocalcemia can cause many types of arrhythmia including risk of a cardiac arrest. Digestive tract has increased peristalsis causing diarrhea. In the elderly, chronic hypocalcemia may be related to symptoms of dementia and confusion. When hypocalcemia is accompanied with a total deficiency of calcium in the body, the patient may suffer from osteoporosis.
The level of blood calcium can be easily evaluated from a venous blood sample. When the concentration is abnormal, it is advisable to know concentrations of parathyroid hormone and vitamin D and the renal parameters. Parathyroid glands may be checked by ultrasound, bone density by so-called densitometry and bone metastases by scintigraphy.
Hypocalcemia can be treated by calcium supplementation (oral forms, intravenous forms). When we administer chronic doses of calcium as tablets, it is wise to combine it with vitamin D supplements to improve calcium absorption in the guts. Of course, the underlying cause of hypocalcemia must be treated as well, if possible.