Calcium imbalance

Calcium plays an indispensable role in cell permeability, formation of bones and teeth, blood coagulation, transmission of nerve impulses, and normal muscle contraction. Nearly all (99%) of the body’s calcium is found in the bones. The remaining 1% exists in ionized form in serum, and it’s the maintenance of the 1% of ionized calcium in the serum that’s critical to healthy neurologic function.

The parathyroid glands regulate ionized calcium and determine its resorption into bone, absorption from the GI mucosa, and excretion in urine and stool. Severe calcium imbalance requires emergency treatment because a deficiency (hypocalcemia) can lead to tetany and seizures; an excess (hypercalcemia), to cardiac arrhythmias and coma.

Causes

Several factors can cause calcium imbalance.

Hypocalcemia

Inadequate intake of calcium and vitamin D results in inhibited intestinal absorption of calcium.
Hypoparathyroidism as a result of injury, disease, or surgery decreases or eliminates secretion of parathyroid hormone (PTH), which is necessary for calcium absorption and normal serum calcium levels.
Malabsorption or loss of calcium from the GI tract can result from increased intestinal motility from severe diarrhea or laxative abuse. Malabsorption of calcium from the GI tract can also result from inadequate levels of vitamin D or PTH or a reduction in gastric acidity, which decreases the solubility of calcium salts.
Severe infections or burns can lead to diseased and burned tissue trapping calcium from the extracellular fluid.
Overcorrection of acidosis can lead to alkalosis, which causes decreased ionized calcium and induces symptoms of hypocalcemia.
Pancreatic insufficiency may cause malabsorption of calcium and subsequent calcium loss in stool. In pancreatitis, participation of calcium ions in saponification contributes to calcium loss.
Renal failure results in excessive excretion of calcium secondary to increased phosphate retention. Renal failure also results in loss of the active metabolite of vitamin D, which impairs calcium absorption.
Hypomagnesemia causes decreased PTH secretion and blocks the peripheral action of that hormone.

Hypercalcemia

Hyperparathyroidism increases serum calcium levels by promoting calcium absorption from the intestine, resorption
from bone, and reabsorption from the kidneys.
Hypervitaminosis D can promote increased absorption of calcium from the intestine.
Tumors raise serum calcium levels by destroying bone or by releasing PTH or a PTH-like substance, osteoclast-activating factor, prostaglandins and, perhaps, a vitamin D–like sterol.
Multiple fractures and prolonged immobilization release bone calcium and raise the serum calcium level.
Multiple myeloma promotes loss of calcium from bone.