Hypercalcemia is too much calcium in the blood.

Calcium is important to many body functions including:

• Bone formation
• Hormone release
• Muscle contraction
• Nerve and brain function

Parathyroid hormone (PTH) and vitamin D regulate calcium balance in the body. PTH is produced by the parathyroid glands -- four small glands located in the neck behind the thyroid gland. Vitamin D is obtained when the skin is exposed to sunlight, and from dietary sources such as:

• Egg yolks
• Fish
• Fortified cereals
• Fortified dairy products

Primary hyperparathyroidism is the most common cause of hypercalcemia and is due to excess PTH. This excess occurs due to an enlargement of one or more of the parathyroid glands.

Other medical conditions can also lead to hypercalcemia:

• Adrenal gland failure
• An inherited condition that affects the body's ability to regulate calcium (familial hypocalciuric hypercalcemia, FHH))
• A type of diuretic medication called thiazides
• Excess vitamin D (hypervitaminosis D) from diet or inflammatory diseases
• Hyperthyroidism
• Kidney failure
• Massive amounts of calcium in diet (milk-alkali syndrome)
• Not moving for long periods of time
• Some cancerous tumors (for example, lung cancers, breast cancer)

Hypercalcemia affects a very small percentage of the population. The widespread ability to measure blood calcium since the 1960s has improved detection of the condition, and today most patients with hypercalcemia have no symptoms.

Women over the age of 50 are most likely to have hypercalcemia, usually due to primary hyperparathyroidism.