Calcium is well know as the main component of bone but it has a host of different functions in the body. Whle 99% of the calcium in the human body is within the bones, the other 1% is found outside of the bones where it has important functions particularly for muscle and nerve function. Therefore the body maintains certain levels of calcium in the bloodstream where it can be rapidly transported to cells that require it.
What is hypocalcemia?
Hypocalcemia is the medical term for low calcium levels in the blood. It specifically refers to a total serum calcium concentration less than 8.8 mg/dL (2.20 mmol/L) or a serum ionized calcium concentration less than 4.7 mg/dL (1.17 mmol/L). Most of the time there are no signs and symptoms indicative of low blood calcium levels and it can only be ascertained with diagnostic investigations.
The body is constantly managing the calcium levels in the bones, cells, tissue fluid and blood. Hypocalcemia can affect children or adults but often for different reasons. In children, low blood calcium levels are more likely to be caused by nutritional deficiencies, wheras in adults it is more likely due to kidney diseases that causes loss of calcium in the urine. Vitamin D deficiency can affect all ages.
Calcium in the Blood
Calcium is an essential mineral that is needed throughout the body. Most calcium is used for structures like the bones but it is also important for the functioning of muscles, nerves and both inside and outside other cells for various different processes. Some of this calcium outside of the bones is also found in the bloodstream in three different forms:
- Ionized calcium which is unbound. This accounts for 50% of blood calcium.
- Protein-bound calcium, specifically to albumin. This accounts for 40% of blood calcium.
- Anion-bound calcium (bound to phosphate, carbonate, citrate, lactate, sulfate). This accounts for 10% of blood calcium.
It is this ionized calcium that has active functions in the body. Protein-bound calcium acts as a reserve for calcium which can be transported and released where needed. The body is constantly balancing the amount of calcium within bones, cells and the bloodstream. Calcium is therefore needed on a constant basis and it is sourced through various foods such as dairy, meat, dried beans, nuts and leafy vegetables.
Read more on calcium in foods.
Signs and Symptoms
Mild hypocalcemia that is acute may present with little to no symptoms. However, as the condition worsens or persists for prolonged periods then there may be symptoms mainly of muscle and nerve dysfuction. This may include:
- Muscle cramps and twitching
- Paresthesia – tingling and numbness
- Encephalopathy – confusion, depression, hallucinations
- Tetany – muscle spasms and stiffness
- Difficulty speaking and voice changes
- Arrhythmia – abnormal heart rate
Symptoms like dry skin, brittle nails and coarse hair may arise in chronic hypocalcemia.
Causes of Low Blood Calcium Levels
Low blood calcium levels may be an indication of loss of calcium mainly through urine output, inadequate absorption of calcium or when insufficient calcium is moved into the bloodstream. Calcium levels are closely linked to the levels of other substances like magnesium and phosphate. Therefore the cause of hypomagnesemia (low blodo magnesium) and hyperphosphatemia (high blood phosphates) need to be considered in hypocalcemia.
The parathyroid gland plays a critical role in managing calcium levels in the body through the action of the hormone it secretes, parathyroid hormone (PTH). When the parathyroid hormone levels are low then the blood calcium levels also decline. These parathyroid disorders may be inherited and therefore present from birth or acquired where it develops during the course of life.
Hypoparathyroidism may be a result of hereditary syndromes such as DiGeorge syndrome, Kearns-Sayre syndrome and Kenny-Caffey syndrome. Although several diseases (like autoimmune conditions) can cause hypoparathyroidism during the course of life, it is more often associated with medical or surgical causes (iatrogenic). Radiation to the neck, radioactive iodine or surgical removal are some of the other reasons for hypoparathyroidism.
Sometimes hypoparathyroidism occurs when the parathyroid glands are absent or shrinks (atrophy). This is known as idiopathic hypoparathyroidism. Another condition that needs to be considered is parathyroid hormone resistance where the body does not respond to PTH despite it being present. This is known as pseudohypoparathyroidism.
Chronic kidney disease can lead to hypocalcemia through several different mechanisms, depending on the type of kidney disease. Hypocalcemia may arise in kidney disease when there is loss of calcium in urine, reduced conversion of vitamin D to its active form and a reduction in calcitriol production with decrease in the absorption of calcium from the intestines.
Vitamin D Deficiency
Vitamin D plays a vital role in regulating calcium levels in the body by impacting on the action of parathyroid hormone (PTH). Therefore a vitamin D deficiency may lead to hypocalcemia. This deficiency is not uncommon and often associated with inadequate sunlight exposure, reduced intake of vitamin D (nutrition) as well as with chronic kidney disease that can affect vitamin D conversion.
Some of the other causes of hypocalcemia includes:
- Acute pancreatitis
- Hungry bone syndrome
- Liver disease
- Drugs such as certain anticonvulsants and cancer medication.
Treatment of Hypocalcemia
The treatment for hypocalcemia depends on the underlying cause as it is a consequence of some other disease which needs to be treated and managed.
- Calcium supplementation (oral) is usually necessary in severe and chronic hypocalcemia.
- Vitamin D supplementation may be required in hypocalcemia associated with vitamin D deficiency.
- Parathyroid hormone (PTH) when hypocalcemia is associated with hypoparathyroidism.
- Intravenous (IV) calcium gluconate may be necessary when there are serious symptoms such as tetany in severe hypocalcemia.
It is important to consult with a medical professional about proper calcium and/or vitamin D supplementation. Elevated levels of calcium in the blood (hypercalcemia) can also have a host of adverse effects in the body and cause a variety of symptoms. If the underlying cause of hypocalcemia is not properly diagnosed and managed then supplementation may only provide short term relief for hypocalcemia and sometimes in these cases supplementation alone may be inadequate.