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What causes low calcium level?

The short answer:

Low calcium blood level (Hypocalcemia) may result from parathyroid gland problems, vitamin D deficiency, low calcium intake in the diet, and drug-induced low calcium level. Find more about the main causes and symptoms of low calcium level in this article.

Key facts:

  • Calcium is an important electrolyte that plays important roles in normal cell function, neural transmission, membrane stability, bone structure, blood coagulation, and intracellular signaling.
  • The normal calcium blood level range from 8.5 to 10.5 mg/dl.
  • The low calcium blood level is known as hypocalcemia.
  • Hypocalcemia is defined as when your total serum calcium is lower than 8.5mg/dL ( 2.20 mmol/L).
  • The main causes of hypocalcemia are parathyroid gland problems, vitamin D deficiency, low calcium intake in your diet, and drug-induced low calcium level.
  • Symptoms of hypocalcemia are mostly related to the functions of your muscles and cardiovascular neurological systems and mental states.
  • Signs and symptoms of hypocalcemia include tetany, seizures, diminished to absent deep tendon reflexes, papilledema, mental problems (weakness, fatigue, irritability, memory loss, confusion, delusion, hallucination), and skin changes.

Function of calcium

What does low calcium mean?

Causes of low calcium level?

Symptoms of low calcium in your blood?

What are the main functions of calcium in your body?

Calcium is among the most abundant electrolytes in your body.

It makes up about 1.5 to 2% of your total body weight. Approximately 1,200 g of calcium is present in the body of an adult human and more than 99% of that amount is found in bones (Ref).

The main functions of calcium in your body are the following:

  • It plays an important role in normal cell function.
  • Calcium is important for bone and teeth structure.
  • It is important in neural transmission.
  • Calcium is important for muscle contraction.
  • It is involved in blood clotting.
  • Help in keeping a normal heartbeat.
  • It is required for the release of hormones and chemicals.

Calcium in your blood exists in three forms

  1. The ionized free active form (physiologically active).
  2. Non-ionized calcium, calcium bound to plasma proteins such as albumin.
  3. Non-ionized calcium, calcium complex with other ions such as bicarbonate, lactate, phosphate, and citrate.

What does a low calcium level mean?

  • Low blood calcium level is commonly known as hypocalcemia. It is a relatively common electrolyte disturbance that occurs in a broad spectrum of patients from asymptomatic to critically ill.
  • Hypocalcemia can affect people of all ages, including infants.
  • Calcium is maintained within a fairly narrow range from 8.5 to 10.5 mg/dl (4.3 to 5.3 mEq/L or 2.2 to 2.7 mmol/L) (Ref).
  • Hypocalcemia is defined as total serum calcium lower than 8.5mg/dL (< 2.20 mmol/L) or as ionized serum calcium lower than 4.7 mg/dL (1.17 mmol/L) (Ref).

What are the main causes of low calcium blood level (Hypocalcemia)?

Many health conditions could decrease your calcium blood level, however, it is commonly caused by abnormal levels of parathyroid hormones and vitamin D or problems with calcium and vitamin D absorption and elimination (Ref).

Causes of hypocalcemia

  1. Inadequate vitamin D production and action
  2. Hypoparathyroidism (parathyroid hormones deficiency)
  3. Hypomagnesemia
  4. Alcohol overconsumption
  5. Drug-induced hypocalcemia
  6. Pancreatitis
  7. Vitamin D deficiency

Vitamin D deficiency

Vitamin D deficiency may result from the following (Ref):

  • Nutritional deficiency of vitamin D
    • A diet deficient in vitamin D increases your risk to develop a low calcium blood level. So, the fortification of milk, cereals, bread, and other foods with vitamin D is critical, especially for children to avoid vitamin D deficiency.
    • Vitamin D deficiency or resistance may be induced by certain drugs such as phenytoin, phenobarbital, carbamazepine, isoniazid, theophylline, glutethimide, and rifampin.
  • Lack of sunlight absorption
    • Patients who are unable to be exposed to sunlight (solar ultraviolet B radiation) are at higher risk for developing vitamin D deficiency.
  • Malabsorption of vitamin D
    • Vitamin D is a fat-soluble vitamin and its absorption could be affected by many health conditions such as hepatic dysfunction, sprue, Crohn’s disease, and gastric bypass surgery as a result, the blood concentration of 25-hydroxy (25[OH]) Vitamin D is decreased.
  • Renal diseases
    • Nephrotic syndrome is commonly associated with the loss of a large amount of vitamin D in urine as a conjugate with large protein.
    • Also chronic renal failure with a reduction in glomerular filtration rate increase calcium loss in urine.

Parathyroid gland disorder

  • Parathyroid glands are four small pea-sized glands behind your thyroid in your neck.
  • Low levels of PTH cause low levels of calcium in your body.
  • Hypoprathryoid may be due to
    • No parathyroid glands at birth (congenital absence of parathyroid glands).
    • Post thyroidectomy (removal of the parathyroid gland during removal of thyroid glands by mistake).
    • Post-parathyroidectomy (surgical removal of thyroid glands).
    • Decrease secretion of parathyroid hormones which means a low level of parathyroid hormone.

Hypomagnesemia and hypermagnesemia

  • Both hypomagnesemia and hypermagnesemia may cause low calcium blood levels.
  • Hypomagnesemia means Low magnesium blood levels which could affect the secretion of parathyroid hormones as your parathyroid glands need magnesium to release parathyroid hormones.
  • Also, severe acute hypermagnesemia can cause hypocalcemia by both suppressing parathyroid hormone secretion and blunting its peripheral actions.

Alcohol overconsumption

  • Excessive alcohol consumption has been associated with hypocalcemia.
  • A study showed that true hypocalcemia was reported among 14.2 % of patients with alcohol abuse. Alcohol consumption decreases the secretion of parathyroid hormones leading to hypocalcemia.

Low calcium blood level results from other diseases

  • Small intestine diseases could decrease the absorption of calcium and vitamin D
  • Kidney diseases increase calcium loss
  • Liver diseases
  • COVID-19

Drugs-induced low calcium blood levels

  • Certain drugs could lower your calcium blood levels such as the follwoing (Ref):
    • Antibiotics as rifampin
    • Antiseizure drugs (such as phenytoin and phenobarbital)
    • Bisphosphonates (such as alendronate, ibandronate, risedronate, and zoledronic acid),
    • Calcitonin
    • Chloroquine
    • Corticosteroids
    • Propylthiouracil
    • Plicamycin
    • Foscarnet
    • Proton pump inhibitors and H2-receptor antagonists
    • Calcium channel blockers

A study reported that  IV administration of Bisphosphonates (pamidronate 45 mg) to breast cancer patients with bone metastases was associated with a 17% incidence of hypocalcemia, all of which cases were asymptomatic.

Also, drugs such as proton pump inhibitors (PPIs) and H2-blockers, by reducing gastric acid production may reduce calcium absorption leading to hypocalcemia as calcium absorption occurs in acidic conditions (Ref).

Moreover, glucocorticoids inhibit calcium absorption in the intestine and stimulate tubular calcium excretion increasing renal calcium loss and inducing hypocalcemia (Ref).

Low calcium blood levels due to pancreatitis

About  15% to 88% of people who have acute pancreatitis will develop hypocalcemia. However, the exact mechanism of hypocalcemia in acute pancreatitis is unknown.

The proposed mechanism for hypocalcemia due to pancreatitis is the autodigestion of mesenteric fat by pancreatic enzymes and the release of free fatty acids, which form calcium salts, and hence lower your calcium blood level (Ref).

What are the symptoms of low calcium blood level?

Symptoms of hypocalcemia can be classified according to the calcium blood levels

Symptoms of mild hypocalcemia

  • Muscle spasms and cramps especially in your back and legs
  • Brittle nails
  • Dry skins
  • In the case of untreated hypocalcemia, neurological and psychological symptoms results include:
    • Confusion
    • Hallucination
    • Memory defects
    • Irritability and restlessness
    • Depression

Symptoms of Severe hypocalcemia

  • Severe hypocalcemia may be associated with the following symptoms
    • Muscle aches
    • Tingling of your tongue, lips, and fingers
    • Tetany (spasm and stiffening of your muscles
    • Cardiac arrhythmia
    • Congestive heart failure
    • Seizure

Symptoms of low calcium blood levels can be classified according to body systems.

  • Cardiac symptoms
    • Congestive heart failure
    • Cardiomyopathy
    • Cardiac arrhythmia
  • Effect on mental status
    • Confusion
    • Disorientation
    • Psychosis
    • Fatigue
    • Anxiety
    • Poor memory
    • Reduced concentration
    • Personality disturbances
    • Irritability
    • Impaired intellectual ability
  • Neuromuscular irritability
    • Paresthesias
    • Tetany
    • Seizures (focal, petit mal, grand mal)
    • Muscle cramps
    • Muscle weakness
    • Laryngospasm
    • Bronchospasm
    • Parkinsonism
    • Dystonic spasms