What happens when calcium levels in our body are low?

What happens when calcium levels in our body are low?

Inadequate intake of dietary calcium from food and supplements produce no obvious symptoms in the short term. Circulating blood levels of calcium are tightly regulated. Over the long term, inadequate calcium intake causes osteopenia which if untreated can lead to osteoporosis. The risk of bone fractures also increases, especially in older individuals. Calcium deficiency can also cause rickets, though it is more commonly associated with vitamin D deficiency.

Causes of hypocalcemia:
• Vitamin D inadequacy or vitamin D resistance
• Hypoparathyroidism following surgery
• Hypoparathyroidism owing to autoimmune disease or genetic causes
• Renal disease or end-stage liver disease causing vitamin D inadequacy
• Pseudohypoparathyroidism or pseudopseudohypoparathyroidism
• Metastatic or heavy metal (copper, iron) infiltration of the parathyroid gland
• Hypomagnesemia or hypermagnesemia
• Sclerotic metastases
• Hungry bone syndrome postparathyroidectomy
• Infusion of phosphate or citrated blood transfusions
• Critical illness
• Drugs (eg, high-dose intravenous bisphosphonates)
• Fanconi syndrome
• Past radiation of parathyroid glands
Adapted from: Fong, Khan. Updates in diagnosis and management for primary care. Canadian Family Physician.2012;58:158-62

Hypocalcemia is a common biochemical abnormality that can range in severity from being asymptomatic in mild cases to presenting as an acute life-threatening crisis. Serum calcium levels are regulated within a narrow range (2.1 to 2.6 mmol/L) by 3 main calcium-regulating hormones—parathyroid hormone (PTH), vitamin D, and calcitonin—through their specific effects on the bowel, kidneys, and skeleton. Approximately half of the total serum calcium is bound to protein, and the remaining free ionized calcium is physiologically active. Hypocalcemia has also been associated with many drugs, including bisphosphonates, cisplatin, antiepileptics, aminoglycosides, diuretics, and proton pump inhibitors; as well, there are other causes.¹

Once the deficiency has set in, how do we correct Calcium to recommended levels?

They are many sources of calcium available for treatment of calcium deficiency. Milk, minerals comprised mainly of calcium phosphate; organic salts like tricalcium citrate, calcium lactate, calcium lactate gluconate and calcium gluconate and inorganic salts like calcium chloride, calcium carbonate and calcium phosphate Oral calcium and vitamin D and its metabolites are essential in management, in addition to correction of hypomagnesemia. Calcium carbonate and calcium citrate have the greatest proportion of elemental calcium (40% and 28%, respectively) and are easily absorbed; they are considered the supplements of choice. The maximum dose of elemental calcium that should be taken at a time is 500 mg.² In clinical practice, to obtain optimal clinical outcomes related to calcium supplementation, the dose of calcium should not exceed 500 mg at 1 time. It may be beneficial to supplement in smaller doses 4 times per day to lower PTH levels and decrease bone resorption. Absorption of calcium is greatest when taken in a dose of 500 mg or less.

Calcium supplements are generally well tolerated; however, some patients complain of gastrointestinal symptoms, including constipation, gas, flatulence, and bloating. Hypercalcaemia and hypercalciuria are uncommon. Calcium salts may decrease the absorption of iron, zinc and strontium ranelate. Consequently, iron, zinc or strontium ranelate preparations should be taken two hours before or after calcium carbonate. The absorption of quinolone and tetracycline antibiotics may be impaired if administered concomitantly with calcium. Quinolone antibiotics should be taken two hours before or after intake of calcium. If patient is on a bisphosphonate this preparation should be administered at least three hours before the intake of oral calcium since gastrointestinal absorption may be reduced. Thiazide diuretics reduce the urinary excretion of calcium. Due to increased risk of hypercalcaemia, serum calcium should be regularly monitored during concomitant use of thiazide diuretics.²

Calcium is the most obvious and persistent of the micronutrients, the fifth most abundant element in the body. Calcium is an important mineral component of our diet. Calcium supplementation can play a valuable role in bone health throughout the lifecycle. Calcium from carbonate and citrate should be the forms of select for supplementation. An adequate calcium intake through proper selection of calcium salt is therefore only one of many measures to ensure a healthy skeleton.

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References:

1. Fong, Khan. (2012). Updates in diagnosis and management for primary care. Canadian Family Physician,58:158-62
2. Trailokya A., Srivastava A., Bole M., Zalte N. (2016). Calcium and Calcium Salts. Journal of Association of Physicians of India.