Recommended Nutrient Intakes for Vitamin and Minerals

Calcium

Functions

Calcium is the most abundant mineral in the body. 99% of calcium is found in the bone where it is an integral part of bone structure. It provides a rigid frame to hold the body upright and serves as attachments for muscle. Bone also provides a calcium bank which can contribute to blood calcium.

Calcium in the bone form hydroxyapatite crystals which give strength and rigidity to bone. These crystals are also present in teeth.

Although only 1% of the body's calcium circulates in fluid, it is vital to life. The calcium ion participates in the regulation of muscle contraction, the clotting of blood, the transmission of nerve impulses, the secretion of hormones, and the activation of some enzyme reactions. Calcium also serves as a cofactor in a protein that helps convey signals. Several of the messages it delivers help maintain normal blood pressure. Calcium may be useful for preventing and treating hypertension.

Recommended Intakes

Table: Recommended Intakes for Calcium (mg/day)

Food Sources

Calcium is found most abundantly in milk and milk products. Other sources of calcium include oysters, canned fish prepared with bones, almonds, tofu, vegetables (e.g. mustard and turnip greens, bok choy, kale, parsley, watercress, broccoli, some leafy green vegetables).

There are many factors that promote and inhibit the absorption of calcium.

Deficiency

A low calcium intake can impair the attainment of peak bone mass. This can lead to increased risk of fractures.

Toxicity

Ingestion of large amounts of calcium from calcium salts (e.g. calcium carbonate in antacids) can override the ability of the kidney to excrete unwanted calcium. This can cause hypercalcaemia and metastatic calcification of the cornea, kidneys and blood vessels. Individuals taking vitamin D may also suffer similar symptoms.