Calcium

Calcium is an essential macronutrient. It plays an integral role in building and maintaining bones and teeth, supporting their structure and function. Calcium irons are required for vascular contraction and vasodilation, muscle function, nerve transmission, intracellular signaling and hormonal secretion.

Absorption
When consumed in food, only about 30% of the calcium consumed is absorbed. Vitamin D, obtained both from exposure to sunlight and through the diet, improves calcium absorption. Some other components found in food such as phytic acid and oxalic acid can inhibit the absorption of calcium by binding to it. On the other end, a high sodium intake increases the excretion of calcium. High protein intake increases the excretion of calcium but also increases its absorption so there is no net effect. Caffeine and alcohol intake can reduce the absorption and increase the excretion of calcium, but only very high dosages of them would have noticable effects.

Hypocalcemia (Calcium Deficiency)
Calcium deficiency would not be immediately noticable because the supply used most important function, molecular signalling, is carefully regulated by the supply in bone. Symptoms of hypocalcemia include numbness and tingling in the fingers, muscle cramps, convulsions, lethargy, poor appetite, and abnormal heart rhythms. Untreated, hypocalcemia leads to death.

Hypercalcemia (Calcium Overdose)
Hypercalcemia is more often caused by disease than very high calcium intake, but when it is the latter it is usually because people are consuming calcium from food and taking supplements. Symptoms of hypercalcemia include constipation and increased risks for certain conditions, and potentially lower absorption of iron and zinc. The tolerable upper intake levels for calcium are 2-3 times the recommended daily intake, depending on age.

Calcium-Iron Interactions
See Calcium-Iron Interactions on the page for Iron.