In humans, calcium is the most abundant mineral and forms about 2% of our total body weight. Almost all of this calcium is found in the skeleton and the rest is found in the teeth, the blood plasma, the body’s soft tissues and the extracellular fluid.
The main role of calcium in the body is to provide structure and strength to the skeleton. This structure is mainly provided by a form of calcium phosphate called hydroxyapatite crystals, which are found in collagen. Calcium ions on bone surfaces interact with those present in the bodily fluids, therefore enabling ion exchange. This is essential in maintaining the balance of calcium in the blood and bone. Calcium in the blood is an important regulator of key bodily processes such as muscle contraction, nerve impulse signalling, hormone signalling and blood coagulation.
Sources of calcium
Calcium needs to be obtained from the diet as it is not manufactured by the body. The main sources of calcium in the diet are milk, dairy products and other calcium-rich foods such as fish with edible bones (e.g sardines and anchovies), beans, tofu, spinach, watercress and broccoli.
Some foods are also fortified with calcium such as milk, yogurt, breakfast cereals, rice, and even biscuits. Calcium can also be taken as a supplement and may be prescribed to lactating women or growing children, for example, to prevent deficiencies.
Calcium deficiency leads to poor bone health and may be caused by inadequate calcium intake, poor calcium absorption or excess calcium loss, all of which may reduce bone mineralization. Bone conditions such as osteoporosis and rickets are caused by a vitamin D deficiency, which impairs the intestinal absorption of calcium and, in turn, leads to a low rate of bone mineralization. The bones therefore become soft, pliable and prone to deformity.
Reviewed by Sally Robertson, BSc