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Calcium as Mineral – Rich Food Sources, Functions, Deficiency & Daily Requirements

CALCIUM ( Ca ):

About half of calcium present in blood is in ionized from and the rest, in unionized from. Some of unionized calcium is bound to protein, and a small amount is bound to citrate.

Calcium taken in the diet is in the form of calcium phosphate or carbonate.

Sources:

  • Milk , eggs, fish, and vegetables,
  • Cereals (wheat and rice) contain only small amounts of calcium.

Daily requirement:

  • Adult : 0.5 gms
  • Pregnancy : 1.5 gms
  • Children: 1.0 gm .Serum level 2.1-2.6mmol/L.

Absorption:

  • Takes placed in the first and second part of duodenum against electric and concentration gradients.
  • Two mechanisms have been proposed for absorption of calcium. They are simple diffusion and active transport process involving energy and the Ca2+pump.
  • The factor which increases the calcium absorption are vitamin D, parathyroid hormone, acidity and amino acids such as lysine and arginine.
  • The factors which decrease the calcium absorption are phytic acids or hexaphosphates of inositol present in cereals, oxalates from leafy vegetables, malabsorption syndrome, and high phosphate content in foodstuff.

Functions:

  • Intracellular concentration of calmodulin modulates the intracellular calcium levels to maintain the various calcium-dependent reactions. Any excess calcium ions are removed out of the cell via protein.
  • Calcification of bones and teeth
  • In addition, it helps in the following biochemical and physiological activities.
  • Blood coagulation. Ionic calcium helps in the production of thromboplastin and in the conversion of prothrombin into thrombin. Thus, calcium plays a role in blood coagulation.
  • Action of enzymes. Several enzymes including lipase, succinic dehydrogenase, adenosine triphosphatase and certain proteolytic enzymes are activated by calcium.
  • Muscle contraction. Calcium ions neutralize the negative charge of myosin which then combines with action, to help contraction. Ca2+ ions also activate the myosin ATPase which in turn hydrolyzes the ATP to supply energy required for contraction.
  • Neuromuscular excitability. Calcium is essential for excitation of nerves.
  • Hormone action. Ca2+ serves as an intracellular secondary messenger of different hormones.
  • Membrane permeability. Membrane permeability generally is increased by calcium. This effect balances the opposite action of sodium and potassium capillary permeability.

Clinical manifestations:

  • Deficiency of calcium leads to rickets, osteoporosis, and hyperexcitability.

Hypercalcaemia:

  • It may occur in the following conditions:
  • Hyperparathyroidism
  • Multiple myeloma
  • Metastatic carcinoma of bone
  • Milk-alkali syndrome
  • Treatment with drugs such as diuretics
  • Hypervitaminosis D

Hypocalcaemia:

It is observed in:

  • Tetany
  • Hypoparathyroidism
  • Fanconi’s syndrome (disorder of tubular reabsorption)
  • Acute pancreatitis
  • Vitamin D deficiency
  • Chronic renal failure.

Applied aspects: 

  • If the level of ionic calcium falls, the nervous system becomes hyperirritable.
This could lead to tetany. On the other hand, high calcium content depresses nervous irritability. Thus, the administration of calcium salts is indicated in the alleviation of tetany.

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