Calcium Balance in a Healthy Body
Calcium is the most abundant mineral in the body. In a healthy person, each Kg of body weight includes about 22 gms of calcium. 99% of this calcium is in the bones.
Normal diet contains about 1000 mg of calcium in a day. About 400 mg is absorbed from the intestines. Intestines secrete about 150 mg and thus 750 mg is passed in stools.
About 9000 mg of calcium is filtered from the kidney. 8750 mg is reabsorbed and 250 mg is passed in the urine.
Approximately 800 mg of bone calcium moves into the extracellular space (intestinal secretions, blood, fluid in the space outside blood vessels, lymph etc) and similar amount moves back into bones.
Requirements in health change with age.
Requirements in children are
- Birth to 1 yr about 200- 250 mg,
- 1 to 3 yrs about 700mg,
- 4 to 8 yrs 1000 mg and
- during puberty 1300mg.
In adults upto 50 yrs of age about 1000 mg is sufficient. Man older than 70 yrs and pregnant woman under 18 yrs may require 200 mg extra.
Functions of calcium in the body
Calcium is required for bone formation.
It is also required essentially
for nerve and muscle function
( this includes cardiac rhythm and muscle activity),
various enzymatic processes in the cells,
and blood clotting.
Calcium is maintained in a very narrow range in the blood. The level in the cells is very low. Movement of calcium from outside to inside is required for electric current generation and contraction of muscles.
Low calcium level in the blood is called hypocalcemia.
A low calcium level in the blood gives rise to twitching of muscles, fits, spasm of hand and feet muscles etc. Reduced minerals in the bones cause rickets in children and weak bones in adults (osteomalacia) which can be painful and get fractured easily. This can happen with Vitamin D deficiency or if calcium is deficient in diet.
High levels of calcium are designated as hypercalcemia. High levels reduce kidneys ability to concentrate urine and more urine is passed. This can cause renal failure, deposition of calcium in kidney tissue (nephrocalcinosis) and stone formation. Recurrent stones may be a result of this.
Sources of calcium in the diet are milk, yoghurt (dahi, lassi, chhachh), Cheese, Tofu, almonds, cabbage, broccoli, turnip, green leafy vegetables and some varieties of fish (salmon, sardines)
Calcium supplements are available as calcium carbonate and calcium citrate. Usually, not more than 500 mg is taken daily. It can cause constipation and hence plenty of fluids should be taken with it. Very high doses of calcium can cause confusion, irritability, fits, stones, renal failure etc. These can interfere with antibiotics like ceftriaxone and antihypertensive drugs (calcium channel blockers).
There are large no of genetic and acquired diseases which result in abnormal calcium metabolism. These may need a consultation with a doctor for diagnosis and treatment.