Define about the Excretion of Calcium?
Calcium is excreted approximately in equal amounts in urine and through intestinal secretions. Bile and other secretions into the intestine account for 150 mg calcium per day of which 30% is reabsorbed. The minimum endogenous (from the body as distinguished from exogenous which is from the diet) excretion of calcium is thus 100 mg/day (2.5 inillimoles). Urinary calcium excretion varies greatly among individuals and varies from 2.5-6.0 millimoles/day (100-240 mg/day). Urinary and endogenous faecal calcium are not the only forms of excreted calcium; losses through skin, hair and nails also need to be taken into account (insensible losses).
Sweat losses are minimal, about 15 mg/day. Total calcium loss may thus amount to 350 mg/day. Moderate to high intakes of sodium increases renal excretion of calcium. An intake of 500 mg of sodium as sodium chloride was found to draw out 10 mg of calcium in the urine. One study in post menopausal women found a correlation between high urinary sodium excretion and increased bone loss from the hip. Another factor that increases urinary calcium losses is high intake of protein. In typically vulnerable groups like post menopausal women, in whom decreased oestrogen production is associated with accelerated bone loss, 3% of the skeletal mass per year, it is advisable to regulate sodium intake and avoid high protein intakes. However, the data are very insufficient to make any adjustments in requirements of the general population based on sodium intake. Reduced sodium intake can have other advantages such as control of high blood pressure.