Define Factors that Affecting the Calcium Absorption?

It is a well known fact that the amount of calcium that we eat need not be the amount of calcium that gets absorbed. The difference between the two is primarily due to certain factors which may hinder/enhance the absorption or bioavailability of calcium. Thus, the bioavailability of calcium can be defined as the fraction of dietary calcium that is potentially absorbable by the intestine and can be used for physiological functions, particularly bone mineralization or to limit bone loss. Several factors affect the proportion of dietary calcium absorbed by humans, also known as fractional absorption of dietary calcium.

The fractional absorption varies inversely with the quantity of calcium ingested. Lower the intake, higher the percentage of calcium absorbed. A study on healthy adult women, in which intakes were lowered from 2000 mg calcium per day to 300 mg per day (i.e. from 50 to 7.5 millimoles/day), the fractional whole body retention of ingested calcium, an index of absorption increased from 27% to 37%. It should be noted that this adaptation does not fully make up for the increased losses on higher intake. In absolute amounts, the women would have absorbed much more calcium on 2000 mg intake versus 300 mg. This adaptation was reported to take 2-3 weeks, and was accompanied by increase in 1, 25 di OH D₃, which as already seen, increases intestinal absorption of calcium.