Explain the Bioavailability of nutrients?

The amount of many nutrients needed in the diet depends on the absorption or bioavailability of the nutrients. Bioavailability is defined as 'the percent of the dietary nutrient absorbed and utilized for a specific function by the body'. The percent absorption varies widely for different nutrients depending on the quantities ingested and the presence of other constituents of the diet. Examples are: iodine absorption is nearly loo%, calcium absorption in a normal adult is about 40% to 60% while that of iron varies from 1% to 15% , depending on the type of iron and other constituents of the diet. The concept of bioavailability is best illustrated by iron, Iron is present as inorganic iron in vegetarian foods and as organic iron in meat and flesh foods, The inorganic form of the iron, as you may already be aware, is known as 'non-haem iron' while the organic form is known as haem iron. The 'non-haem iron'' absorption is affected by several constituents of the diet while haem iron absorption is relatively independent of these constituents.