Vitamin D can be considered either a vitamin or a hormone.
Vitamin D is essential for the absorption of calcium and phosphorus from the digestive tract and deposition in the bones.
By promoting calcium absorption, vitamin D helps to form and maintain strong bones.
25(OH)D is the active form of vitamin D which its primary role is to maintain blood calcium and phosphorus levels within a normal range.
It acts in the concert with two others hormones: parathyroid hormone (PTH) from the parathyroid glands and calcitonin from the thyroid glands.
It is also important for regulating cell differentiation and growth. It may also protective against colorectal cancer.
Vitamin D is formed from a substance present in our skin, called 7-dehydrocholestrol. This substance will be converted to cholecalciferol which then enters the bloodstream and travels to the liver.
It is a fat-soluble steroid hormone precursor that contributes to the maintenance of normal levels of calcium and phosphorus in the bloodstream.
The infant needs to be exposed to sunlight to permit the synthesis of vitamin D from the precursor in the skin.
Sensible sun exposure can provide an adequate amount of vitamin D which is stored in body fat during the winter, when vitamin D cannot be produced.
Since milk, human as well as cow’s, is not a good source of vitamin D, a small supplement is required for both breast-fed and bottle-fed infants.
Fish liver oil preparations are normally used as supplements for the supply of vitamins A and D.
Food sources of vitamin D come in natural and fortified forms. Fortified forms are included in milk, cereals, and some margarines.
Natural sources include fish oils, salmon, sardines, herring, egg yolks and liver.
Vitamin D : Functions and Food Sources