Vitamin D – Chemistry, Functions, Food Sources
Pure Vitamin D was isolated in crystalline form in 1930 and was called calciferol. It was also known as antirachitic vitamin.
Chemistry and Characteristics
Vitamin D is a group of sterol compounds possessing anti-rachitic properties, but only two are of nutritional interest.
- Vitamin D2 or Ergocalciferol found in plants and
- Vitamin D3 or cholecalciferol which occurs in animal cells and activates in the skin on exposure to ultraviolet light.
Pure vitamin D is white, crystalline compound which is soluble in fats and fat solvents, but insoluble in water. They are stable to heat, alkalies, and oxidation.
Functions
1. Vitamin D regulates the absorption of calcium and phosphorus from the intestinal tract and also calcification of bones and teeth. It believed that vitamin D renders the intestinal mucosa more permeable to calcium and phosphorus. Thus vitamin D is required for normal bone and teeth development.
2. Vitamin D regulates the enzyme ‘alkaline phosphatase’ which regulates the release of phosphate organic compounds.
Food Sources
Vitamin D occurs only in foods of animal origin. Fish liver oils are the richest natural source. Liver, eggs and butter contain useful amount. Small amounts are present in fresh milk and milk products.
Another cheap source of vitamin D is sunlight. Exposure to ultraviolet rays of the sunlight converts the precursor of Vitamin D (7dehydro-cholesterol) present in the skin, to its active form.
Recommended Dietary Allowances
The recommended daily allowance of vitamin D is not given by ICMR. If the exposure to sunlight is sufficient, deficiency symptoms are not seen. In case of inadequate exposure to sunlight, a daily supplement of 400 IU is recommended for adults.