Human body produces Vitamin D as a response to sun exposure. This is why this vitamin is often known as sunshine vitamin. Researchers have revealed that Vitamin D has several roles to play in human body. For example, it helps to support the health of the immune system, bones and teeth, and often plays its role in brain and nervous systems also. Vitamin D significantly regulates insulin levels and helps in diabetes management. Function of this vitamin in lung function and cardiovascular health is noteworthy. Besides these, it may also protect against a range of conditions such as cancer and multiple sclerosis.
Vitamin D is actually not a vitamin!
In our childhood days, we used to study that vitamins are special nutrients that cannot be generated by the body and as a result must be taken in through our diet. However, Vitamin D can be synthesized by our body itself when sunlight strikes our skin. Hence, it should be considered a pro-hormone and not actually a vitamin. Exposure of sun on bare skin for approximately 10 minutes, 4 times per week can generate sufficient of this vitamin. But report reveals that a considerable proportion of the global population is extremely Vitamin D deficient.
A brief history of Vitamin D
In the year 1914, two researchers from America Elmer McCollum and Marguerite Davis invented a compound in cod liver oil and they named it Vitamin A. In the year 1919, british doctor Sir Edward Mellanby, working with dogs noticed dogs that were fed cod liver oil did not develop rickets and concluded vitamin A, or a closely associated factor, could prevent the disease. In 1921 he wrote, “The action of fats in rickets is due to a vitamin or accessory food factor which they contain, probably identical with the fat-soluble vitamin.” In addition, he documented that cod liver oil was a brilliant antirachitic agent.
Elmer McCollum, in the year 1922, observed that modified cod liver oil, where Vitamin A had been totally destroyed, cured ill dogs. Hence he concluded that cod liver oil surely contained something special other than Vitamin A. McCollum named that special compound Vitamin D as it was the fourth vitamin to be named. No one realised at that point of time that this vitamin can be generated by human body through exposure to UV lights.
Goldblatt and Soames in the year 1923, claimed that when 7-dehydrocholesterol (later recognised as the precursor of Vitamin D) was irradiated with sunlight, a substance equivalent to the fat-soluble vitamin was generated. Alfred Fabian Hess and Weinstock stated in this way: Light equals vitamin D.
The chemical structures of the Vitamin D were determined in the 1930s in the laboratory of Professor Adolf Otto Reinhold Windaus at the University of Göttingen in Germany. Professor Adolf Windaus, in the year 1928, received Nobel Prize in Chemistry for his work on the constitution of sterols and their relationship with vitamins. In 1932, Vitamin D2 which could be produced by ultraviolet irradiation of ergosterol was chemically characterised and it was 1936 when Vitamin D3 was chemically characterised from the ultraviolet irradiation of 7-dehydrocholesterol.
Mark Haussler and Tony Norman in 1969, having studied nuclear fragments of intestinal cells, identified a specific binding protein for the vitamin known as Vitamin D receptor. Metabolism of Vitamin D to active forms, in which it was found to be converted to calcifediol in the liver, was discovered in the year 1972.
Calcifediol, also acknowledged as calcidiol, 25-hydroxycholecalciferol, or 25-hydroxyvitamin D (abbreviated 25(OH)D), is primarily a prehormone that is produced in the liver by hydroxylation of vitamin D3 (cholecalciferol) by the enzyme cholecalciferol 25-hydroxylase. That enzyme was isolated by American adult endocrinologist Michael F. Holick. Nowadays, medical practitioners measure this particular metabolite to monitor vitamin D status.
Important fact in this regard is that, full conversion of vitamin D3 to calcifediol takes approximately 7 days. Calcifediol is then converted by the kidneys to calcitriol, the biologically active form of vitamin D which circulates as a hormone in the blood, maintaining the concentration of calcium and phosphate in the bloodstream and promoting the healthy growth of bone.
