In the past, we have commonly seen people taking a “morning walk”. We have accepted this as a customary fitness lesson passed on from generation to generation. This should actually be considered to have been a blessing for us by our ancestors. However, nowadays, especially in the urban lifestyle, this morning walk has disappeared. Apart from the physical exercise, this “morning walk” would also provide us with extremely important exposure to the sun. Unknowingly, we were building up our stores of a very vital substance in our body, which was Vitamin D. This Vitamin D was initially considered to be affecting the bones and the musculoskeletal system only. It was known to be an active regulator of calcium metabolism in the body. However recent research indicates a much larger role being played by this Vitamin D. Vitamin D receptors have been found to be present on many other organs such as heart, kidney and lungs to name a few. Hence the role of Vitamin D in non-skeletal systems has now come to the forefront of researchers. Vitamin D is a fat soluble vitamin. It is also known as the “Sunshine Vitamin” because of the fact that most of the vitamin D in the body is produced in the skin on exposure to the ultraviolet radiations of the sun. On a biochemical level, Vitamin D is a secosteroid. It is produced from 7-dehydrocholesterol, found in the skin. The production and metabolic activation of Vitamin D is discussed ahead. 

In the human body Vitamin D is found mainly in 2 forms viz. 1. Vitamin D2 – Ergocalciferol and 2. Vitamin D3–Cholecalciferol. Both these are actually pro-hormones which are converted into the biologically active form of Vitamin D [Calcitriol], by a series of reactions. However even amongst these two forms, Cholecaliferol [Vitamin D3] is known to be the more potent and supplies almost 90% of the body’s requirement of Vitamin D. Cholecalciferol is generated by the human body in the skin on exposure to sunlight [ultraviolet radiation] whereas Ergocalciferol is available in foodstuffs and is absorbed from the intestine. Foods rich in Ergocalciferol are Mushrooms and Alfalfa, Salmon, tuna, and mackerel and fish liver oils are among the better sources of Vitamin D. Cod liver oil is considered the single best dietary source of Vitamin D. However, these sources are not sufficient to maintain the normal Vitamin D levels in the body in absence of proper exposure to sunlight. 

Normal range of vitamin D in the body

Vitamin D levels in ng/mL*

Health status

<10 – Vitamin D Deficiency

10–20 -Vitamin D insufficiency

30- 100- Adequate levels of Vitamin D

>100 -Vitamin D Toxicity

Production and Metabolic activation of Vitamin-D

Is portrayed in the following flowchart.

Vitamin-D