This vitamin D metabolism image from Google images is probably one of the most shared and viewed.
So my own skin produces vitamin D from sunlight, why should I buy one.? This is the most common question encountered by most of my orthopedic colleagues.
Vitamin D metabolism as shown in the picture , isn’t that simple. It needs adequate 7dehydrocholesterol under the skin, an adequate quantity of sunlight, enough time for the sun to convert, UV-B type of radiation, as it is a fat-soluble vitamin will need fat to absorb from the gut, healthy liver and kidney to convert it into active vitamin D.
So if all these are in the right proportion, probably you can survive the vitamin D scare.
UV-B radiation is maximum between 10 AM and 4 PM, as the sunlight is more vertical than tangential at this time of the day delivering UV-B.
We Indians generally have darker skin tone compared to the western population, so high melanin content in our skin acts as a natural sunscreen. So 45 minutes of direct sunlight with bare arms, legs, face, and neck is essential to meet the required daily allowance of vitamin D.
So with the exception of those who perforce need to work outdoors in sunlight, most Indians do not get adequate sunlight to produce vitamin D endogenously. But our cultural taboo to cover most part of the skin with the dress and the undying desire of most of our population to become fair with the use of sunscreen has also led to the ill fate of our body’s factory to synthesize vitamin D.
Not to mention the urbanization of the population, living in an overcrowded tenement and high storied buildings without direct exposure of sunlight, pollution in the atmosphere, lack of outdoor activity, using umbrellas, avoiding sunlight on sunny summers due to the discomfort of scorching heat have all led to the deficiency epidemic.
Therefore in the Indian scenario, vitamin D sufficiency cannot be achieved entirely depending on sunlight.
(Contd – how did vitamin D evolve over the years..?)