Vitamin D in a nutshell
Vitamin D is in fact a pro-hormone rather than a vitamin as such. This means that it only becomes active and serves its purpose after absorption and metabolism within the body. It comes in many forms, labeled from Vitamin D1 to Vitamin D5. Of these, vitamin D2 obtained from plant sources and also referred to as ergocalciferol and vitamin D3 obtained from animal sources and referred to as cholecalciferol are of interest to humans. The most important form is however Vitamin D3, cholecalciferol, rather than vegetarian form Vitamin D2, ergocalciferol.
Vitamin D is essential for proper functioning of the immune system, cell growth modulation, maintaining adequate serum levels of calcium and ensuring the absorption of calcium by bone tissue, in order to build strong bones. Vitamin D deficiency ultimately leads to brittle bones, osteoporosis, malformation of bones, malfunctioning of the immune system and neuromuscular dysfunction as well as increased inflammation levels throughout the body.
Sources of Vitamin D
Since it is a fat soluble molecule, it can be obtained mainly from fatty foods: mostly from fatty fish such as salmon, mackrel, sardines and to a lesser extend from full fat dairy products. It’s absorption by food ingestion is however very limited though. It is mainly synthesized by the skin under influence of sun exposure, and vitamin D receptors to this purpose are omnipresent in the body. In fact as much as 80-90% of its requirement is formed by synthesis in the skin via sun exposure.
And that is where the culprit is: at the same time sun exposure, UV radiation, is a known risk factor for skin cancers and metastatic melanomas. It is advised to use sunscreens with high SPF (sun protecting factor) to block UV radiation. Incidentally this seems to also be blocking vitamin D synthesis: a SPF of only 15 could block 99% of the vitamin D producing UV rays.
According to a review published in the Journal of the American Osteopathic Association the use of sunscreens contributes to the widespread vitamin D insufficiency major parts of the population are presently showing.
Therefore researches suggest that, depending on skin type, geographic area as little as 5 to 30 minutes of sun exposure twice a week to face, arms and legs without the use of sunscreen, would be adequate to provide sufficient vitamin D synthesis. Overexposure to sunlight, such as prolonged sunbaths, however is absolutely to be avoided because of the health concerns about skin cancer.
A good quality vitamin D supplement along with good nutrition behavior is equally recommended to those with very limited sun exposure or very fair skin needing maximum protection.
Once again: good lifestyle and nutrition patterns, with variety, moderation and physical activity as keywords, are the best sources of good quality health status.