Vitamin D is the sunshine
vitamin that has been produced on this earth for more than 500 million years. During exposure to sunlight
7-dehydrocholesterol in the skin absorbs UV B radiation and is converted to
previtamin D3 which in turn isomerizes into
vitamin D3.
Previtamin D3 and
vitamin D3 also absorb UV B radiation and are converted into a variety of photoproducts some of which have unique biologic properties. Sun induced
vitamin D synthesis is greatly influenced by season, time of day, latitude, altitude, air pollution, skin pigmentation,
sunscreen use, passing through glass and
plastic, and aging.
Vitamin D is metabolized sequentially in the liver and kidneys into
25-hydroxyvitamin D which is a major circulating form and
1,25-dihydroxyvitamin D which is the biologically active form respectively.
1,25-dihydroxyvitamin D plays an important role in regulating
calcium and
phosphate metabolism for maintenance of metabolic functions and for skeletal health. Most cells and organs in the body have a
vitamin D receptor and many cells and organs are able to produce
1,25-dihydroxyvitamin D. As a result
1,25-dihydroxyvitamin D influences a large number of biologic pathways which may help explain association studies relating
vitamin D deficiency and living at higher latitudes with increased risk for many
chronic diseases including
autoimmune diseases, some
cancers,
cardiovascular disease,
infectious disease,
schizophrenia and
type 2 diabetes. A three-part strategy of increasing food fortification programs with
vitamin D, sensible sun exposure recommendations and encouraging ingestion of a
vitamin D supplement when needed should be implemented to prevent global
vitamin D deficiency and its negative health consequences.