I usually do not like to write about a single vitamin or supplement. It seems too boring for me to have to research and for you to have to read. Usually, something like a general vitamin description would be easily accessible on the Internet and I see no reason for me to regurgitate what you could easily find elsewhere.
However, there is some very interesting research regarding vitamin D that can benefit our society on an assortment of levels. Unfortunately, the research into vitamin D’s potential is in its infancy: spurring many questions and theories with few answers thus far, and spurring controversy in the realms of the RDA’s recommendations. What’s all of the fuss about? Lets see…
The Sun Vitamin
It is summer time again, and that means barbecues, beaches, gardening and/or just spending more time outside. Many people are aware that with our increasing sun exposure comes an increase in the production of vitamin D in our skin. This is very beneficial for us as this is the optimal way our bodies can utilize vitamin D.
However, the media reminds us during this time of year that with an increase in sun exposure comes an increase in diagnoses of skin cancer because many do not protect ourselves enough from UV exposure of the sun. Recent research is now starting to suggest that although skin melanomas are certainly a danger with increasing unprotected-ultraviolet B exposure, the lack of vitamin D we would normally produce is just as dangerous. For example, since the 1980s, scientists have recognized that the risk of developing and dying of breast, colon, prostate, ovarian, and many other cancers is increased in relation to living at higher latitudes and being more prone to developing vitamin D deficiency.
Biologic Function
Before we dive in any deeper to what vitamin can do, lets understand what it is. The primary function of vitamin D in humans is to maintain intracellular and extracellular calcium and phosphorus. Vitamin D refers to two biologically inactive precursors – D3, also known as cholecalciferol, and D2, also known as ergocalciferol. The former, produced in the skin on exposure to UVB radiation (290 to 320 nm), is said to be more bioactive. The latter is derived from plants and only enters the body via the diet, from consumption of foods such as oily fish, egg yolk and liver.
Vitamin D made in the skin or ingested in the diet, however, is biologically inactive and requires obligate hydroxylations first in the liver to 25-hydroxyvitamin D (25(OH)D), and then in the kidney to 1,25-dihydroxyvitamin D (1,25(OH)2D). 25-Hydroxyvitamin D is the major circulating form of vitamin D that is the best indicator of vitamin D status. 1,25-dihydroxyvitamin D is the biologically active form of vitamin D.
Regulation of Vitamin D
Ever heard of somebody dieing from vitamin D toxicity because of too much sun exposure? No. That is because the production of vitamin D and its metabolism are tightly regulated by the body. Once vitamin D enters the circulation, it can be stored in fat cells for later use or metabolized in the liver to 25(OH)D. This hydroxylation step is feedback regulated, meaning that if there is too much 25(OH)D present, our body will store the vitamin D. If there is not enough, more 25(OH)D will be produced.
This fat-soluble hormone interacts with its specific nuclear receptor in the intestine and bone to regulate calcium metabolism. It is now recognized that the vitamin D receptor is also present in most tissues and cells in the body. 1,25-dihydroxyvitamin D, by interacting with its receptor in non-calcemic tissues, is able to elicit a wide variety of biologic responses. 1,25-dihydroxyvitamin D regulates cellular growth and influences the modulation of the immune system.
There is compelling epidemiologic observations that suggest that living at higher latitudes is associated with increased risk of many common deadly cancers. Both prospective and retrospective studies help support the concept that it is vitamin D deficiency that is the driving force for increased risk of common cancers in people living at higher latitudes.
Most tissues and cells not only have a vitamin D receptor, but also have the ability to make 1,25-dihydroxyvitamin D. It has been suggested that increasing vitamin D intake or sun exposure increases circulating concentrations of 25-hydroxyvitamin D, which in turn, is metabolized to 1,25-dihydroxyvitamin D(3) in prostate, colon, breast, etc. The local cellular production of 1,25-dihydroxyvitamin D acts in an autocrine fashion to regulate cell growth and decrease the risk of the cells becoming malignant. Therefore, measurement of 25-hydroxyvitamin D is important not only to monitor vitamin D status for bone health, but also for cancer prevention.