Some more on the TWO types of vitamin D. Also, I mispoke - it takes plae skinned individuals just a few mintues to make adequate vitamin D, but may take dark skinned persons hours to get the same equivalent. And also, my last post was written by Dr. Mercola - regardless of what you think of him, he is very well educated and seeks out experts in the field(s) in which he is writting to form his own opinion.
"By John Jacob Cannell, M.D., executive director of The Vitamin D Council
Vitamin D is a vital nutrient that is unique, both in terms of its physiology and because humans rely on both endogenous skin production and exogenous sources to meet biological requirements. Vitamin D is commercially available as vitamin D2, (ergocalciferol) [this is the synthetic form that is added to foods - it is not as biactive as D3 and toxic to some people] made from plant products, and vitamin D3, (cholecalciferol) made from animal products.
Cholecalciferol is also made naturally in the skin by the action of a specific wavelength of ultraviolet light (UVB) interacting with precholesterol. Cholecalciferol is then transported to the liver and turned into calcidiol [(25(OH)D]. In turn, the calcidiol is transported to the kidney and transformed into the steroid calcitriol, which is excreted into the blood to help regulate calcium in the body. This is the main endocrine function of vitamin D.
Meanwhile, many tissues other than the kidney turn calcidiol into calcitriol to help regulate gene expression locally; this is the newly discovered autocrine (inside the cell) and paracrine (surrounding the cell) functions of vitamin D. This autocrine and paracrine function is impaired in vitamin D deficient subjects. All studies show many Americans are vitamin D deficient, especially Blacks, where the problem is pandemic.
This use of calcitriol by other tissues as an autocrine and paracrine hormone is a relatively new discovery that explains its role in human development as well as the many health benefits of vitamin D in other illnesses such as diabetes, hypertension, heart disease, autoimmune illness, at least 13 different cancers and, perhaps, some mental illness.
The Extraordinary Rate of Natural Vitamin D Production
The single most important scientific fact about vitamin D is that young adult Whites make about 20,000 units of vitamin D in their skin within minutes of whole-body, summer-sun exposure. This is 100 times the Adequate Intake (AI) and five times the toxicity maximums (Lowest Observed Adverse Effects Level or LOAEL) recommended by the Institute of Medicine (IOM) for young adults. Therefore, many Americans greatly exceed the IOM?s safety recommendations by simply spending a few minutes outside in their swimming suits!
This extraordinary rate of natural vitamin D production in the skin (20,000 IU) leading to the production of a potent endocrine, paracrine and autocrine steroid hormone leads one (as T.S. Eliot once said), “to an overwhelming question.” Why did Nature design such a complex system reliant on rapid and bountiful production of cholecalciferol? Answer, “Probably for a very good reason.”
Because low calcidiol [25(OH)D] levels (less than 35 ng/ml) are associated with so many chronic illnesses, calcidiol levels are an important part of any laboratory health evaluation and should be routinely checked by physicians. Unfortunately, few physicians are aware of this so perhaps as much as 70 percent of the U.S. population has calcidiol levels below 35 ng/ml. Even when asked to check vitamin D levels, physicians often order calcitriol levels, instead of calcidiol levels, an error that greatly misleads both the physician and the patient."
TS
