Tuesday, 26 April 2011

Vitamin D

Back in February I had my regular blood test as usual. The lovely nurse, whom I usually see, told me that due to low light levels in Manchester, many people here often have vitamin D deficiency. I thought this was an interesting fact and strange I hadn't known about or heard about it before. Then, by sheer coincidence the results of my blood test revealed that I am indeed currently deficient in vitamin D. I thought this was an interesting fact and strange I hadn't known about or heard about it before. (Do I think my nurse is clairevoyant, lol,hell no!). I find this so hard to believe, now in April given the heatwave we are going through and the fact I have been out running in it everyday. I thought it would be nice to research and write a post on this vitamin just touching on its chemistry. I, myself, only knew what most people generally know I think, without looking anything up. That is, it is made in the skin when it is exposed to UV light. Deficiency among other things can produce brittle bones. Not good news for me since I recently ran the Brighton marathon. This is about as much as I knew about it anyway. It is a fat soluble vitamin, and in the skin, 7-dehydrocholesterol, a derivative of cholesterol is photolysed by UV light producing previtamin D3. The biologically active form being known as calcitrol. When synthesised in the kidney's it regulates among other things, the conc of calcium and phosphate in the bloodstream thus promoting the healthy mineralisation, growth and remodelling of bone. There are several types collectively, known as calciferol. I seem to be taking vitamin D3 or cholecalciferol. Chemically, the various forms of vitamin D are secosteroids i.e. steroids in which one of the bonds in the steriod rings is broken.The structural difference between vitamin D2 and vitamin D3 is in their side chains. The side chain of D2 contains a double bond between vitamin D2 and vitamin D3 is in their side. The side chain of D2 contains a double bond between carbons 22 and 23, a methyl group on carbon 24. It is a derivative of ergosterol, a membrane sterol and is produced by some organisms of phytoplankton, invertebrates and fungi in response to uv irradiation, D2 is not produced by land plants or vertebrates.
I found the following history interesting. The photosynthesis , of vitamin D evolved over 750 million years ago and played a critical role in the maintenance of a calcified skeleton in vertebrates as they left their calcium-rich ocean enviroment for land over 350 million years ago.

Vitamin D can only be synthesised via a photochemical process so early vertebrates that ventured onto land either had to go ingest foods that contained vitamin D because melanin in the skin hinders vitamin D synthesis.
One of the most important roles of vitamin D is to maintain skeletal calcium balance by promoting calcium absorption in the intestines, promoting bone resorption by increasing the osteoclast numbers, maintaining calcium and phosphate levels for bone formation, and allowing proper functioning of parathyroid hormone to maintain serum calcium levels. Historically, vitamin D3 was used to treat tb patients but has not been adequately investigated in controlled clinical trials.
Interestingly, vitamin D3 has also shown some anti-hiv -1 effects  in vitro , including the induction of  autophagy. In an epidemiological study of hiv positive women in tanzania, there appeared to be a correlation between reduced levels of vitamin D and speed of hiv disease progression. It is important to note that this still needs confirmation. To get deep into the chemistry, please look at this link


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