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The Sun and Vitamin D

May 30, 2012

The debate around sunscreens and vitamin D is still running hot.  Are sunscreens causing vitamin D deficiencies?   How much sun is enough? When it comes to Vitamin D, is all skin created equal?   There are so many questions…

Thinking about our bodies again we notice that vitamin D is something that the body is equip to manufacture.  At the basal layer of our epidermis lies the answer for here sits 7-dehydrocholesterol ready to jump into action upon receiving a dose of UV.  Scientists have discovered that UVB is the best activator and more specifically that with a wavelength of 295-300nm.   However, it is very likely (though unproven) that while sitting in front of a UV lamp set at this specific wavelength may create the Vitamin D your body requires you would still fail to thrive – our bodies evolved under the sun in all it’s glory – chopping it up is akin to transporting yourself to mars.

Upon UV radiation the 7-dehydrocholesterol is transformed into Cholecalciferol.  This chemical has a half life of approximately 24 hours which means that while you may end up with heaps of this chemical floating around in your blood stream after a day at the beach, unless it is further reacted its benefits will be lost.

Cholecalciferol travels in the blood serum to the liver where it is further reacted to a chemical called 25-hydroxycholecalciferol which can be stored for several weeks.  Upon its release from here the pro-vitamins main job is to facilitate the intestinal absorption of calcium.

With regards to UV absorption it is important to note that the solar spectrum varies from hour to hour, day to day, month to month and year to year. Your geographical position in terms of latitude also counts and the general rule of thumb is if your shadow is longer than you are tall, you are not making much Vitamin D.

Interestingly there are some websites that state that you have to expose large parts of your body in order for it to produce enough vitamin D and that some skin is more efficient at producing than others.  While this may be true I have not found any solid evidence to either support or deny this.  It would seem logical to me that the skin on the face and hands would be adequately able to produce vitamin D, especially given the shear number of people who evolved in cold-climate areas and who would have had to either cover most of their skin or remain inside for large parts of the year.

So, should we eat vitamin D or make our own?

There are surprisingly few foods that are naturally rich in Vitamin D. The most abundant source can be found in Pink salmon and then other oily fish although you would have to eat substantial amounts on a daily basis to get enough.  Egg yolks contain a small amount, as do leafy green vegetables but other than that we have to rely on fortification and the implications of that.

Breakfast cereal, milk, orange juice and bread are just some of the foods regularly fortified with vitamin D in the form of D3 (Calcitrol). Once in the body this finds it way to the liver through blood plasma after it has been released from the food via the bowel epithelial cells which oxidise cholesterol.  Then it travels to the liver in the same way as your skin-made vitamin D so both sources are equally valid, just that one is more efficient (and cheaper just so long as the sun is available).

One potential down side of oral consumption, especially over-consumption is the tendency for excess vitamin D to be stored in fat cells.  It is not yet known if this could build up and pose a risk in terms of toxicity but it does make sense that again, moderation in both supplementation and consumption is exercised especially in light of the fact that Vitamin D acts as a cellular messenger for over fifty known cellular reactions.

Further it was interesting to read that alcohol impairs the body’s ability to synthetize vitamin D.

Diet and Vitamin D – there have been studies looking at the effect that diet has on MED. Fish oil (rich in vitamin D) does seem to boost the MED slightly as do the flavonoids in cocoa. A study on 199 black and 229 non-Hispanic white adults found vegetarian, partial vegetarian and non-vegetarians showed no difference in Vitamin D levels relating to the dietary habits of each group.

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