For the better half of the last century we have been told that the sun is our enemy. It gives us skin cancer and that the smartest thing we could do was slather on thick layers of sunscreen, wear a hat, and avoid sunburn. Unfortunately, as often happens in our society, the pendulum now seems to have swung too far. Research definitely tells us that sunburn is a bad bad thing. Even just one severe sunburn in childhood can raise your risks of developing skin cancer as an adult by a significant amount. But in our "go big or go home" rush to avoid the sun we have inadvertently caused most of us to become vitamin D deficient.
You have probably heard that we get vitamin D from the sun. Actually, it's a little more complicated than that. Vitamin D starts as a molecule called 7-dehydrocholesterol (yes, it's based on that same cholesterol you hear all the hype about). When 7-dehydrocholesterol gets into the blood vessels just under your skin, and you happen to be out in the sun, the UV rays trigger a reaction to produce cholecalciferol (coal-aay-cal-sif-fur-awl). This reaction takes about 10 minutes to really get underway and a whole day's worth of vitamin D can be produced in about 15-20 minutes of moderate sun exposure (this rate varies based on skin type- faster for lighter skin, longer for darker), but after too long in the sun your body does a very smart thing. Vitamin D in high doses can be toxic so your body naturally starts limiting the reaction. This means that more than 20 minutes is no longer beneficial in raising your vitamin levels and can actually start destroying more than is being made. When you get tan you make this reaction take longer by absorbing more of the light in higher layers of your skin with the pigment melanin. So tanning (among other things) is your body's natural way of protecting you from too much vitamin D if you are someone who spends a lot of time in the sun. For most of us in the US it would be easy to get our daily allotment of Vitamin D from the sun during the summer, but in the winter things get a little more tricky. Not only are the days super short, but if you live above about the 30th parallel (which includes most of the US except Southern Florida and Hawaii) the sun doesn't even get high enough in the sky during the winter to penetrate the atmosphere with enough strength to trigger the reaction in the skin. So even if you live in a sunny area and get out there naked in the freezing cold you sadly won't be producing enough Vitamin D to qualify for a day's allotment.
So back to our story of how your body actually makes Vitamin D. After the sun hits your skin and makes cholecalciferol it then travels to your liver where another reaction happens which changes it ever so slightly into a molecule called (boringly) 25-hydroxycholecalciferol. This then goes to the kidney where it undergoes yet another change to become 1,25-dihydroxycholecalciferol. Woohoo! We made it to the active form of the vitamin! This form only lasts approximately 2-4 hours in circulation before it begins to break down and you have to start the process all over. As you can imagine, with this kind of complicated path there are a whole host of things that can go wrong! So besides not getting enough sun, people can be low on vitamin D if they are missing any of the pieces of this puzzle.
The primary function that has been conventionally assigned to vitamin D is in bone formation. You need proper amounts of Vitamin D in order to even absorb, let alone use calcium and all the other fabulous bone building minerals. Vitamin D actually turns on a gene which makes protein in your gut that binds to calcium to allow your body to absorb it. Vitamin D has also been shown to protect against cavities (for some of the same great reasons why it's so good for your bones). In fact, in one study looking at over 3000 children from 1920-1980 researchers found a 50% reduction in cavities in the kids with adequate Vitamin D.
For thousands of years people in colder latitudes have eaten traditional foods that supply Vitamin D during the cold winter months. Vitamin D is a fat soluble vitamin which means.... surprise... that you find it in fats! Cod liver oil, lard, whale fat, dairy, meat (not lean and often organ in nature) all these yummy (?) favorites are great traditional sources of Vitamin D. If you've read my fats blog then you'll know how fabulous fat soluble vitamins are, and Vitamin D is no exception! Among other things it acts as an anti-oxidant (yes, just like blueberries) and helps to protect your tissues from those nasty free radicals. It is also considered a "prohormone" which then gets converted into... you guessed it.. a hormone! Researchers have found vitamin D receptors on virtually all of the body's cells. You wouldn't expect to see that many receptors if it wasn't a pretty important thing! You don't have to look far to see what happens when your body lacks Vitamin D. The disease rickets, where your bones fail to form normally, is the manifestation of a severe Vitamin D deficiency, but Vitamin D deficiency has been associated with a host of other diseases like multiple sclerosis (MS), diabetes type I (the autoimmune version), and the biggie: cancer. Not surprisingly, 84% of patients who go to the Cancer Treatment Centers of America are deficient in Vitamin D.
Like I said above, we know that severe sunburn can increase your risk of skin cancer. In fact, sun exposure in general increases your risk of skin cancer simply because those same UV rays that convert the vitamin D also can hit things like your DNA and trigger mutations which then lead to cancer. However, medicine is now starting to find out how much protection the sun gives us from cancer via..... Vitamin D! Among the cancers that Vitamin D has been shown to protect against: breast, prostate, ovarian, colon... the list goes on.... and these are not minor cancers! These are the biggies that require intense treatment and often come back again and again. Skin cancer, on the other hand is easily treated by removal (duh, skin is a lot easier to reach than your ovary) and is much more sensitive to conventional cancer treatments (you can see it, therefore radiation can too). Plus you can easily observer skin cancer and therefore it is much more frequently found in routine screenings or by the person themselves and is caught at earlier stages (which means it's easier to treat). These differences in cancer types and treatability are significant and have everything to do with figuring out the cost-benefit ratio for sun exposure. One recent study concluded that the protection that Vitamin D gave against some of those nasty internal cancers listed above far outweighed the related increased risk of skin cancer from moderate sun exposure (not counting those nasty burns)! Let me say that again because I know it took me re-reading it a few times before it sunk in. With moderate sun exposure, your risks of all sorts of nasty internal cancers goes way down and your risk of skin cancer only rises slightly. Wow! Ahhhh... this is making me crave a little sunshine... too bad it's midnight in Portland!
So how does Vitamin D do all this cancer magic? Does anyone know? Yes! There have been multiple studies looking at the so called "mechanism of action" of this fabulous vitamin and it largely has to do with it's hormonal function (remember I told you it was a hormone). Not only does it turn on the genes that cancer turns off (mainly those that stop the cell from self-destructing when it realizes things have gone awry), it also turns on anti-cancer genes (specifically one called p53). Vitamin D also helps to keep your whole cell cycle functioning properly. This is the grow-->divide-->grow-->divide....die cycle of your cells. If this malfunctions and things start to grow, and grow, and GROW you get tumors, so keeping the cycle turning properly is very important. Vitamin D also has that great little quality of being an antioxidant like I mentioned above and helps to knock out nasty free-radicals in fatty tissues. Despite your thoughts about your belly fat not mattering if the free radicals invade, you do actually have some very important fatty tissue like the insulation around your nerves (called a myelin sheath), oh... and this little old thing called your brain! If free radicals get out of control (you mean get radical?) they can cause widespread destruction of your DNA which... you guessed it, leads to cancer! So keeping them in check is definitely a good idea.
Oh yeah! Vitamin D also helps to regulate the production of a protein in your body called cathelicidin. This protein is part of your body's innate immune system which is the first part of your immune system to get activated any time you have an infection. It helps to "nip it in the bud" as they say. Having adequate Vitamin D helps ensure that your body is ready and armed to fight the bugs, be they bacteria or be they viral.
So, in summary: Vitamin D is made beginning with a reaction triggered by the sun. It is naturally found in fat (and is commonly supplemented into dairy and other foods) and meat to some degree. It has some very important functions in your body (remember the receptor is found on virtually every cell in your body!) and protects you against all sorts of nasty cancers, autoimmune diseases, helps support your bones and teeth, and helps your immune system be ready to fight. You cannot get adequate vitamin D in the winter months in the US (unless you live in Florida or Hawaii- call me I need a sunny vacation!) and supplementation is generally recommended (always good to get your values checked to see how much is needed). The current recommended daily allowance was raised in 2010 to 600 IU for pretty much everyone (special rates for those under 1 and over 70). Since it's winter up here in Oregon and trying to snow I will be including my vitamin D in my regimen today and every day until the sun comes back in the spring.... ahhh.... daydreams of sun.... and Vitamin D!
One last note! I forgot to talk about D2 vs D3. Vitamin D2 is a molecule called ergocholecalciferol which your body can then convert into cholecalciferol, but only does so at about 33% efficiency, so it's considered 1/3 as bioactive as D3 which is straight cholecalciferol ready to go to your liver. D2 is often the form that will be naturally occurring in dairy products as it is made when hay is left to dry in the sun, then the cows eat the hay, and magic! Vitamin D enhanced dairy! The downside, other than the poor bioavailability is that it is much easier to build up toxic levels of supplemented vitamin D2, hence why you rarely see it marketed as a supplement any more.
Here are a couple references from which I pulled some of this information:
The Huffington Post (huffingtonpost.com) - Vitamin D Might Protect Against Tooth Decay: Study -By Annie Hauser - (Friday, December 07, 2012) -
The Wall Street Journal (wsj.com) - Multiple Sclerosis Linked to Vitamin D Levels, Study Says -By Jennifer Corbett Dooren - (Monday, November 19, 2012)
Vit. D and Diabetes type I
Vitamin D and Cancer
I also included information I learned last summer in my Integrative Oncology Research Course and the basic biochem came right out of my biochem lecture on Vitamins from last year.