Thursday, May 20, 2010

Sunshine of Your Love Part 2: The D Factor

Sunshining sea lion soaking up some vitamin D.

This is the second installment in our series about the sun.  For context, please read Sunshine of Your Love Part 1: Safely Getting What You Need.

So today, let's talk vitamin D.  We all know about vitamin D.  It's in the milk ads, in the news, and in steadfast nutritional pillars of our society: breakfast cereal, milk, margarine, and orange juice.  According to The Washington Post:
Vitamin D is shaping up to be the nutrient of the year, if not the decade.
This vitamin is common dinner table and water cooler conversation.  When the sun kisses your face, you likely think of it and then think of sunburn.  Vitamin D is the puffy white cotton candy cloud top, while it's alter ego, sunburn, is the thunderous underbelly, a raging tempest.  And with such mixed consensus about the sun, fortified foods, and supplementation, vitamin D sits right in the middle, teetering on the seesaw between nourishment and harm.

There are a lot of questions about vitamin D and today is it's time in the sun ;)

1.  What is it?

Short answer: a fat soluble, essential vitamin that acts as a hormone.

2.  Why do you need it?

Short answer: it has a multitude of roles to play and protects against cancer.

3.  Where do you get it?

Short answer: from the sun on your skin, from certain foods with animal origin, and from supplementation.  But whether or not any of these sources alone can meet your needs requires further discussion.

Now for the elaboration.  Why?  I don't want to provide Just Because kinds of answers--I want you to learn something and understand it so that you can discuss the subject intelligently.  For example, how do you respond when someone says that they get all the vitamin D they need from their fortified skim milk and from their sunscreen-lathered sunbathing?  Curious?  Read on.

What is Vitamin D?

Vitamin D is classified as a vitamin, but also as a hormone, or "pro-hormone," since it is synthesized by body tissues like a hormone as well as ingested through the diet like most other vitamins.  As a hormone, vitamin D regulates growth, development, and metabolism, whereas most other vitamins play bit parts in these processes.  Vitamin D enters the body either through synthesis in our skin cells or through foods (and supplements) we eat (for more see Where Do You Get Vitamin D? below).  Whatever the source, it must be transported to the liver where it is hydroxylated and circulated as hydroxyvitamin (which is the substance we measure to obtain vitamin D levels), called calcidiol.  Calcidiol is the storage form of vitamin D in your body and it is used to make calcitriol either in the kidneys or, if any is left over, directly in the cells.  This form enters cells and regulates gene expression.  As a hormone, vitamin D transports signals and messages; cells even have receptors for it just like they do for cortisol.  Hence, with vitamin D there is definitely more than meets the eye (did you say that in your mind with a robotic voice?  Yeah, I thought so :) ).  Vitamin D plays a host of roles, discussed in the next section.

Why Do You Need Vitamin D?

One of the most important jobs of vitamin D in the body is to maintain calcium levels.  It does this by reclaiming circulating calcium and increasing calcium absorption in the small intestine or, if dietary calcium is insufficient, by leaching calcium from the bones (ever hear of osteoporosis?).  That is why vitamin D and calcium fortification go together--you need adequate dietary calcium or vitamin D will get it by any means necessary.  This is a Clear and Present Danger sort of situation.  We'll go into just when this "no holds barred" presidential order is issued in a future installment on exactly how much vitamin D is adequate (that's a whole 'nother can of worms).  In addition to maintaining healthy bones, vitamin D also plays a role in insulin secretion, muscle health, metabolism, immunity, and blood pressure regulation.  Bottom line: it earns it's title as Essential.

An additional benefit of vitamin D is that it protects against cancer.  Vitamin D increases cellular differentiation, the specialization of cells to their specific functions, at the cost of decreasing cellular proliferation, the creation of new cells.  How does this relate to cancer?  Well, the chances of error (mutation) increase the more copies are made of any one thing.  Ever play the Telephone Game?  Then, you know of what I speak.  Cell proliferation increases the chance of mutation, thus, the formation of cancerous cells, a possible outcome of mutation.  Proliferation also makes matters worse once cancer cells are formed because it rapidly spreads them.  So the more vitamin D, the better your chance not to develop or to spread cancerous cells (to a point--we'll discuss toxicity concerns another day).  Interested in more about vitamin D's protective role?  Free the Animal summarized an incredible study on the Dose-Response of Vitamin D and a Mechanism for Prevention of Cancer.  Check out the charts to visualize it.

Without adequate vitamin D, infants and children can develop rickets, a bone growth impairment leading to deformity (softened bones bow out during development).  Surprisingly, even with vitamin D fortification of foods, rickets is still being reported in cities.  That is why our next section is so critical.  Other signs of deficiency are increased fractures, bone pain, and muscle pain and weakness.  Sounds fun!

Where Do You Get Vitamin D?

There are three main places to get vitamin D when you live paleo-style: one is through your skin, another through your food, and the third is through supplementation.  I would rather get my vitamin D from my skin and from whole foods, but there is debate about whether the sun or whole foods can supply us with the amount we need, thus, the need for supplementation.  Of course, if you eat processed foods, many are fortified with the vitamins and minerals you need despite the fact that the are ALSO full of everything you do NOT need, like ubiquitous grains, vegetable oils, sugars, and chemicals.  You can't make up for nutrient-poor foods, their constituent parts striped of any nutritional value during refining, by pumping them full of refined vitamins and minerals.  Processed foods do NOT do a body good.  In our evolutionary past, eating vitamin D-rich foods and spending ample time exposed to the sun allowed us to get what we needed, but in today's 9-5 world, getting sun is limited, and getting it from whole foods is difficult, if not impossible.

From The Sun

So how does your body synthesize vitamin D?  The ultraviolet radiation from the sun hits your skin in two main wavelengths: UVA and UVB (there is a third wavelength, UVC, that is mostly absorbed by the ozone and is actually given off by artificial lighting like fluorescent and halogen bulbs, so be wary).  UVA is the kind that penetrates into deep skin layers and creates free radicals.  According to the Weston Price Foundation's The Miracle of Vitamin D article, UVA leads to tanning, but not burning unless excessive, while UVB readily leads to burning (which is a flush of blood to the surface of the skin to repair damaged cells).  UVB also provides the necessary cue for our skin's production of vitamin D, but it too is harmful and can cause skin damage.

So how is vitamin D actually made?  UVB rays activate vitamin D synthesis by turning a certain cholesterol in our skin cells into cholecalciferol, or vitamin D3 (See? ALL cholesterol is NOT bad!  We make and need our own!).  Since the vitamin D needs to be absorbed from the oils on the surface of your skin, you shouldn't bathe or swim within one hour of sun exposure if you are trying to get your vitamin D primarily from the sun.  Thus, you need UVB to synthesize vitamin D in your skin, but not too much that you damage cells and increase your risk of skin cancer.  Talk about a balancing act!

What could make this even worse?  How about not only do you have to be careful not to burn, but the amount of vitamin D you can synthesize from the sun varies tremendously by time of day, time of year, latitude, age, skin exposure and duration, and skin color?  Let me explain.
  • Time of Day
UVB (the one leading to vitamin D AND sunburn AND skin cancer) is most intense at midday, but UVA (the tanning one that also contributes to skin cancer) is equally intense throughout the day--and both are even present on light cloudy days (hence my mom always telling me to wear sunscreen even when it's cloudy, which I thought was just being mean.  I think parents get a perverse enjoyment out of slathering sunscreen on wiggly children who pucker their faces with annoyance and can't believe the audacity of their parents to delay their play.  It's a ritual.).  So you have to get your vitamin D from sunbathing at midday, the time that ALSO puts you at the most risk.  Great.
  • Latitude and Time of Year
The further you are from equatorial regions, the less intense the UVB rays.  You need a UV index of 3 or more to kickstart your vitamin D synthesis, and while that is daily in the tropics, it's only daily in the the spring and summer in temperate regions, and almost never in the arctic.  According to Weston Price Foundation's article on The Miracle of Vitamin D:
Latitude and altitude determine the intensity of UV light. UV-B is stronger at higher altitudes. Latitudes higher than 30° (both north and south) have insufficient UV-B sunlight two to six months of the year, even at midday. Latitudes higher than 40° have insufficient sunlight to achieve optimum levels of D during six to eight months of the year. In much of the US, which is between 30° and 45° latitude, six months or more during each year have insufficient UV-B sunlight to produce optimal D levels. In far northern or southern locations, latitudes 45° and higher, even summer sun is too weak to provide optimum levels of vitamin D. 
  • Age
The older you are, the less efficient your vitamin D synthesis, so you need to stay in the sun longer to generate vitamin D.  But older skin is also more susceptible to burning, so it's a wash.
  • Skin Exposure and Duration
Weston Price Foundation's article on The Miracle of Vitamin D says that the current prescription of 10 minutes of midday sun exposure a day is not enough.  And remember, you can't wash your skin, bathe, or swim for at least an hour if you want to absorb that vitamin D.  
The current suggested exposure of hands, face and arms for 10-20 minutes, three times a week, provides only 200-400 IU of vitamin D each time or an average of 100-200 IU per day during the summer months. In order to achieve optimal levels of vitamin D, 85 percent of body surface needs exposure to prime midday sun. (About 100-200 IU of vitamin D is produced for each 5 percent of body surface exposed, we want 4,000 iu.) Light skinned people need 10-20 minutes of exposure while dark skinned people need 90-120 minutes.
  • Skin Color
 The lighter your pigmentation, the more quickly you'll burn.  We'll discuss this more in our final chapter:

Hey Chorles?  

Okay, Chucky D, so if the sun KILLS us, how the hell did we survive this long?  If it is that dangerous, wouldn't our ancestors all have had skin cancer and never have survived?  The evolutionary answer is skin pigmentation.  Melanin, the pigment in the skin, protects us by absorbing UV rays and disbursing them as harmless heat.  The more melanin, the darker the skin, and the more UV protection.  However, this UV protection comes at the cost of less vitamin D synthesis since it relies upon those UV rays to kickstart the process.  Accordingly, the distribution of skin pigmentation before modern transportation generally followed latitude: darker where the sun is brighter to protect the skin from the more intense rays, lighter where the sun is less bright and more intermittent, so that any sun exposure can get vitamin D synthesis activated post-haste.  Tanning is a second defense and one that depends on environmental cues.  It can be both adaptive and detrimental.  When UV rays damage your skin, they trigger more production of melanin to protect it from further assault.  So while it is a good thing to have more melanin to protect your skin if you are often out in the sun, also keep in mind that tanning shows damage already done and slows vitamin D synthesis, since the melanin is absorbing the UV before it can activate vitamin D synthesis.  See, even the biological world lives in shades of grey and defies a good/bad dichotomy.     

It's a trade-off: the evolution of darker skin pigmentation around equatorial regions allowed for more sun exposure before burning, but resulted in slower vitamin D production and required longer duration of exposure.  And vice versa: lighter skin pigmentation evolved farther from the equator to allow for quick vitamin D synthesis where there was reduced solar intensity, but came with the cost of greater susceptibility to sunburn.  You're damned if you do and if you don't.  Interestingly, there are a few exceptions to the generality, such as the Eskimo, who have darker skin than expected at such a sunlight-poor latitude.  How were they not vitamin D deficient?  Fish.  They ate lots of fish, which have the vitamin D they needed to survive.  

While skin pigment gradation by latitude was once useful, since we have migrated, it has become an issue.  Today, those with darker pigmentation are more likely to be vitamin D deficient without ample sun exposure, which is difficult to achieve at any latitude in today's working 9-5 world.  Between melanin levels, all the factors associated with sun exposure, and our prodigious use of sunscreen, it is highly unlikely that we are meeting our vitamin D needs through the sun alone.

All of these confounding factors add up, which is why many are deficient even in sun-soaked regions.  This study from sunny Florida, and this one from Hawaii show that even where there is adequate sunlight, people are still deficient.  So we're still left with the question: where can we get the vitamin D we need?

And that, my friends, is a tale for another day.  This story is NOT over yet!

Here is our next installment: Sunshine of Your Love Part 3: What is e-D-ible?


General references used extensively:
Micronutrient Information Center at the Linus Pauling Institute of Oregon State University
The World's Healthiest Foods: Vitamin D
Weston Price Foundation's article: The Miracle of Vitamin D
The Vitamin D Council, especially vitamin D physiology
Ultraviolet Radiation from The University of Minnesota School of Public Health
Wikipedia entries on Vitamin D and Melanin and Ultraviolet

1 comment:

  1. Hey K,

    As I mentioned on facebook, Great job! Even residents here in AZ don't fully understand how to get the proper vitamin D. Thanks and can't wait for your next mini series. Jo