Similar to blood pressure and fasting glucose, the Vitamin D levels in your blood are one of the more relevant markers of overall health.
Since the federal government required milk to contain vitamin D decades ago (about 100 IU per eight ounces), to cure widespread rickets in the cities and countrysides, this nutrient has been viewed as an important ingredient of bone health.
It's not a magic bullet, but the latest research has shown that the active form of vitamin D is also crucial for overall immunity, chronic-disease prevention, and healthy aging.
Here's a handy page discussing the role of vitamin D in preventing several medical conditions.
For just one example from the latter page, let's look at the lethal condition called pancreatic cancer, which has cut down Steve Jobs, Patrick Swayze, and hundreds of thousands of others.
Several studies have researched solar ultraviolet-B (UVB) light, vitamin D, and pancreatic cancer.
There was a lower incidence and death rate from pancreatic cancer in people exposed to higher levels of solar UVB light. These studies appear to be reliable and accurate. They researched the effects of UVB light during an entire lifetime. There have been similar results in Japan and the United States.
People who live in warm, sunny climates produce adequate levels of vitamin D. They have a higher risk of nonmelanoma skin cancer. But they have a lower risk of pancreatic cancer.
Getting your D-levels into the sweet spot (see below) is yet another way you can tweak your health in the right direction. For some people, it might be a life saver.
My own hacking experience is a pretty typical one.
The body creates as much vitamin D as it needs via a chemical reaction on the skin with UVB rays from the sun. You cannot generate too much vitamin D from the sun, although you can supplement to levels that eventually become toxic (albeit, these are extreme levels to absorb, in the realm of well over 20,000 IU per day).
As a fat-soluble vitamin, the biochemical is stored in the body fat, so you could potentially sock away too much of it. For the vast majority of people, this is not an issue.
This summer, I was trying to find out whether I could generate enough vitamin D naturally from the sun alone.
This is how we're designed, ultimately, to make enough vitamin D for the body's needs. Some evolutionary anthropologists have theorized that skin became lighter as humans migrated north from Africa, in order to permit the absorption of more UVB rays at higher latitudes, to generate adequate vitamin D.
Testing Your Own D Levels
Testing for vitamin D yourself is reasonably acurate and very easy to accomplish: prick the tip of your finger, leave a few bloodspots on a pad, and send the kit back to the lab. Then check out your level on a web site about two weeks after the test. I use ZRT lab in Oregon, USA.
Optimal vitamin D levels are still the subject of debate, although it's safe to say that you want your levels to be greater than about 30-40 ng/ml (nanograms/milliliter).
One study of healthy ancestral peoples who farm and hunt-gather outdoors found that they have mean vitamin D levels of about 44-48 ng/ml, and I've settled on that level as optimal. (See Chapter 4, page 96 of Fitness For Geeks.)
I tested my levels during the spring of 2013 after supplementing, and found they were about 35 ng/ml. How much could I generate with just sunlight, during the Summer months in New England (plus two weeks in Kauai), to bump that up to the forties?
Can I Hack It With Sunlight?
I completely went off supplements and undertook some pleasurable and strategic sun exposure, meaning I got what I took to be healthy doses, stayed away from sunscreen, and often maintained a light tan. This went on for about two months. Then I tested again. This time my blood levels had actually dropped to 31 ng/ml, which is borderline deficient.
I can only speculate why. Possibly my age (56) prevents me from efficiently generating enough vitamin D from the sun. "Youth challenged" people apparently can't convert D in the skin to active form as well as the youngbloods.
Maybe my physical activity level, which is high, has shunted high levels of the vitamin's active form from the bloodstream to the cells, where it's used to combat inflammation? I don't know, but I concluded I had to go back on to the vitamin-D supplement wagon, which meant taking anywhere from 2,000 IU to 4,000 IU per day, in gel-cap form.
So that's what I did for another six weeks or so.
The only way to figure out what works is to test again after a month or two, which I did (I didn't feel any different either way, by the way). I got the results a few weeks ago: 50 ng/ml. This is right around where I want to be, so I was pleased with those results.
It seems that I personally require a combination of sun and supplements. Heading into the Vermont winter, I will no doubt test again soon. Additionally, I don't want to move above 50 ng/ml, although the testing organizations often recommend a level between 50 and 80 ng/ml.
More info on testing and optimal levels: http://www.vitamindcouncil.org/about-vitamin-d/testing-for-vitamin-d/.
For the science and detailed information on vitamin D: Chapter 4 of Fitness For Geeks.