From the presence of vitamin D receptors in our cells and vitamin D factories in our epidermis, along with the central role vitamin D plays in calcium metabolism, immunity, and gene expression , it’s pretty clear that having adequate vitamin D is an essential component of being a healthy, successful homo sapien. And yet, many health practitioners suggest that vitamin D deficiency is one of the biggest nutrient deficiencies in modern society. The question, then, arises: What’s the best way to get enough vitamin D – via oral supplementation or sunlight?
To determine that, let’s examine a few common questions surrounding the various modes of intake.
Is it natural?
This is a big one. We obviously care about how nature shaped human evolution. Shouldn’t then our mode of obtaining vitamin D also be “natural”?
For us humans, getting vitamin D from sunlight is the clear winner if judged by this standard alone. We are basically hairless, upright apes for a reason, with hefty D3 requirements, and before oral supplements appeared, dietary vitamin D was not a very reliable source. We had to get it from the sun. Today, we’re still those same hairless, upright apes (albeit with different fashion trends and hygiene sensibilities), and we can still obtain vitamin D from UV-B radiation. Personally, I prefer getting my D3 from sunlight, simply because it’s enjoyable to spend time in the sun and it’s an effortless way to get something that’s critical to my health. But I don’t think it’s necessarily “better” than getting it through supplements. Nature’s way is quite often better, or at least more congruent with how we’re “intended” to work, but that doesn’t always preclude the effectiveness of modern methods.
Additionally, as a little added factoid, this is essentially the way fur-bearing mammals and birds obtain the bulk of their D3: orally. The oils in their fur/feathers produce D3, and preening/self-grooming results in oral intake, with diet rounding out the rest. Skin production is either inadequate or nonexistent. Now, we aren’t dogs or sparrows, but the mechanism for oral intake clearly exists across a wide variation of species.
Yet another question arises: Does oral D3 differ – qualitatively – from solar D3?
Let’s examine the pathways – let’s see what happens when you produce or swallow vitamin D3.
When UV-B reacts with the 7-Dehydrocholesterol in your skin, cholecalciferol (D3) is produced and ends up in your liver, where it’s hydroxilated into calcidiol, also known as 25-hydroxyvitamin D or 25(OH)D.
When you swallow cholecalciferol (either in food or supplement), it ends up in your liver, where it’s hydroxilated into calcidiol, also known as 25-hydroxyvitamin D or 25(OH)D.
From that point onward, it’s all the same. It’s all calcidiol, ready for storage in fat tissue or dispersal to the kidneys for conversion into calcitriol, also known as 1,25(OH)D. Calcitriol is the active hormonal form whose primary role is to regulate blood calcium levels. If there’s enough calcidiol left in the tank after the calcium duties, it gets sent to other tissues in the body to be converted into more calcitriol to fulfill even more roles. That’s where all the immune system/cancer cell/heart health/insulin sensitivity benefits begin to kick in, and it explains why having plenty of vitamin D available – beyond what’s only required to avoid rickets and monitor blood calcium – is so beneficial.
Both oral supplements/dietary sources and sunlight can get you there. Qualitatively, they are identical. The only difference is in the dosage. With oral D3, dosage can be consciously controlled, but it’s also subject to human error (or foolishness). You could conceivably keep popping capsule after capsule and end up with toxic blood levels. It’s difficult to do (one official site  suggests the level might be in the millions of IUs), but it’s technically possible. When you sunbathe, on the other hand, you don’t consciously flip a mental switch that shuts down D3 production. Instead, you burn, or you grow uncomfortably hot. You – quite naturally – opt out of sun exposure before it gets too intense. As your skin darkens and you begin to tan, it produces less vitamin D, and you can stay out longer without burning, but it’s generally true that sun exposure up to the brink of turning pink is safe and will net you plenty of D3. In addition, it’s interesting to note that once you have produced enough vitamin D through sun exposure, those same UVB rays will begin to prevent excess vitamin D production by degrading existing cholecalciferol. Ain’t homeostasis grand?
So – sun or supplement? What should I do?
Take stock of your living situation. If the sun is available regularly where you live, go that route whenever possible. It’s free, it’s safe, it’s easy, and it’s enjoyable. Avoid burning, of course, and you’ll be safe. I find it inconceivable that the amount of sun exposure necessary to produce 10,000 IU of D3 (about 20-30 minutes of afternoon sun for light skinned folks; a few times that for dark skinned folks) will also kill you and give you skin cancer.
As with anything, though, ease into the sun. The pasty, mostly interior set will want to treat full sunbathing like learning to barefoot  sprint after a lifetime of dress shoes – they’re coming from a position of weakness, of sheltered living. Five minutes of unfiltered rays can turn a freckled redhead lobster-pink, sore, and resigned to indoor living. Just be careful. Ease into things. Learn your limits, and throw on a shirt or find some shade before you burn.
Eating the right foods seems to confer greater natural skin protection against the sun, at least anecdotally. I’m not exactly the best case subject to determine this, as I’ve spent much of my life fairly tan with regular sun exposure, but you hear time and time again about folks who cut the grains , sugar , and industrial vegetable oils , replaced them with veggies , meat , and animal fats , and have never had any issues with the sun again. Nutritional deficiencies do have the tendency to potentiate existing problems or jumpstart/trigger health maladies, so I wouldn’t be surprised. Besides, we’re eating this way regardless. We might as well pick up a few additional theoretical health benefits along the way.
We can’t all bask in the midday sun (if such a thing even exists in our neck of the woods), nor can we even reliably count on there being adequate sunlight on a regular basis. For those of us unable to run shirtless and shoeless through a sun kissed meadow, the last of its residual morning dew having finally evaporated, from noon to 12:45, our option is oral intake.
Certain foods get touted as vitamin D powerhouses: wild salmon , mackerel, herring, cat fish, cod liver oil, eggs . Eat these, but don’t expect to increase your 25(OH)D levels much. Don’t eat the fortified, processed junk which, in the case of cereal grains, actually reduces calcium absorption. It’s a good thing they’re usually fortified with meager amounts of vitamin D, just enough to avoid rickets and keep blood calcium relatively under control. Remember, the body preferentially uses available D for calcium regulation, so it’ll mobilize every last scrap when it comes to matters of the bones – but that is far from optimal. When you eat grains and other junk, you’re increasing your D requirements.
No, food will help, but it won’t suffice. You need something stronger. Might I suggest licking the nearest sunbathing dog? (Would that actually work? I know that most vitamin D3 supplements are isolated and extracted from the fat in lamb’s wool; perhaps a similar concoction could be devised from oily dog fur).
In all seriousness, take a good D3 supplement if you can’t get real sunlight. As long as you don’t go overboard on the dosage, you’re good to go. If it’s not in an oil-based capsule, just take it with a bit of fatty food (not a stretch for an Primal eater). It travels the same pathway and results in the same benefits. It’s always easier to just let nature take its course, but it’s not always realistic.
A good general rule is 4000 IU per day supplemented. That’s what I take during winter time and when I go a few days trapped indoors and without sun (as I was last weekend while at the Book Expo of America in New York). Get your 25(OH)D levels tested before you start supplementation, take the 4k IU daily, and get them tested again after two months. Aim to get your levels up around 50-60 ng/mL, which is where most of the big benefits  seem to kick in. If you don’t respond well to 4000 IU, feel free to increase the dosage. Given that we can make around 10,000 IU in well under an hour, supplementation up to that level is well tolerated.
I’ll end it here for now, with more coming tomorrow. It’s a big topic and there’s a lot to cover.