Vitamin D: Sun Exposure, Supplementation and Doses

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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.

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