Reading on wikipedia and Weston-Price about vitamin D it seems that
when we are exposed to sufficient levels of UVB the amount we get is
self regulating:

Exposure to sunlight for extended periods of time does not normally
cause vitamin D toxicity.[43] This is because within about 20 minutes
of ultraviolet exposure in light skinned individuals (3–6 times longer
for pigmented skin) the concentration of vitamin D precursors produced
in the skin reach an equilibrium, and any further vitamin D that is
produced is degraded.[49] Maximum endogenous production with full body
exposure to sunlight is 250 µg (10,000 IU) per day.[43] (Wikipedia)

Any ideas for how long we have been wearing clothing and/or living in
areas of the earth with lower UV B levels than our ancestors?

I take it a a given that living nearer the equator we would get more
UV B and therefore more opportunity to make vit D - provided of course
that our diet provided the materials for the necessary precursors. Pre
jeans and t-shirts etc - more exposed skin.

Cheers

Neil

PS I just made my first bone broth - had a couple of marrow bones left
after eating the marrow and wondered what to do with them - far easier
to make broth than I thought in a slow cooker - tastes really good:-)

On Mon, Sep 7, 2009 at 11:00 PM, Elizabeth
Beasley<[log in to unmask]> wrote:
> I have a question. Since we can test Vitamin D levels in people today, and
> they can come out low, how do we know what our ancestor's levels were,
> because of course we didn't have the technology back then. How do we know
> what is "optimal" for vitamin D levels? Is it possible that our ancestors
> got lots of sun, but still had low vitamin D levels as well?
>
> --Elizabeth

-- 
Neil C Timms