Wow. I just got my vitamin D level tested, and it was only 19 ng/ml 
(47.5 nmol/L?). That's below even the minimum level to prevent 
rickets, and way below the levels needed to prevent cancer, 
osteoporosis, depression, heart disease, chronic pain & fatigue, 
hypertension, influenza, and more. And that's for a white guy at the 
end of summer, after a week at the beach in a bathing suit without 
much sunscreen (just a few critical areas--did get a tan line), and 
one who eats a "paleo" diet with a fair amount of Alaskan salmon and 
eggs and meat. As a white guy who's not afraid of the sun and spends 
some time outdoors, I thought I would be storing up D for the winter. 
But they say you don't store it until your levels are above 50. The 
old "fifteen minutes a day on your face and hands" is a recipe for 
dangerous loss of health. Working against my D levels, as I see it, 
are my latitude (44N), cool climate (Vermont), thick ozone layer and 
industrial pollution in the Northeast, age (51), and amount of time 
spent indoors and in cars.

We are really evolved, or calibrated, for a life spent outdoors all 
day, every day, without lots of clothing, except when it's cold. I 
don't see any way to get healthy levels of D without supplements. The 
amounts of D I see in foods don't seem adequate, and certainly didn't 
work for me. Unless you eat a true, traditional Inuit diet (which is 
why they can be healthy with a somewhat dark skin tone at such a high 
latitude).

Vitamin D is probably by far the most important supplement you could 
take, and most people these days are dangerously deficient. Probably 
even people on this list who think they're not at risk. I thought I 
wasn't, until I finally got the test.

I'm urging family and friends to get their D levels tested, or to 
start taking 10,000 i.u. per day. It has to be D3, or cholecalciferol. 
I bought a bottle of D pills of a good dose for my kids, and didn't 
notice until I had opened it that it was ergocalciferol. Had to throw 
it out. If you get that much D from cod liver oil, that may give you 
too much A, which competes with D and can cause bone loss.

Here are two fascinating videos on vitamin D and micro-Darwinian 
carcinogenesis:
http://www.youtube.com/watch?v=3GM0CnO6-ds
http://www.youtube.com/watch?v=1PsyaYNX1dw
And there's a lot of good information on dosages, toxicity issues, and 
cheap(ish) home testing, at www.vitamindcouncil.org

Hilary