--in some amounts in body fat.

Since Vitamin D is made in skin through sunlight activation, it can be classified as a hormone, but for convention's sake we still generally talk about it as a vitamin.

What is really stored in large amounts is the Vitamin D precursor--calciferol-- that is activated by sunlight. There is a complicated feedback mechansim that shuts off the D-production process from calciferol after about 20-30 minutes of direct sunlight--just about the time most people of mid-range complexions start to pink (this reddening is a direct indicator the body has absorbed enough ultraviolet light for the manufacturing of D--exposure BEYOND that gets more dangerous as regards skin cancers). In fact, many experts are now saying that people should absolutely be getting more sun exposure than they've been, as direct sun exposure is hard to come by except for people in low latitudes during noontime (people who have evolved in such places have darker skin to keep this balance--in fact, pale skin is considered a benevolent mutation to allow people at higher latitudes to make more Vitamin D), especially during winter months.

It does seem as if our tendency to stay indoors, slather on sunscreen, and not update the minimum daily requirements for dietary ingestion of Vitamin D in such circumstances is contributing to a very large number of D-deficienct people in the developed world.

Ted Hutchinson over at Braintalk has ammassed an enormous database of material--studies, monogarphs, clinical reports--to this effect, analagous to what Cara (jccglutenfree) has done with gluten:

http://brain.hastypastry.net/forums/...ead.php?t=2822

(I've got to see if I can get him to post over here--there was a bit of controversy when he tried some time ago--perhaps a talk with the Mods . . .)

One of the most important things it reveals is that our supplements should be the much more efficient bodily-produced D3 (cholecalciferol) form rather than the synthetic D2 (ergocalciferol) available at most stores. This situation is reminiscent of the cyanocobalamin/methylcobalamin contrast with B12. (D3 is now becoming increasingly available.)