><< BTW I generally refuse to use the term "vitamin C"; "ascorbate" is
> also a bit narrow but at least it doesn't group this remarkable
> substance with the "true" vitamins. >>
>
>What is your definition of 'vitamin' that excludes C?

I would not contradict any "official" definition of
"vitamin", but a very rough definition might refer
to organic trace nutrients found in foodstuffs
that are not produced exogenously and must be consumed
regularly to support growth and metabolic processes.
Under this set of criteria I suppose cholecalciferol
("vitamin D"), being produced endogenously under
exposure to the UV in sunlight, is arguably not
a vitamin, unless babies receiving it in mother's
milk is considered.

With this admittedly broad definition in mind, consider
the goat: ascorbate is not a vitamin for this animal
because it produces it in its liver. The same goes
for practically all other animals. Further, ascorbate
is generated in greater or less amounts, responding to
stresses, injuries etc.

The point is that, but for a genetic mutation in
the past, mankind would have no use for ascorbate
as a vitamin, except maybe as an adjunct in compensating
for extraordinary stresses.

It's also different in that it is nontoxic, unlike
most if not all of the "true" vitamins past a certain
dosage. It plays a role in a huge number of bodily
processes, unlike many "true" vitamins that participate
at only key points.

Anyway, this is only a start, and the relevancy of this
discussion is marginal on a paleo list. A websearch for
the papers of Irwin Stone would find more eloquent and
complete discussion of ascorbate.