Lammie,
if you try the "search" function on top of this page and look up "supplements" you'll find tons of interesting threads on the matter. It's been thoroughly discussed in the past.

(Make sure to make your search in "advanced mode" and tick "search titles only". Otherwise you'll get tons of hits on peoples journals.)

You might also want to take a look at the "Low Carb Health & Technical Forums" (on the main page) where there is a subforum called "Nutrition & Supplements".

Cheers!

/gil