great question, to which I don't have a great answer. My local big grocery store (a Fred Meyer--owned by Kroger) has a health food/supplement section with a CD-rom data base that I use, and it has scientific references in footnotes, but I still get the sense that it promotes the use of supplements rather uncritically. They also have an encyclopedia of the sort you describe sitting there--it's probably a 800-page book, but I don't know the title!

Let us know if you find something good, especially if it seems balanced in its approach.