Well, to me it sounds like arsenic. Which is available in drinking water, and sometimes in ordinary food (like salads, etc.). Pesticides. Playground equipment and other 'weather treated' wood. Some medications, believe it or not. It's odorless, tasteless, etc.

Here is an old description. But good descriptions are hard to find, so please consider reading this:

http://www.pubmedcentral.nih.gov/pic...4&blobtype=pdf

It's a .pdf file of a page -- it's necessary to scroll down about halfway, in order to find the title ("Chronic Arsenic Poisoning Masquerading as Pernicous Anemia").

Surely there are other possibilities, but check this one out . . . just in case.