Hi Tom,
I went looking for info on the B12 study which made a possible link of high b12 to prostate cancer and it's amazing how much conflicting data is out there. There are so many variables that, for me at least, I would be hard pressed to accept the data based on one study. Many of our foods are fortified with B12 and folate and it is with the type requiring conversion by the liver. There are new metabolic disorders that have been identified in the past 8 years in which some people cannot convert certain forms of B1, B12 and folate to a form usable by the body. It then stays in the blood, creating a false, elevated level.
There are various forms of B12, cynocobalamin, methylcobalamin, adenocobalamin. The methyl is bio-active and does not require conversion by the liver.
The next time you get your B12 checked, also have them check your MMA and homocystiene levels. These are a better indication and will further help you determine your B12 status. See the link below.
http://www.aafp.org/afp/2003/0301/p979.html