Cyano is synthetic and some people cannot convert it to the active methyl form.

So since the methyl is now available inexpensively, one can skip the old form and use the more helpful methyl one.

This is the table from the study that actually measured B12 after dosing:

http://www.ncbi.nlm.nih.gov/pmc/arti...able/T1/#TF1-4

500mcg is tolerable but not as good as 1000mcg. You would probably pay the same for both. So why not have the best?

This is the B12 informational thread:
http://neurotalk.psychcentral.com/thread85103.html

Transcobalamin is a rather new topic...and little research has been done on it. It is thought to be a genetic error, like the MTHFR problems. The whole oral B12 thing is very new too.
Most of the studies just measure patient response, and do not go into the bioavailability etc., since it is expensive to do so.
And many doctors don't even know what methylB12 is.

I have read that it might be possible to flood the GI tract and get passive absorption and results even if transcobalamin is defective. Hence the high doses would work this way.

But this is still pretty rare, and not germane to most of the users on this forum who just want to speed brain healing.

There are many forums on the net who get into endless discussions on the factoids of B12 therapy now. It is really confusing and I believe for the most part, the general public is not really going to accept all of that. So best to just start logically and see what happens. Estimates today are that about 40% of people in this country are needing B12 supplements ....the reasons can be many, and some very rare.