"high levels of folic acid may exacerbate the neurological consequences of a vitamin B12 deficiency"
Folate and brain function in the elderly
My Mum had a B12 level that was in normal range but still below the 400 where I think its worth a trial of B12 needles(349), and high (above range) red blood cell (RBC) folate. This is folic acid.
My levels in blood were similar: RBC folate above range, B12 345.
When she was repeatedly telling me the same story and forgetful,
she responded well to a few ( about 4 to 6 over a few months) B12 injections. The injections were hydrocobalamin (in Australia).
After this I could hold a conversation with her again.
The following on folate transporters (FOLATE as well as Thiamin ):
http://tealady-health.blog.co.uk/2006/09/09/thiamin_transporters~1110229
http://tealady-health.blog.co.uk/2006/09/09/thiamin_transporters~1111873
technical ..
Mum and I both test as above normal range RBC folate.. but I couldn't see any implications of this from these studies.. other than that the serum folate may still be normal.