Very low, my husbands was at 189.00 and had him on a stroke ward for 24 hours , numerous hospital appointments almost having to retire early , and if I hadn't found out the cause for all his symptoms he would now be probably almost house if not bed bound .
I have been to a lecture on B12 deficiency and in range and optimal are two very different things levels below 500 are to low regards the central nervous system , and 1,000 is considered an optimal level.
If you are taking drugs such as omeprazole and some other drugs these inhibit the uptake of B12 , the best way to take B12 is sublingual under the tounge. GPs will mostly 🙄 at what I have said , as the teachings of B12 deficiency seem to have been forgotten in the teachings of the medical profession, unless they have an interest .
Also if you are vegatarian or vegan levels will potentially be lower , although shouldn't be if Roy war correctly .