I don't know but 20's is not looking too good from where I am at. It is hard thinking I have to live in pain like this till I am 80. Anyhow remember my b12was 2000 and my doc told me to stop too. Actually it was 1500 and then when I stopped it went to 2000. I feel blood work is often off. When I was ill I had bloodwork almost everyday and every day it changed. I guess for me I follow my docs. Not so much cause I think their right but more because when I feel worse or something happens they can't blame it on something I did. It is like for my car I always keep reciepts so when they try to blame the problem on me I have proof.