If you are supplementing with B12 and getting dismal results, I have come to find out, the hard way, that the FUT2 genetic polymorphism can affect your ability to absorb and STORE B12. Despite injecting TEN THOUSAND micrograms daily of hydroxycobolamin, my levels remained very low - with detrimental affects. After testing for the MTHFR polymorphism, the testing also revealed the FUT2 problem. Even many MTHFR specialists aren't 'in on" this aspect. The answer has been to DAILY inject large doses of B12 NOT cyanocobalamin - can lead to cobalt poisoning!!! I can "feel" my B12 levels lowering throughout the day - sort of like a personal "tank of gas". If I forget, my nervous system quickly reminds me to get with my B12 injection ASAP. It took MANY years for me to discover this - with resultant damage. I can not stress enough how important genetic testing can be for people with "weird" and unexplainable health issues!!
Lymerick