Related: What Happens to Your Body When You Take B-Complex Vitamins Regularly ... There are several forms of B12 including adenosylcobalamin, methylcobalamin and hydroxycobalamin.

Dear Doctors: I was surprised when a blood test at my annual checkup found I’m low in B vitamins, especially B12. My doctor gave me a shot, and the fatigue that I had been feeling went away. Why is ...