title: I take vitamin B₁₂supplements daily, but blood tests show that I have a deficiency.  How is this possible?
mesh_terms: D000367:Age Factors; D019587:Dietary Supplements; D015438:Health Behavior; D006304:Health Status; D006801:Humans; D008875:Middle Aged; D014805:Vitamin B 12 / Q000008:administration & dosage* / Q000493:pharmacokinetics; D014806:Vitamin B 12 Deficiency / Q000097:blood / Q000175:diagnosis / Q000188:drug therapy / Q000517:prevention & control*; D014803:Vitamin B Complex / Q000008:administration & dosage* / Q000493:pharmacokinetics
chemical_list: D014803:Vitamin B Complex; D014805:Vitamin B 12