People underestimate the role of vitamin B12, and how difficult it may be to absorb, especially if someone has candida overgrowth, intestinal parasites, or insufficient stomach acid. In addition to being linked to ridges on the fingernails, anemia, and fatigue, B12 deficiency is linked to psychological problems as well. I recently realized how B12 deficient I am, and blame some of my most recent health problems on this. I am using a few sublingual B12 tablets a day. If they don't help enough, I might need to go for some B12 injections.