By Lydia Nuzum When Dr. Hedda Haning started forgetting things, her daughter was the first to suggest she might have a vitamin deficiency. The 73-year-old retired anesthesiologist had not considered the culprit might be low levels of B12. When she was in medical school, they were taught to think of a lack of the vitamin only as a cause of pernicious anemia. Haning's B12 levels weren't particularly low when tested, either, but subsequent tests showed that her levels of methylmalonic acid were up, an indicator that she did have a B12 deficiency. Haning began taking B12 supplements nearly three months ago.