" But even meat-eaters can run low in vitamin B12, because they may not absorb it adequately. That is especially true if they are over fifty, do not produce enough stomach acid, or take acid-suppressing medications or metformin, a common diabetes drug. As a result, health authorities recommend that everyone over age fifty take a B12 supplement or use B12 -fortified foods. This is actually good advice for everyone, no matter what your age. And a B12 supplement is essential for anyone on a vegan diet. "

― Neal D. Barnard , Your Body in Balance: The New Science of Food, Hormones, and Health