B12 is important to every cell and system, including the blood and nervous system. B12 and other B vitamins (folate and B62) may help prevent heart disease by lowering blood levels of homocysteine, a substance linked to heart disease, though this is theoretical. B12 is found naturally only in foods of animal origin; many other foods are fortified with it. The body can store large amounts.

Claims, purported benefits: B12 prevents confusion and memory loss in older people, protects the heart, peps you up, especially when given as injections.

Bottom line: Many people over age 50 don’t produce enough stomach acid to adequately absorb B12. A poor diet and heavy drinking can also contribute to a deficiency. Vegans (who eat no animal products) and people with intestinal diseases can also be at risk. Severe B12 deficiency can cause confusion, memory loss, tingling and weakness in the limbs, hallucinations, and listlessness. A much rarer but more serious type of B12 deficiency that can occur at any age is pernicious anemia, in which the stomach nearly stops producing acid and a protein also needed for absorption (intrinsic factor), so that virtually no B12 from food is absorbed. Initially this causes anemia, but eventually, when B12 stores are depleted, there can be irreversible damage to the nervous system. Blood tests can diagnose a B12 deficiency; high doses of B12 can correct it. Older people need 6 to 15 micrograms of B12 daily (the RDA is just 2.4 micrograms), easily obtained from food and a multivitamin. Most multis marketed for seniors have 25 or 30 micrograms. If you are over 50, talk to your doctor about having your B12 level measured.