What You Need to Know: After age 50, your stomach secretes less acid to break down and absorb vitamin B12, so compensating for what you're losing can be important. Recent research suggests a diet rich in B12 lowers the risk of developing Alzheimer's disease, but it's unclear whether taking a pill may have the same effect. Since B12 is needed for cell replication, DNA and blood cell production, B12 deficiency is associated with fatigue.
Who Should Take It: Vegans, people with gastrointestinal disorders and those with pernicious anemia, an autoimmune disease.
What to Watch Out For: Aspirin, certain antibiotics, oral contraceptives and acid-blocking medications like Nexium and Prilosec can interfere with B12 absorption.
Get It Naturally: Poultry, eggs, clams, fish and meat are rich sources, as are fortified breads and cereals.