The human body needs vitamin B12 to make red blood cells, nerves, DNA, and carry out other functions. The average adult should get 2.4 micrograms a day. Like most vitamins, B12 can’t be made by the body. Instead, it must be gotten from food or supplements. And therein lies the problem: Some people don’t consume enough vitamin B12 to meet their needs, while others can’t absorb enough, no matter how much they take in. As a result, vitamin B12 deficiency is relatively common, especially among older people. The National Health and Nutrition Examination Survey estimated that 3.2% of adults over age 50 have a seriously low B12 level, and up to 20% may have a borderline vitamin B12 deficiency. A serious vitamin B12 deficiency can be corrected two ways: weekly shots of vitamin B12 or daily high-dose B12 pills. A mild B12 deficiency can be corrected with a standard multivitamin. In many people, a vitamin B12 deficiency can be prevented. If you are a strict vegetarian or vegan, it’s important to eat breads, cereals, or other grains that have been fortified with vitamin B12, or take a daily supplement. A standard multivitamin delivers 6 micrograms, more than enough to cover the average body’s daily need. If you are over age 50, the Institute of Medicine recommends that you get extra B12 from a supplement, since you may not be able to absorb enough of the vitamin through foods. A standard multivitamin should do the trick.