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More information Benefits and uses of B-complex vitamins Medically reviewed by Alan Carter, PharmD on April 2, 2019 — Written by Jennifer Berry Vitamin B complex Dosage Benefits and uses Who should take them? Side effects and risks Choosing supplements Interactions Foods Summary If you buy something through a link on this page, we may earn a small commission. How this works. Vitamin B refers to not one, but eight different vitamins. All B vitamins play a role in converting food into energy in the body. Each vitamin also has a unique role in a person’s health. Vitamin B-complex supplements include all of the essential B vitamins in one pill. Some contain 100 percent of the recommended daily allowance (RDA) of every B vitamin. Others contain higher doses of some or all of these vitamins. Many people get all the vitamin B they need from a varied, healthful diet, but others benefit from taking a vitamin B-complex supplement.