B vitamins are a class of water-soluble vitamins that play important roles in cell metabolism. Though these vitamins share similar names, research shows that they are chemically distinct vitamins that often coexist in the same foods. In general, dietary supplements containing all eight are referred to as a vitamin B complex. Individual B vitamin supplements are referred to by the specific name of each vitamin (e.g., B1, B2, B3 etc.). Each B vitamin is either a cofactor (generally a coenzyme) for key metabolic processes or is a precursor needed to make one. Because they are soluble in water, excess B vitamins (such as may be ingested via supplements) are generally readily excreted, although individual absorption, use and metabolism may vary. Most people acquire the necessary amounts easily in their diets with some exceptions. Vegans need supplementation for Vitamin B12. Vitamin C is also water soluble.

The fat-soluble vitamins A, D, E and K are found in many foods, do not easily get lost in cooking and digest better when accompanied by fat. They are needed in only small amounts, and the excess is stored in the liver and fat tissues, so healthy persons need not consume them in food every day. While no food naturally provides a significant amount of all four vitamins, choosing combinations of healthful foods can help you reach your daily vitamin needs. Fat soluble vitamins in excess can be toxic causing hypervitaminosis.

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