Many undernourished (see Undernutrition) and critically ill people need additional nutrition (nutritional support). Artificial feeding, which uses commercial nutrient mixtures rather than food, is a common form of nutritional support. Nutritional support is intended to increase the amount of muscle tissue (muscle mass). It usually provides calories as well as vitamins and minerals.
Vitamins are a vital part of a healthy diet. The recommended dietary allowance (RDA)—the amount most healthy people need each day to remain healthy—has been determined for most vitamins. A safe upper limit (tolerable upper intake level) has been determined for some vitamins. Intake above this limit increases the risk of a harmful effect (toxicity).