Vitamins are nutrients required in small amounts to maintain life. Vitamins are called essential because they cannot be made by the human body. They must be obtained from foods or vitamin supplements.
Small amounts of vitamins are essential for life. However, vitamin levels that are too high can cause serious side effects. Dietary Reference Intakes, or DRIs, are used to guide a person's intake of vitamins. DRIs for a particular vitamin are broken down by life-stage and gender groups. These groups reflect a person's age and sex. Four reference values are included in the DRIs.
Estimated Average Requirement, or EAR. This is the daily intake needed to meet the requirements of half the people in a particular group.
Recommended Daily Allowance, or RDA. This is the daily intake that is needed to meet the needs of most individuals in a group.
Adequate Intake, or AI. This value is used when the EAR cannot be determined. It is an estimate of the average daily intake needed for a group.
Tolerable Upper Intake Level, or UL. This is the highest daily intake that a particular group can have without side effects.
Vitamins are divided into two groups: fat soluble and water soluble. The fat-soluble vitamins are A, D, E, and K. These vitamins dissolve in fat. They are transported by fat through the body, and are stored in fat in the body. They are found in fatty foods. Sources include dairy foods, fat, oils, and the fat-containing parts of grains and vegetables.
Water-soluble vitamins dissolve in water-based fluids. These include the eight B vitamins: B1, B2, B3, B6, B12, folate, biotin, and pantothenic acid. Vitamin C also is a water-soluble vitamin.