Recommended Dietary Allowances For Vitamins

There are 13 vitamins essential in very small amounts for human health. They are divided into two classes: water soluble and fat soluble. Some vitamins are measured in international units (IUs), a measure of biological activity, whereas others are measured by weight, in micrograms (mcg) or milligrams (mg). For each vitamin, there is a recommended dietary intake (RDA) or adequate intake level (AI) to avoid deficiency symptoms and diseases.

Fat-Soluble Vitamins

There are four fat-soluble vitamins: A, D, E, and K, which are typically found in fatty foods. There is an RDA for vitamins A and E, and an AI value for D and K. Vitamin A is unique because it is not measured by weight or biological activity (IU). Because it has several forms, vitamin A is measured in retinol activity equivalents (RAE). One RAE equals 1 mcg of retinol, 12 mcg of beta-carotene or 24 mcg of other vitamin A precursor carotenoids. The RDA for vitamin A for men is 900 mcg RAE, and for women it is 700 mcg RAE. The RDA for vitamin E is 15 mg for men and women.
Our bodies manufacture both vitamin K (in our large intestine) and vitamin D (from sunlight exposure), but there is an AI level for both vitamins. The AI for cholecalciferol (the active form of vitamin D) for adults aged 31 to 50 years is 5 mcg. For those younger than 51, the AI is 10 mcg. The AI for vitamin K is 120 mcg for men and 90 mcg for women.

Water-Soluble Vitamins

Water-soluble vitamins include the B-complex vitamins and vitamin C. The RDA for vitamin C is 90 mg for men and 75 mg for women. The RDA for thiamin and riboflavin (vitamins B1 and B2, respectively) is the same: 1.2 mg for men and 1.1 mg for women. For niacin (vitamin B3), the RDA for men is 16 mg of niacin equivalents and for women 14 mg (niacin equivalents include both synthetic forms from supplements and fortified foods). The RDA for vitamins B6 and B12 for men and women are 1.3 mg and 2.4 mg, respectively. The RDA for folate (folic acid in synthetic forms) is 400 mcg dietary folate equivalents (DFEs). DFEs include both synthetic forms from supplements and fortified foods. Two other B-vitamins include pantothenic acid and biotin. The AI for pantothenic acid and biotin is 5 mg for men and 30 mcg for women .

Choline and Vitaminlike Substances

Choline is a conditionally essential nutrient. The body makes some choline, but not enough to meet all of our needs, and a lack of choline in the diet may result in liver damage. This is rare because choline is found in many foods. There is an AI value for this nutrient. Men require 550 mg and women need 425 mg daily. There are many vitamin-like substances, such as carnitine, lipoic acid, inositol and taurine. Although necessary for metabolism, these nutrients are not essential because our bodies make enough to meet our needs.