Vitamins are nutrient compounds essential to the functions of the human body. There are thirteen vitamins: A, C, D, E, K and eight classified as B vitamins, including B6, B12, niacin, folate, thiamine, riboflavin, pantothenic acid and biotin, according to MedlinePlus. All are important. Most people get the vitamins they require from food. A well-balanced diet incorporating fruit, vegetables, nuts, meat and dairy products provides every vitamin needed for life.
Vitamin A
Vitamin A is a catch-all term for numerous compounds, including retinol and beta-carotene. These compounds are important for maintaining vision, the body's synthesis of proteins, immune system functions, red blood cell production and growth and development, notes the Linus Pauling Institute of Oregon State University.
Food sources of vitamin A, or of compounds the body converts into vitamin A, include most orange or yellow fruits and vegetables, which get their color from beta-carotene, and most green vegetables. Egg yolks, milk and dairy products also provide vitamin A.
Recommended daily allowances of vitamin A are as follows, in micrograms, or mcg: infants 0 to 6 months need 400 mcg; infants 7 months to 1 year need 500 mcg; toddlers 1 to 3 years need 300 mcg; children 4 to 8 years need 400 mcg; children 9 to 13 years need 600 mcg; adolescent and adult males need 900 mcg and adolescent and adult females need 700 mcg.
Vitamin D
Two compounds, vitamin D2 and vitamin D3, make up the nutrient known as vitamin D. Vitamin D is obtained from food sources and is synthesized in the skin with exposure to UVB radiation from sunlight, explains the Linus Pauling Institute. Most notably, vitamin D is essential to calcium absorption, and it also aids the immune system. It helps regulate cellular functions, insulin levels and blood pressure as well.
Primary food sources of vitamin D include many fish such as salmon, mackerel and sardines, milk, egg yolks and foods fortified with the nutrient.
The recommended daily intake of vitamin D is 5 mcg for everyone up to age 50. To promote calcium absorption and bone health, the recommended daily allowance is higher for older people; adults age 51 to 70 need 10 mcg, and adults 71 and older should get 15 mcg.
Vitamin E
Eight different antioxidant compounds make up the grouping known as vitamin E. This nutrient's primary role is protection against the effects of free radicals. Free radicals cause cell damage that contributes to disease and aging, says Rice University. Vitamin E also helps prevent blood clots and regulate cell functions.
Vitamin E can be obtained from various vegetable oils such as olive, corn and soybean oils; from seeds, nuts and legumes such as sunflower seeds, almonds, hazelnuts and peanuts; and from dark leafy green vegetables.
Recommended daily allowances of Vitamin E are as follows, in milligrams, or mg: infants 0 to 6 months need 4 mg; infants 7 months to 1 year need 5 mg; toddlers 1 to 3 years need 6 mg; children 4 to 8 years need 7 mg; children 9 to 13 years need 11 mg and adolescents and adults need 15 mg.
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