Recommended dietary allowances, or RDA, of vitamins are set at levels that are supposed to prevent obvious deficiency symptoms in 97 to 98 percent of people. Meeting these levels each day is important to prevent deficiency, although many health professionals believe that "mega-dosing" some vitamins is essential to promote health. The RDA of vitamins varies dramatically, and is measured in micrograms, milligrams or International Units.
Vitamin A
Vitamin A, or retinol, is an antioxidant that is essential for promoting healthy vision and forming mucous membranes. According to the National Institutes of Health, the RDA is 300 mcg per day for infants, 900 mcg daily for men and up to 1,300 mcg for lactating women. Very large doses are toxic.
Vitamins B-1, B-2 and B-3
Vitamin B-1, or thiamine, is required for the metabolism of simple sugars and amino acids. The RDA ranges from 0.2 mcg for infants less than six months, to 2.8 mcg for lactating women. Vitamin B-2, or riboflavin, is required for the metabolism of fats, ketone bodies, carbohydrates and proteins. The RDA ranges from 0.3 mg for infants less than six months, to 1.6 mg for lactating women. Vitamin B-3, or niacin, is required for DNA repair and the production of sex hormones. The RDA ranges from 2 mg in infants less than six months, to 17 mg for lactating women. Large doses of niacin cause flushing and tingling around the face and neck of some people.
Vitamins B-5, B-6 and B-7
Vitamin B-5, or pantothenic acid, is required to synthesize coenzyme-A and metabolize food into energy. The RDA ranges from 1.7 mg in infants less than six months, to 7 mg for lactating women. Pantothenic acid is considered the best "stress vitamin," according to "The Vitamins." Vitamin B-6, or pyridoxine, is required for amino acid metabolism and to govern the release of glucose from glycogen, making it a primary "energy vitamin." The RDA ranges from 0.1 mg in infants less than six months, to 2 mg for lactating women. Very large doses are toxic to nerves. Vitamin B-7, or biotin, is required for cell growth, fatty acid production and amino acid metabolism. The RDA ranges from 5 mcg in infants less than six months, to 35 mcg for lactating women.
Vitamins B-9 and B-12
Vitamin B-9, or folic acid, is required to synthesize and repair DNA and contributes to red blood cell prosuction. The RDA ranges from 150 mcg in infants less than 6 months, to 600 mcg for pregnant women. Deficiency during pregnancy increases the risk of neural tube defects in newborns, according to "Human Biochemistry and Disease." Vitamin B-12, or cobalamin, is required to synthesize DNA and to help maintain healthy neurons and red blood cells. The RDA ranges from 0.4 mcg in infants less than 6 months, to 2.8 mcg for lactating women.
Vitamin C
Vitamin C, or ascorbic acid, is a powerful antioxidant that enhances immunity, protects blood vessels and maintains elasticity of skin and connective tissue. The RDA is between 75 and 120 mg per day for adults, depending on whether they smoke.
Vitamin D
Vitamin D is synthesized within the skin from sun exposure and is important for immune function and strong bones. As a supplement, the RDA is 400 IU daily for infants, whereas most adults require 600 IU, and those older than 70 need 800 IU.
Vitamin E
Vitamin E is also a powerful antioxidant that protects tissues from damage and it helps regulate sex hormones. The RDA ranges from about 22 to 28 IU per day for adults.
Vitamin K
Vitamin K is required for coagulation and normal blood clotting. The RDA for adults ranges from 90 to 120 mcg daily, depending on age and pregnancy.
References
- National Health Institutes: Office of Dietary Supplements: Vitamin A Fact Sheet
- "The Vitamins, Third Edition"; Gerald F. Combs; 2007
- "Human Biochemistry and Disease"; Gerald Litwack; 2008
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