The body cannot make vitamins, but it needs them to function; they must be taken in from foods.
An adequate supply of vitamins from the diet or through nutritional supplements is required for growth, health, and life.
Although essential, only tiny amounts of vitamins are needed each day for normal function.
Vitamins are not a source of calories, but several vitamins do help convert food into energy.
Inadequate intake of a vitamin will lead to symptoms of deficiency.
There are 13 vitamins divided into two classes: fat-soluble and water-soluble.
What are the fat-soluble vitamins?
The fat-soluble vitamins are vitamins A, D, E, and K.
Fat-soluble vitamins are primarily found in fatty foods, such as milk, milk products, eggs, vegetable oils, nuts, and seeds.
A small amount of fat must be present in the body for it to absorb the fat-soluble vitamins.
These vitamins are stored in the fatty areas of the body, and, in the cases of vitamin A and vitamin D, can build up to toxic levels if intake is too high.
Some of the important functions of various fat-soluble vitamins include maintaining healthy vision (vitamin A), protecting the body from free radical damage (vitamin E), helping the blood clot (vitamin K), and ensuring that calcium is absorbed and used (vitamin D).
What are the water-soluble vitamins?
The water-soluble vitamins are vitamin C and the B vitamins (B1, B2, niacin [B3], pantothenic acid [B5], B6, folic acid, B12, and biotin).
Water-soluble vitamins are found in the watery parts of food; rich sources of these vitamins are fruits and vegetables.
Most of the water-soluble vitamins, with the exception of niacin, are harmless at high intakes, since excesses are excreted in the urine.
The water-soluble vitamins perform many functions in the body, such as acting as antioxidants, converting food into energy, reducing the risk of birth defects, and maintaining healthy brain function.
How do the B vitamins affect health?
The B vitamins are not all related to one another chemically; they are grouped together because they are found in the same foods.
The B vitamins perform many similar and supportive functions in the body.
There are eight B vitamins: thiamine (vitamin B1), riboflavin (vitamin B2), niacin (vitamin B3), pantothenic acid (vitamin B5), pyridoxine (vitamin B6), folic acid, cobalamin (vitamin B12), and biotin.
B vitamins are needed to convert food into energy and to maintain a healthy nervous system.
Deficiencies of the B vitamins tend to occur together, since they are found in the same foods, such as whole grain breads and cereals and dark green leafy vegetables.
Why is folic acid important for women?
Adequate folic acid intake is particularly important in the weeks just before and just after conception to prevent birth defects, such as spina bifida.
All women of childbearing age should consume 400 mcg of folic acid daily from dietary and/or supplement sources.
A deficiency of folic acid increases a woman's risk for developing cervical cancer; folic acid supplements might protect women from this cancer.
What are the important roles of other B vitamins?
The B vitamins are not a source of calories, but they do provide energy through their essential role in the processing of carbohydrates, fats, and protein into energy.
Too little vitamin B12 or folic acid leads to anemia, which can cause fatigue, poor concentration, and irritability.
Supplements of vitamin B6 might alleviate the pain and stiffness of carpal tunnel syndrome.
Symptoms of premenstrual syndrome are relieved in some women taking vitamin B6 supplements.
Niacin supplements, in the form of nicotinic acid, reduce cholesterol levels. Another form of niacin, called inositol hexaniacinate, may also lower cholesterol levels.
What is vitamin E?
Vitamin E is actually a family of fat-soluble compounds that include four tocopherols and four tocotrienols. Alpha tocopherol is the most common and potent form of vitamin E.
The Recommended Dietary Allowance (RDA) of vitamin E is 15 IU each day.
A higher intake of this vitamin is needed when the diet contains greater amounts of polyunsaturated fats.
Much larger amounts of vitamin E than the RDA, such as 100–200 IU of vitamin E per day, are safe and might provide additional health benefits.
Vegetable oils and seeds contain the greatest concentrations of vitamin E.
How does vitamin E protect health?
Vitamin E is a powerful antioxidant that protects the fatty areas of the body, such as cell membranes, from free radical attack.
Vitamin E protects the lungs from free radicals found in air pollution.
Other antioxidants, including vitamin C and selenium, enhance the antioxidant abilities of vitamin E.
Free radicals contribute to some of the signs of premature aging, such as skin changes and memory loss, and vitamin E might guard against this type of free radical damage.
What are other health benefits of vitamin E?
Vitamin E is needed to make red blood cells and keep them healthy.
Supplements of vitamin E daily reduce the risk of heart disease.
Plenty of vitamin E in the diet or from supplements lessens the risk of cancer, aids athletic performance, and alleviates some of the symptoms of premenstrual syndrome.
What is vitamin C?
Vitamin C, a water-soluble vitamin, is needed to prevent scurvy, the vitamin C-deficiency disease.
Recommended Dietary Allowance (RDA) of vitamin C for nonsmoking adults is 75 mg per day for womenand 90 mg per day for men. However, doctors often recommend 500–1,000 mg per day or more.
Cigarette smokers require higher intakes of vitamin C; the RDA for smokers is currently 110 mg and 125 mg per day, respectively.
Vitamin C is generally safe even at very high intakes. However, megadoses (more than 4 grams per day) may cause diarrhea in some individuals.
Higher intakes of vitamin C, such as 250–2,000 mg per day, might provide additional health benefits.
What does vitamin C do?
Vitamin C helps in the healing of wounds, bone fractures, bruises, and bleeding gums.
As an antioxidant, vitamin C protects against free radical damage in the watery areas of the body, such as the blood and fluid within and around each cell.
Optimal intake of vitamin C increases resistance to infections. Supplements of vitamin C reduce the duration and severity of the common cold.
Vitamin C is needed to make collagen, a protein found in skin, tendons, bones, teeth, and many other parts of the body.
What are other health benefits of vitamin C?
Extra vitamin C might be needed during times of stress, since stress depletes the body's stores of vitamin C.
Heart disease is less likely in people with higher dietary intakes of vitamin C.
The antioxidant properties of vitamin C reduce the risk of developing cancer.
Vitamin C is needed for healthy vision and might help prevent cataracts and macular degeneration.