Vitamins are a vital part of a healthy diet. The recommended dietary allowance (RDA)—the amount most healthy people need each day to remain healthy—has been determined for most vitamins. A safe upper limit (tolerable upper intake level) has been determined for some vitamins. Intake above this limit increases the risk of a harmful effect (toxicity).

Did You Know... Consuming very large doses of vitamins can be harmful.

Consuming too little of a vitamin can cause a nutritional disorder. However, people who eat a variety of foods are unlikely to develop most vitamin deficiencies. Deficiency of vitamin D is an exception. It is common among certain groups of people (such as older people) even if they eat a variety of foods. For other vitamins, a deficiency can develop if people follow a restrictive diet that does not contain enough of a particular vitamin. For example, vegans, who consume no animal products, may become deficient in vitamin B₁₂, which is available in animal products. Deficiency of biotin or pantothenic acid almost never occurs.

Consuming large amounts (megadoses) of certain vitamins (usually as supplements) without medical supervision may also have harmful effects.

Vitamins are called essential micronutrients because the body requires them but only in small amounts.

PrintOpen table in new window
Vitamins Vitamin Good Sources Main Functions Recommended Dietary Allowance Safe Upper Limit Biotin Liver, kidneys, egg yolks, milk, fish, dried yeast, cauliflower, nuts, and legumes Required for the processing (metabolism) of carbohydrates and fatty acids 30 micrograms (but no RDA has been established) — Folate (folic acid) Fresh green leafy vegetables, asparagus, broccoli, fruits (especially citrus), liver, other organ meats, dried yeast, and enriched breads, pastas, and cereals (Note: Extensive cooking destroys 50–95% of the folate in food.) Required for the formation of red blood cells, for DNA and RNA synthesis, and for normal development of the nervous system in a fetus 400 micrograms 600 micrograms for pregnant women 500 micrograms for breastfeeding women 1,000 micrograms Niacin (nicotinic acid or nicotinamide ) Dried yeast, liver, meat, fish, legumes, and whole-grain or enriched cereal products Required for the metabolism of carbohydrates, fats, and many other substances 14 milligrams for women 16 milligrams for men 35 milligrams Pantothenic acid Liver, beef, egg yolks, yeast, potatoes, broccoli, and whole grains Required for the metabolism of carbohydrates and fats 5 milligrams (but no RDA has been established) — Riboflavin (vitamin B2) Milk, cheese, liver, meat, fish, eggs, and enriched cereals Required for the metabolism of carbohydrates and amino acids and for healthy mucous membranes, such as those lining the mouth 1.1 milligrams for women 1.3 milligrams for men 1.4 milligrams for pregnant women 1.6 milligrams for breastfeeding women — Thiamin (vitamin B1) Dried yeast, whole grains, meat (especially pork and liver), enriched cereals, nuts, legumes, and potatoes Required for the metabolism of carbohydrates and for normal nerve and heart function 1.1 milligrams for women 1.2 milligrams for men 1.4 milligrams for pregnant or breastfeeding women — Vitamin A (retinol) As vitamin A: Fish liver oils, liver, egg yolks, butter, cream, and fortified milk As carotenoids (converted to vitamin A in the body), such as beta-carotene: Dark green and yellow-orange vegetables and yellow-orange fruits Required to form light-sensitive nerve cells (photoreceptors) in the retina, helping maintain night vision Helps maintain the health of the skin, cornea, and lining of the lungs, intestine, and urinary tract Helps protect against infections 700 micrograms for women 900 micrograms for men 770 micrograms for pregnant women 1,300 micrograms for breastfeeding women 3,000 micrograms Vitamin B6 Dried yeast, liver, other organ meats, whole-grain cereals, fish, and legumes Required for the metabolism of amino acids and fatty acids, for normal nerve function, for the formation of red blood cells, and for healthy skin 1.3 milligrams 1.5 milligrams for women older than 70 1.7 milligrams for men older than 70 1.9 milligrams for pregnant women 2.0 milligrams for breastfeeding women 100 milligrams Vitamin B12 (cobalamins) Meats (especially beef, pork, liver, and other organ meats), eggs, fortified cereals, milk, clams, oysters, salmon, and tuna Required for the formation and maturation of red blood cells, for nerve function, and for DNA synthesis 2.4 micrograms 2.6 micrograms for pregnant women 2.8 micrograms for breastfeeding women — Vitamin C (ascorbic acid) Citrus fruits, tomatoes, potatoes, broccoli, strawberries, and sweet peppers Required for the formation, growth, and repair of bone, skin, and connective tissue; for healing of wounds and burns; and for normal function of blood vessels Acts as an antioxidant, protecting cells against damage by free radicals Helps the body absorb iron 75 milligrams for women 90 milligrams for men 85 milligrams for pregnant women 120 milligrams for breastfeeding women 35 milligrams more for smokers 2,000 milligrams Vitamin D Formed in the skin when the skin is exposed to direct sunlight Fortified milk, fatty fish, fish liver oils, and egg yolks Promotes the absorption of calcium and phosphorus from the intestine Required for bone formation, growth, and repair Strengthens the immune system and reduces the risk of autoimmune disorders 600 IU for people aged 1‒70 800 IU for people older than 70 4,000 IU Vitamin E Vegetable oil, margarine, nuts, and wheat germ Acts as an antioxidant, protecting cells against damage by free radicals 15 milligrams (22 IU of natural or 33 IU of synthetic) 19 milligrams for breastfeeding women 1,000 milligrams Vitamin K Green leafy vegetables (such as collards, spinach, and kale) and soybean and canola oils Helps in the formation of blood clotting factors and thus is necessary for normal blood clotting Required for healthy bones and other tissues 90 micrograms for women 120 micrograms for men — DNA = deoxyribonucleic acid; IU = international unit; RNA = ribonucleic acid. Vitamins Vitamin Good Sources Main Functions Recommended Dietary Allowance Safe Upper Limit Biotin Liver, kidneys, egg yolks, milk, fish, dried yeast, cauliflower, nuts, and legumes Required for the processing (metabolism) of carbohydrates and fatty acids 30 micrograms (but no RDA has been established) — Folate (folic acid) Fresh green leafy vegetables, asparagus, broccoli, fruits (especially citrus), liver, other organ meats, dried yeast, and enriched breads, pastas, and cereals (Note: Extensive cooking destroys 50–95% of the folate in food.) Required for the formation of red blood cells, for DNA and RNA synthesis, and for normal development of the nervous system in a fetus 400 micrograms 600 micrograms for pregnant women 500 micrograms for breastfeeding women 1,000 micrograms Niacin (nicotinic acid or nicotinamide ) Dried yeast, liver, meat, fish, legumes, and whole-grain or enriched cereal products Required for the metabolism of carbohydrates, fats, and many other substances 14 milligrams for women 16 milligrams for men 35 milligrams Pantothenic acid Liver, beef, egg yolks, yeast, potatoes, broccoli, and whole grains Required for the metabolism of carbohydrates and fats 5 milligrams (but no RDA has been established) — Riboflavin (vitamin B2) Milk, cheese, liver, meat, fish, eggs, and enriched cereals Required for the metabolism of carbohydrates and amino acids and for healthy mucous membranes, such as those lining the mouth 1.1 milligrams for women 1.3 milligrams for men 1.4 milligrams for pregnant women 1.6 milligrams for breastfeeding women — Thiamin (vitamin B1) Dried yeast, whole grains, meat (especially pork and liver), enriched cereals, nuts, legumes, and potatoes Required for the metabolism of carbohydrates and for normal nerve and heart function 1.1 milligrams for women 1.2 milligrams for men 1.4 milligrams for pregnant or breastfeeding women — Vitamin A (retinol) As vitamin A: Fish liver oils, liver, egg yolks, butter, cream, and fortified milk As carotenoids (converted to vitamin A in the body), such as beta-carotene: Dark green and yellow-orange vegetables and yellow-orange fruits Required to form light-sensitive nerve cells (photoreceptors) in the retina, helping maintain night vision Helps maintain the health of the skin, cornea, and lining of the lungs, intestine, and urinary tract Helps protect against infections 700 micrograms for women 900 micrograms for men 770 micrograms for pregnant women 1,300 micrograms for breastfeeding women 3,000 micrograms Vitamin B6 Dried yeast, liver, other organ meats, whole-grain cereals, fish, and legumes Required for the metabolism of amino acids and fatty acids, for normal nerve function, for the formation of red blood cells, and for healthy skin 1.3 milligrams 1.5 milligrams for women older than 70 1.7 milligrams for men older than 70 1.9 milligrams for pregnant women 2.0 milligrams for breastfeeding women 100 milligrams Vitamin B12 (cobalamins) Meats (especially beef, pork, liver, and other organ meats), eggs, fortified cereals, milk, clams, oysters, salmon, and tuna Required for the formation and maturation of red blood cells, for nerve function, and for DNA synthesis 2.4 micrograms 2.6 micrograms for pregnant women 2.8 micrograms for breastfeeding women — Vitamin C (ascorbic acid) Citrus fruits, tomatoes, potatoes, broccoli, strawberries, and sweet peppers Required for the formation, growth, and repair of bone, skin, and connective tissue; for healing of wounds and burns; and for normal function of blood vessels Acts as an antioxidant, protecting cells against damage by free radicals Helps the body absorb iron 75 milligrams for women 90 milligrams for men 85 milligrams for pregnant women 120 milligrams for breastfeeding women 35 milligrams more for smokers 2,000 milligrams Vitamin D Formed in the skin when the skin is exposed to direct sunlight Fortified milk, fatty fish, fish liver oils, and egg yolks Promotes the absorption of calcium and phosphorus from the intestine Required for bone formation, growth, and repair Strengthens the immune system and reduces the risk of autoimmune disorders 600 IU for people aged 1‒70 800 IU for people older than 70 4,000 IU Vitamin E Vegetable oil, margarine, nuts, and wheat germ Acts as an antioxidant, protecting cells against damage by free radicals 15 milligrams (22 IU of natural or 33 IU of synthetic) 19 milligrams for breastfeeding women 1,000 milligrams Vitamin K Green leafy vegetables (such as collards, spinach, and kale) and soybean and canola oils Helps in the formation of blood clotting factors and thus is necessary for normal blood clotting Required for healthy bones and other tissues 90 micrograms for women 120 micrograms for men — DNA = deoxyribonucleic acid; IU = international unit; RNA = ribonucleic acid.

Some vitamins—A, D, E, and K—are fat soluble. Other vitamins—B vitamins and vitamin C—are water soluble. B vitamins include biotin, folate (folic acid), niacin, pantothenic acid, riboflavin (vitamin B₂), thiamin (vitamin B₁), and vitamins B₆ (pyridoxine) and B₁₂ (cobalamins).

Vitamins: Fat Versus Water Soluble
Vitamins are classified as fat soluble: Vitamin A Vitamin D Vitamin E Vitamin K or water soluble: B vitamins Vitamin C This difference affects nutrition in several ways. Fat-soluble vitamins: These vitamins dissolve in fats (lipids). They are stored in the liver and in fatty tissues. If too much of the fat-soluble vitamins A or D are consumed, they can accumulate and may have harmful effects. Because fats in foods help the body absorb fat-soluble vitamins, a low-fat diet may result in a deficiency. Some disorders interfere with absorption of fats and thus of fat-soluble vitamins. Examples are chronic diarrhea, Crohn disease, cystic fibrosis, certain pancreatic disorders, and blockage of the bile ducts. Some drugs, such as mineral oil, have the same effect. Fat-soluble vitamins dissolve in mineral oil, which the body does not absorb. So when people take mineral oil, it carries these vitamins unabsorbed out of the body. Cooking does not destroy fat-soluble vitamins. Water-soluble vitamins: These vitamins dissolve in water. They are eliminated in urine and tend to be eliminated from the body more quickly than fat-soluble vitamins. Water-soluble vitamins are more likely to be destroyed when food is stored and prepared. Refrigerating fresh produce, storing milk and grains out of strong light, and using the cooking water from vegetables to prepare soups can help prevent the loss of the vitamins.

The body does not store most vitamins. Therefore, people must consume them regularly. Vitamins A, B₁₂, and D are stored in significant amounts, mainly in the liver.

Disorders that impair the intestine's absorption of food (called malabsorption disorders) can cause vitamin deficiencies. Some disorders impair the absorption of fats. These disorders can reduce the absorption of fat-soluble vitamins—A, D, E, and K—and increase the risk of a deficiency. Such disorders include chronic diarrhea, Crohn disease, cystic fibrosis, certain pancreatic disorders, and blockage of the bile ducts.

Some types of weight-loss (bariatric) surgery can also interfere with absorption of vitamins.

Liver disorders and alcoholism can interfere with the processing (metabolism) or storage of vitamins. In a few people, hereditary disorders impair the way the body handles vitamins and thus cause a deficiency.

Drugs can also contribute to deficiency of a vitamin. They may interfere with absorption, metabolism, or storage of a vitamin.

Because many people eat irregularly or do not eat a variety of foods, they may not get enough of some vitamins from foods alone. If they do not get enough, the risk of certain cancers or other disorders may be increased. People may then take a multivitamin. However, for most people, taking multivitamins does not appear to reduce risk of developing cancer.

PrintOpen table
Some Drugs That Cause Vitamin Deficiency Drug Vitamin Alcohol Folate Thiamin Vitamin B6 Antacids Vitamin B12 Antibiotics, such as isoniazid, tetracycline, and trimethoprim-sulfamethoxazole B vitamins Folate Vitamin K Anticoagulants, such as warfarin Vitamin E Vitamin K Anticonvulsants, such as phenytoin and phenobarbital Biotin Folate Vitamin B6 Vitamin D Vitamin K Antipsychotic drugs Riboflavin Vitamin D Barbiturates such as phenobarbital Folate Riboflavin Vitamin D Chemotherapy drugs, such as methotrexate Folate Cholestyramine Vitamin A Vitamin D Vitamin E Vitamin K Corticosteroids Vitamin C Vitamin D Cycloserine Vitamin B6 Hydralazine Vitamin B6 Levodopa Vitamin B6 Mineral oil (long-term use) Vitamin A Vitamin D Vitamin E Vitamin K Metformin Folate Vitamin B12 Nitrous oxide (repeated exposure) Vitamin B12 Oral contraceptives Folate Thiamin Vitamin B6 Penicillamine Vitamin B6 Phenothiazines Riboflavin Primidone Folate Vitamin D Rifampin Vitamin D Vitamin K Sulfasalazine Folate Thiazide diuretics Riboflavin Triamterene Folate Tricyclic antidepressants, such as amitriptyline and imipramine Riboflavin Some Drugs That Cause Vitamin Deficiency Drug Vitamin Alcohol Folate Thiamin Vitamin B6 Antacids Vitamin B12 Antibiotics, such as isoniazid, tetracycline, and trimethoprim-sulfamethoxazole B vitamins Folate Vitamin K Anticoagulants, such as warfarin Vitamin E Vitamin K Anticonvulsants, such as phenytoin and phenobarbital Biotin Folate Vitamin B6 Vitamin D Vitamin K Antipsychotic drugs Riboflavin Vitamin D Barbiturates such as phenobarbital Folate Riboflavin Vitamin D Chemotherapy drugs, such as methotrexate Folate Cholestyramine Vitamin A Vitamin D Vitamin E Vitamin K Corticosteroids Vitamin C Vitamin D Cycloserine Vitamin B6 Hydralazine Vitamin B6 Levodopa Vitamin B6 Mineral oil (long-term use) Vitamin A Vitamin D Vitamin E Vitamin K Metformin Folate Vitamin B12 Nitrous oxide (repeated exposure) Vitamin B12 Oral contraceptives Folate Thiamin Vitamin B6 Penicillamine Vitamin B6 Phenothiazines Riboflavin Primidone Folate Vitamin D Rifampin Vitamin D Vitamin K Sulfasalazine Folate Thiazide diuretics Riboflavin Triamterene Folate Tricyclic antidepressants, such as amitriptyline and imipramine Riboflavin

Last full review/revision February 2013 by Larry E. Johnson, MD, PhD