Merck Manual

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Vitamins

Vitamins

Vitamin

Good Sources

Main Functions

Recommended Dietary Allowance for Adults

Safe Upper Limit

Biotin

Liver, kidneys, meats, eggs, milk, fish, dried yeast, sweet potatoes, seeds, and nuts

Required for the processing (metabolism) of carbohydrates and fatty acids

30 micrograms (but no RDA has been established)

35 micrograms for breastfeeding women

Folate (folic acid)

Raw 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, red meat, poultry, fish, legumes, and whole-grain or enriched cereal products and bread

Required for the metabolism of carbohydrates, fats, and many other substances and for the normal functioning of cells

14 milligrams for women

16 milligrams for men

18 milligrams for pregnant women

17 milligrams for breastfeeding women

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)

6 milligrams for pregnant women

7 milligrams for breastfeeding women

Riboflavin (vitamin B2)

Milk, cheese, liver, meat, fish, eggs, and enriched cereals

Required for the metabolism of carbohydrates and proteins 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, proteins, and fats 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, yellow, and orange vegetables and yellow and 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 (pyridoxine)

Dried yeast, liver, other organ meats, whole-grain cereals, fish, and legumes

Required for the metabolism of carbohydrates, amino acids, and fats, for normal nerve function, for the formation of red blood cells, and for healthy skin

1.3 milligrams for younger women and men

1.5 milligrams for women older than 50

1.7 milligrams for men older than 50

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

Formed in the skin when the skin is exposed to direct sunlight

Fortified milk and dairy products, fatty fish, fish liver oils, liver, 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 units for people aged 1‒70

800 units for people older than 70

4,000 units

Vegetable oil, nuts, seeds, green leafy vegetables, and wheat germ

Acts as an antioxidant, protecting cells against damage by free radicals

15 milligrams (22 units of natural or 33 units of synthetic)

19 milligrams for breastfeeding women

1,000 milligrams

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; RNA = ribonucleic acid; RDA=recommended daily allowance.