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Vitamins: Their Functions and Sources - Topic Overview

The tables below list the vitamins, what they do in the body (their functions), and their sources in food.

Water-soluble vitamins

Water-soluble vitamins travel freely through the body, and excess amounts usually are excreted by the kidneys. The body needs water-soluble vitamins in frequent, small doses. These vitamins are not as likely as fat-soluble vitamins to reach toxic levels. But niacin, vitamin B6, folate, choline, and vitamin C have upper consumption limits. Vitamin B6 at high levels over a long period of time has been shown to cause irreversible nerve damage.

A balanced diet usually provides enough of these vitamins. People older than 50 and some vegetarians may need to use supplements to get enough B12.

Water-soluble vitamins
Nutrient Function Sources

Thiamine (vitamin B1)

Part of an enzyme needed for energy metabolism; important to nerve function

Found in all nutritious foods in moderate amounts: pork, whole-grain or enriched breads and cereals, legumes, nuts and seeds

Riboflavin (vitamin B2)

Part of an enzyme needed for energy metabolism; important for normal vision and skin health

Milk and milk products; leafy green vegetables; whole-grain, enriched breads and cereals

Niacin (vitamin B3)

Part of an enzyme needed for energy metabolism; important for nervous system, digestive system, and skin health

Meat, poultry, fish, whole-grain or enriched breads and cereals, vegetables (especially mushrooms, asparagus, and leafy green vegetables), peanut butter

Pantothenic acid

Part of an enzyme needed for energy metabolism

Widespread in foods


Part of an enzyme needed for energy metabolism

Widespread in foods; also produced in intestinal tract by bacteria

Pyridoxine (vitamin B6)

Part of an enzyme needed for protein metabolism; helps make red blood cells

Meat, fish, poultry, vegetables, fruits

Folic acid

Part of an enzyme needed for making DNA and new cells, especially red blood cells

Leafy green vegetables and legumes, seeds, orange juice, and liver; now added to most refined grains

Cobalamin (vitamin B12)

Part of an enzyme needed for making new cells; important to nerve function

Meat, poultry, fish, seafood, eggs, milk and milk products; not found in plant foods

Ascorbic acid (vitamin C)

Antioxidant; part of an enzyme needed for protein metabolism; important for immune system health; aids in iron absorption

Found only in fruits and vegetables, especially citrus fruits, vegetables in the cabbage family, cantaloupe, strawberries, peppers, tomatoes, potatoes, lettuce, papayas, mangoes, kiwifruit

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