Vitamins: Their Functions and Sources
Vitamins: Their Functions and SourcesSkip to the navigationTopic OverviewThe tables below list the
vitamins, what they do in the body (their functions),
and their sources in food. Water-soluble vitaminsWater-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 |
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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 |
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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 |
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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 |
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Pantothenic acid | Part of an enzyme needed for energy metabolism | Widespread in foods |
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Biotin | Part of an enzyme needed for energy metabolism | Widespread in foods; also produced in intestinal tract by
bacteria |
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Pyridoxine (vitamin B6) | Part of an enzyme needed for protein metabolism; helps make
red blood cells | Meat, fish, poultry, vegetables, fruits |
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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 |
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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 |
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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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Fat-soluble vitaminsFat-soluble vitamins are stored in the body's cells and are not
excreted as easily as water-soluble vitamins. They do not need to be consumed
as often as water-soluble vitamins, although adequate amounts are needed. If
you take too much of a fat-soluble vitamin, it could become toxic. Your body is
especially sensitive to too much vitamin A from animal sources (retinol) and
too much vitamin D. A balanced diet usually provides enough fat-soluble
vitamins. Fat-soluble vitamins| Nutrient | Function | Sources |
|---|
Vitamin A (and its precursor*, beta-carotene) *A precursor is converted by the body to the
vitamin. | Needed for vision, healthy skin and mucous membranes, bone
and tooth growth, immune system health | Vitamin A from animal sources (retinol): fortified milk,
cheese, cream, butter, fortified margarine, eggs, liver Beta-carotene (from plant sources): Leafy, dark green
vegetables; dark orange fruits (apricots, cantaloupe) and vegetables (carrots,
winter squash, sweet potatoes, pumpkin) |
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Vitamin D | Needed for proper absorption of
calcium; stored in bones | Egg yolks, liver, fatty fish, fortified milk, fortified
margarine. When exposed to sunlight, the skin can make vitamin D. |
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Vitamin E | Antioxidant; protects cell walls | Polyunsaturated plant oils (soybean, corn, cottonseed,
safflower); leafy green vegetables; wheat germ; whole-grain products; liver;
egg yolks; nuts and seeds |
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Vitamin K | Needed for proper blood clotting | Leafy green vegetables such as kale, collard greens, and spinach; green vegetables such as broccoli, brussels sprouts, and asparagus; also produced in
intestinal tract by bacteria |
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CreditsByHealthwise Staff
Primary Medical ReviewerKathleen Romito, MD - Family Medicine
E. Gregory Thompson, MD - Internal Medicine
Specialist Medical ReviewerRhonda O'Brien, MS, RD, CDE - Certified Diabetes Educator Current as of:
May 4, 2017 Last modified on: 8 September 2017
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