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.
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 |
Biotin | 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 |
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 |
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 |
Fat-soluble vitamins
Fat-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.
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) |
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. |
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 |
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 |
Related Information
Credits
Current as of: August 22, 2019
Author: Healthwise Staff
Medical Review: Kathleen Romito, MD - Family Medicine
E. Gregory Thompson, MD - Internal Medicine
Rhonda O'Brien, MS, RD, CDE - Certified Diabetes Educator
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Current as of: August 22, 2019
Author: Healthwise Staff
Medical Review: Kathleen Romito, MD - Family Medicine & E. Gregory Thompson, MD - Internal Medicine & Rhonda O'Brien, MS, RD, CDE - Certified Diabetes Educator