Vitamins: Their Functions and Sources
Overview
Vitamins are divided into two categories.
- Water-soluble vitamins
- These travel freely through the body. The part that the body doesn't use passes through the kidneys and leaves the body as urine or stool. The body needs water-soluble vitamins in frequent, small doses. They aren't likely to reach toxic levels.
- Fat-soluble vitamins
- These are stored in the body's cells. They are not passed out of the body as easily as water-soluble vitamins. Fat-soluble vitamins can reach toxic levels if you get more than you need.
A balanced diet usually provides enough water-soluble and fat-soluble vitamins. People older than 50 and some vegetarians may need to use supplements to get enough B12.
Vitamins
Vitamin | What it does | Where it's found |
|---|---|---|
Thiamine (vitamin B1) | Part of an enzyme needed for energy metabolism; important for 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 or 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. |
Folate (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 for 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. |
Vitamin | What it does | Where it's found |
|---|---|---|
Vitamin A (and its precursor*, beta-carotene) [*A precursor is converted to the vitamin by the body.] | Needed for vision, healthy skin and mucous membranes, bone and tooth growth, immune system health. | Vitamin A from animal sources: 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 (kale, collard greens, and spinach); green vegetables (broccoli, brussels sprouts, and asparagus); also produced in the intestinal tract by bacteria. |
Current as of: October 7, 2024
Author: Ignite Healthwise, LLC Staff
Clinical Review Board
All Healthwise education is reviewed by a team that includes physicians, nurses, advanced practitioners, registered dieticians, and other healthcare professionals.