Vitamins: Their Functions and Sources
Vitamins: Their Functions and Sources
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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 foods 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 foods, 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 foods, 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 |
| 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.
A balanced diet usually provides enough fat-soluble vitamins. You may find it more difficult to get enough vitamin D from food alone and may consider taking a vitamin D supplement or a multivitamin with vitamin D in it. Refer to HealthLinkBC File #68e Food Sources of Calcium and Vitamin D for food source ideas and information on supplements. Talk to your health care provider about the right supplement for you.
| 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 |
Adaptation Date: 1/23/2023
Adapted By: HealthLink BC
Adaptation Reviewed By: HealthLink BC
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