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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

Water-soluble 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, 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.

Fat-soluble vitamins

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.

Credits

Current as of: September 8, 2021

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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