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 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.  | 
              
            
            
              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:  October 7, 2024
               
              
             
           
         
        
        
          
            
              Current as of: October 7, 2024