Fat-soluble vitamins are essential to the growth and maintenance of many body systems. They influence eyes, skin, digestion, cell breakdown and protein storage. Many foods contain fat-soluble vitamins, but some instances exist in which no food sources are required to obtain these essential micronutrients.
Identification
The fat-soluble vitamins are vitamins A, D, E and K. They are different from water-soluble vitamins in that they are not absorbed directly into the blood, may require protein carriers, and are stored in cells associated with fat. Fat-soluble vitamins are less readily excreted and thus are more likely than water-soluble vitamins to reach toxic levels when taken as a supplement. For this reason, it is best to get the essential fat-soluble vitamins from food and environmental sources.
Vitamin A
Vitamin A is used in the body to promote healthy vision, skin and aid in protein synthesis, reproduction and growth. Vitamin A comes in three forms: retinol, retinal and retinoic acid. They are found in animal-derived foods, such as fortified milk, cheese, cream, butter, margarine, eggs and liver. Some plant foods contain carotenoids, such as beta-carotene, which are converted to vitamin A in the body. Plant foods containing carotenoids include spinach, dark leafy greens, broccoli, deep orange fruits and vegetables such as apricots, cantaloupe, squash, carrots, sweet potatoes and pumpkin.
Vitamin D
Vitamin D is different than any other fat-soluble vitamin in that the body can synthesize it from sunlight. To obtain adequate vitamin D, dark-skinned people require about three hours of sunlight daily on their forearms and face, and fair-skinned people require about 30 minutes of sunlight. Vitamin D can also be found in fortified milk, margarine, cereal, oil, veal, beef and egg yolks. The main function of vitamin D in the body is the mineralization of bones.
Vitamin E
Vitamin E is an antioxidant, meaning it stabilizes the lipid component of cell membranes, preventing them from destruction. Vitamin E also regulates oxidation reactions in the body and prevents destruction of vitamin A. Significant sources of vitamin E include polyunsaturated plant oils, such as canola oil and olive oil found in margarine, salad dressings and shortenings. Vitamin E is also found in leafy green vegetables, wheat germ, whole grains, liver, egg yolks, nuts and seeds.
Vitamin K
Vitamin K can be obtained without food consumption. The gastrointestinal tract, or large intestine, uses bacteria to make vitamin K, which has the primary use of blood clotting, but also is used in the activation of several bone proteins. Food sources of vitamin K include liver, leafy green vegetables, cabbage-type vegetables and milk.
References
- "Understanding Nutrition"; Ellie Whitney and Sharon Rady Rolfes; 2005
- U.S. Department of Agriculture: My Pyramid
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