Vitamins are organic compounds that are needed in small amounts for the body to successfully carry out a number of different functions. Vitamins aid the body in processes essential to life, including growth and reproduction as well as general health. Deficiencies in any of the vitamins can lead to physiological and psychological symptoms. There are two classifications of vitamins: water-soluble and fat-soluble.
Absorption and Storage
Fat-soluble vitamins require the presence of dietary fat in the body in order to be properly absorbed. The fat-soluble vitamins are broken down in fat and carried into the small intestine. The vitamins move through the intestinal wall and combine with fat and other lipids in the body. These lipids carry the fat-soluble vitamins through the lymphatic system and then into the bloodstream.
One of the main differences between fat-soluble vitamins and water-soluble vitamins is that fat-soluble vitamins can be stored by the body. Most of the vitamins are stored in the liver, but some are also stored in the fat and muscle tissues in the body.
Types
There are four fat-soluble vitamins: A, D, E and K. Vitamin A contributes to eye health and immune system function. It is also involved in reproduction and cell division. The richest sources of vitamin A are organ meats, fortified cereals, carrots, spinach and sweet potatoes. Vitamin D contributes to bone and tooth health and regulates calcium levels in the body. Most vitamin D is obtained through sunlight, but vitamin D can also be found in fortified dairy products, fish oils and margarine. Vitamin E is most noted for its antioxidant properties, which help prevent damage to the cells. It also acts like an anticoagulant and prevents the formation of blood clots. Green leafy vegetables, whole grains, nuts, egg yolk and liver are good sources of vitamin E. Vitamin K ensures that blood coagulates properly and aids in proper bone health. Vitamin K is found in green leafy vegetables, vegetable oils and margarine.
Intake Recommendations
The daily recommended intakes differ among each of the fat-soluble vitamins. Each intake recommendation is determined by the Food and Nutrition Board, which is the subdivision of the Institute of Medicine that is responsible for establishing nutrition guidelines. The recommended intake for vitamin A is 700 micrograms, or mcg, per day for adult females and 900 mcg per day for adult males. Intake recommendations for vitamin D vary based on age, but are generally 5 to 15 mcg daily. Regardless of age or gender, adults should aim to consume 15 mg of vitamin E daily. Adult women should consume around 90 mcg of per day and men should consume 120 mcg daily.
Toxicity
Eating a well-balanced diet does not usually contribute to toxicity from fat-soluble vitamins, according to Colorado State University. Risks of toxicity increase in those who consume vitamin supplements that contain large doses of the fat-soluble vitamins. Since fat-soluble vitamins can be stored in the body, supplements are not necessary for well-nourished individuals.
Deficiency
On the other hand, because fat-soluble vitamins can be stored in the body, deficiencies are rare. Deficiencies usually only occur in those who are severely malnourished or those who are going through periods of rapid growth, such as young children or pregnant women.
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