Everyone needs vitamins, substances that the body usually can't manufacture in the full amounts needed and must be obtained from your diet. Vitamins come in two types: water-soluble and fat-soluble. As the names suggest, fat-soluble vitamins dissolve in lipids, or fats, and water-soluble vitamins dissolve in liquids. Vitamins A, D, E and K make up the fat-soluble vitamins. Your body can make some of the vitamin D and K you need; vitamin D is manufactured in the skin when exposed to adequate amounts of sunlight, and vitamin K is synthesized in the intestine.
Supply
Your body utilizes every type of vitamin everyday to perform a number of essential functions. However, while you must get the required water-soluble vitamins each day through your diet, you don't need to consume all the fat-soluble vitamins you need during a single day. Fat-soluble vitamins can be stored in the liver and in fat cells, which can release them as needed. If you build up adequate stores of vitamin D in the summer months, the stores will last 30 to 60 days, according to DermNet NZ.
Fat Requirements
Fat-soluble vitamins must dissolve in fat before they can enter the bloodstream. Malabsorption diseases such as inflammatory bowel disease or cystic fibrosis, which decrease the amount of fat your body can absorb from the intestine, can also decrease the absorption of fat-soluble vitamins. Vitamin A deficiency can cause night blindness and other visual problems, while vitamin D deficiency can cause soft bones. Vitamin E deficiency rarely occurs unless a person is starving. Vitamin K deficiency can cause excessive bleeding.
Potential for Toxicity
Because fat-soluble vitamins can be stored in fat cells, it's much easier to overdose on fat-soluble vitamins than on water-soluble vitamins. Do not take additional supplements of fat-soluble vitamins beyond the amount contained in a standard multivitamin without talking to your doctor first. Excess amounts of water-soluble vitamins are normally excreted in the urine, but excess fat-soluble vitamins build up over time and can cause serious toxic reactions. Fat-soluble vitamin toxicity rarely occurs from eating foods that contain fat-soluble vitamins, but rather occur if you take too many vitamin supplements. Vitamin A overdose can cause birth defects, liver problems and skin disorders as well as growth retardation. Vitamin D toxicity can cause kidney damage and calcium deposits that can damage the heart. Excess vitamin E can cause increased bleeding, nausea and other digestive disorders, while vitamin K overdose has no known side effects.
Vitamin Loss
Water-soluble vitamins such as the B-complex vitamins and vitamin C can be easily destroyed by heating and cooking in water. Heating does not destroy fat-soluble vitamins to the same degree.
References
- Colorado State University Extension: Fat-Soluble Vitamins; J. Anderson, et al.; August 2008
- Ohio State University: Fat-Soluble Vitamins
- DermNet NZ: Vitamin D
- National Health Service, UK: Vitamins and Minerals
- Merck Manuals Online Medical Library: Malabsorption Syndromes; Atenodoro R. Ruiz, Jr., M.D.; January 2008
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