While water-soluble vitamins dissolve in water and can be digested without the presence of lipids, or fats, in the digestive tract, the body requires the presence of lipids to metabolize fat-soluble vitamins, according to the National Cancer Institute. The body also excretes excess water-soluble vitamins while it stores excess fat-soluble vitamins in the liver and fatty tissues. Because fat-soluble vitamins, which include vitamins A, D, E and K, can be stored, daily intake isn't required, but a healthy balanced diet rich in fat-soluble vitamins is still essential to health.
Vitamin A
Vitamin A is essential for vision, bone growth, fertility, cell division and differentiation, immune function and mucus membrane health, according to the National Institutes of Health Office of Dietary Supplements. There are two basic categories of vitamin A: preformed vitamin A, which is found in animal foods, and provitamin A carotenoid, which is found in plant foods. Preformed vitamin A has higher bioavailability, which means that it's easier for the body to metabolize and utilize preformed vitamin A than provitamin A carotenoid. The recommended dietary allowance, or RDA, of vitamin A is 700 IU for adult women and 900 IU for adult men. Rich animal sources of vitamin A include beef and chicken liver, fortified milk, cheese and eggs. Carrots, green leafy vegetables, cantaloup, apricots, mango, papaya, peaches, peas and sweet red peppers are all excellent plant-based vitamin A sources.
Vitamin D
Vitamin D aids calcium absorption, bone growth and remodeling and healthy neuromuscular and immune function. When human skin is exposed to ultraviolet B radiation from the sun it converts cutaneous 7-dehydrocholesterol into vitamin D, but food sources of vitamin D are relatively limited. The RDA of vitamin D is 200 IU from birth to age 50, 400 IU from age 51 to 70 and 600 IU after age 71. Vitamin D from food sources comes in two varieties: vitamin D3, which is found in animal products, and vitamin D2 which is found in mushrooms. Mushrooms artificially exposed to ultraviolet light have even higher levels of vitamin D2. Foods that don't normally contain high levels of vitamin D are also fortified with vitamin D3 to supplement dietary intake. Animal sources of vitamin D include cod liver oil, salmon, mackerel, tuna, fortified milk and juices, sardines, beef liver, fortified cereals and eggs.
Vitamin E
Vitamin E actually refers to eight different chemical compounds with antioxidant properties, but only one of the eight is considered to be bioavailable to humans. Theoretically, antioxidants help the body fight free radicals, or molecules with an unshared electron that can damage cells and may play a role in the development of heart disease and cancer. Adults should consume 22.4 IU of vitamin E per day. Wheat germ, nuts, seeds, green leafy vegetables, kiwi, mango and tomatoes are among the best sources of vitamin E.
Vitamin K
Vitamin K promotes normal blood clotting and healthy bone growth, according to Colorado State University. The RDA of vitamin K is 120 mcg per day for adult males and 90 mcg per day for adult females. Vitamin K is produced by intestinal bacteria, but can also be found in green leafy vegetables, soybean oil, cottonseed oil, olive oil and canola oil.
References
- Colorado State University: Fat Soluble Vitamins
- National Cancer Institute: Fat-Soluble Vitamin
- National Institutes of Health Office of Dietary Supplements: Dietary Supplement Fact Sheet: Vitamin A and Carotenoids
- National Institutes of Health Office of Dietary Supplements: Dietary Supplement Fact Sheet: Vitamin D
- National Institutes of Health Office of Dietary Supplements: Vitamin E
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