Fat-soluble vitamins combine with fatty acids and bile in your digestive tract so that your body can absorb them. These four vitamins are absorbed at the beginning of your small intestine, where they combine with fat and chylomicrons -- a type of lipoprotein -- and travel to your lymphatic system where they circulate before entering your blood. Each fat-soluble vitamin performs a different function.
Vitamin K
Vitamin K plays an essential role in blood clotting. The vitamin ensures that your blood is able to form clots to prevent excess bleeding when your blood vessels become damaged. Vitamin K also regulates the action of a protein called osteocalcin, which is vital to keeping your bones healthy.
Vitamin K exists in two forms: menaquinone and phylloquinone. The bacteria that live in your intestinal tract synthesize the menaquinone form of vitamin K. You must obtain phylloquinone vitamin K from the foods you eat. The best sources of vitamin K in the diet are green vegetables, such as broccoli, Brussels sprouts, spinach, asparagus, cabbage and salad greens. You can also obtain vitamin K from vegetable oils and some margarines.
Vitamin D
Vitamin D stimulates the absorption of calcium and phosphorus in your intestinal tract, ensuring that your blood contains enough of the minerals to form healthy bones. Vitamin D also regulates the growth and differentiation of many cells in your body.
Your skin can synthesize vitamin D with the aid of ultraviolet sun rays. Because it is not clear how much vitamin D your skin can make, however, you should also consume vitamin D from your diet. Few foods provide vitamin D. They include fortified milk, salmon, sardines, yogurt and fortified cereals.
Vitamin A
The light-sensitive proteins in your eyes rely on vitamin A to convert light into images. Vitamin A also ensures that your eyes are able to adapt to darkness. Vitamin A also plays a role in the health of your immune system, keeps your skin healthy and allows a fetus to develop correctly.
Vitamin A is available in a wide variety of foods including meat, milk, cheese, eggs, fish, carrots, spinach, sweet potatoes, winter squash, pink grapefruit and green leafy vegetables. "Nutrition and You" by Joan Salge Blake notes that adding 1 tbsp. of fat, such as olive oil, to your diet can increase the absorption of vitamin A in your intestinal tract.
Vitamin E
Free radicals are harmful substances that damage your cell membranes and increase your risk of developing chronic diseases. Vitamin E acts as an antioxidant, which neutralizes free radicals before they are able to cause any damage to your cells. Vitamin E also functions as an anticoagulant, preventing blood from clotting abnormally.
The richest sources of vitamin E include vegetable oils and foods that are naturally high in oil, such as nuts and seeds. Green leafy vegetables -- such as spinach, kale and salad greens -- are also good sources of vitamin E.
References
- "Nutrition and You"; Joan Salge Blake; 2008
- MedlinePlus: Vitamin A
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