Fat-Soluble Vitamins

Vitamins are organic compounds (compounds that contain carbon), and of the 13 that your body needs, 4 are called fat-soluble (A, D, E, and K). Fat-soluble vitamins do not dissolve in water and are stored in your body's fat and liver. As a result, these vitamins can build up in the tissues and become toxic (specifically vitamins A and D).

Vitamins fall into two classes: fat-soluble and water-soluble.

Vitamin A (Retinol)

Like Mom always said, eat plenty of carrots and you'll see in the dark. That's because carrots contain beta-carotene, a substance that is converted into vitamin A by your body. Vitamin A promotes good vision, as well as healthy skin and the normal growth and maintenance of your bones, teeth, and mucous membranes. What Mom didn't tell you was that beta-carotene is also found in most orange-yellow fruits and vegetables, along with dark green vegetables.

Your body converts beta-carotene into vitamin A only when you need it, so eating foods rich in beta-carotene cannot cause vitamin A toxicity. However, eating huge amounts might turn your skin slightly orange. Not to worry, this condition isn't serious. Simply lay off the orange veggies for a few days and the color will disappear.

Although your body controls the creation of vitamin A from beta-carotene, it has no control when you ingest straight vitamin A, which can be found in vitamin tablets. Over-supplementation can be extremely toxic, resulting in general fatigue and weakness, severe headaches, blurred vision, insomnia, hair loss, menstrual irregularities, skin rashes, and joint pain. In extreme cases, there can be liver and brain damage. Huge doses taken in the prenatal period can cause birth defects.

What happens if you don't get enough? Vitamin A deficiency can cause night blindness, total blindness, and lowered resistance to infection because vitamin A plays a key role in the structural integrity of your cells. Here come the germs!

Foods rich in vitamin A include: liver, eggs, milk, butter, and cheese.

Foods rich in beta-carotene include: cantaloupes, carrots, sweet potatoes, winter squash, spinach, and broccoli.

Vitamin D plays an indispensable role in building and maintaining strong bones and teeth. In fact, vitamin D is responsible for the body's absorption and utilization of the mineral calcium. Insufficient amounts of this key vitamin can lead to serious bone abnormalities, including rickets in children (bones that are soft and malformed) and osteoporosis or osteomalacia (softening of the bones) in adults.

Recently, vitamin D has also received a lot of attention for reasons that go far beyond bone health. Research indicates that vitamin D may help prevent autoimmune diseases such as multiple sclerosis, rheumatoid arthritis, psoriasis, and Type 1 diabetes. It may also be a factor in decreasing your risk for cancer of the colon, breast, and prostate.

Because of its potential to help prevent these diseases, several experts think we should be taking in a good deal more vitamin D than the current RDA. In fact, they recommend a whopping 1,000 IU per day! This is well below the tolerable upper limit (UL) of 2,000 IU per day, but some health professionals worry that 1,000 IU may still be too much. Remember—vitamin D is fat-soluble, and therefore can be stored in the body where it may build up to toxic levels. Some of the symptoms of excess vitamin D include drowsiness, diarrhea, loss of appetite, headaches, high blood pressure, high cholesterol, fragile bones, and calcium deposits throughout the body (including heart, kidneys, and blood vessels).

Your best bets for getting enough vitamin D:

• Allow yourself 5–15 minutes of unprotected sun exposure on your hands and arms every day (more if you are darker-skinned). Of course, if you have a history of skin cancer, you must talk to your physician before exposing yourself to UV rays.
• Eat foods rich in vitamin D, such as fortified milk, tuna, salmon, and canned sardines and mackerel.
• Take a daily multivitamin that contains 400–800 IU of vitamin D.

Vitamin E (Tocopherols)

Vitamin E aids the formation and functioning of your red blood cells, muscles, and other tissues, and protects essential fatty acids (special fats that are needed by your body). Because vitamin E is found in a variety of foods, deficiency is rare. However, an extreme case of vitamin E deficiency involves wasting of the muscles and neurological disorders. To date, there have been no shown toxic effects from taking doses well over the RDA.

Foods rich in vitamin E include vegetable oils, salad dressings, whole grain cereals, green leafy vegetables, nuts and seeds, peanut butter, and wheat germ.

Vitamin K

Thanks to vitamin K, you won't bleed to death after an injury. That's because vitamin K is essential for normal blood clotting. Current research also suggests that this vitamin might play a role in maintaining strong bones in the elderly. Where do you get this vitamin? Interestingly enough, bacteria that live in your intestines help to make 80 percent of the vitamin K that you need, and the rest can be found in a variety of foods listed here.

A vitamin K deficiency can cause hemorrhaging (uncontrollable bleeding), mainly in newborn infants because their immature intestinal tracts might not have enough bacteria to make this vitamin. In addition, people taking antibiotics might temporarily lose the ability to make vitamin K because the medication destroys all bacteria, good and bad.

Foods rich in vitamin K include turnip greens, cauliflower, spinach, beef liver, broccoli, kale, and cabbage.

Excerpted from The Complete Idiot's Guide to Total Nutrition © 2005 by Joy Bauer. All rights reserved including the right of reproduction in whole or in part in any form. Used by arrangement with Alpha Books, a member of Penguin Group (USA) Inc.

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