Healthy Eating: Valuable Vitamins
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Out of the thirteen vitamins your body needs, four of them are fat-soluble vitamins. These four vitamins are vitamin A, D, E, and K. Fat-soluble vitamins dissolve in fat and are carried throughout your body attached to body chemicals made with fat. This is one important reason you need moderate amounts of fat in your daily diet. The body can store fat-soluble vitamins in its fat stores and in the liver. For this reason, consuming too much of a fat-soluble vitamin, usually in a supplemental form, for a long period of time can be harmful.
Vitamin A promotes healthy vision (especially night vision), growth and health of cells and tissues, bone growth, and tooth development. Vitamin A also helps protect you from infection by keeping mucous membranes in your mouth, stomach, intestines, respiratory, and urinary tracts healthy. Vitamin A also acts as a powerful antioxidant in the form of beta-carotene.
There are several forms of vitamin A. Retinol is a form that is found in animal foods. It is readily available to the body and is known as preformed vitamin A. Another form of vitamin A is a group called carotenoids, which includes beta-carotene. Beta-carotene is the carotenoid most readily converted by the body to vitamin A. Beta-carotene is found in plant foods that are orange, red, and dark yellow, and in some that are dark green. These forms are known as building blocks or provitamin forms of vitamin A.
Because vitamin A can be stored in the body, very large intakes over an extended period of time can be harmful. This is only true for preformed vitamin A. Vitamin A toxicity is almost always the result of high supplement intake and not from food. Your body converts beta-carotene to vitamin A only when the body needs it, so beta-carotene is not toxic in any amount. A significant deficiency of vitamin A can cause night blindness and other eye problems, dry and scaly skin, reproductive problems, and poor growth. Too much vitamin A (retinol) can lead to headaches, dry and scaly skin, bone and joint pain, liver damage, vomiting, loss of appetite, abnormal bone growth, nerve damage, and birth defects.
When taking a supplement, make sure you are not taking more vitamin A (retinol) than you need for your age range and gender. You will find a breakdown of vitamin A into beta-carotene and retinol on most supplement labels. Even though beta-carotene is not toxic to the body, it is not recommended to take megadoses through supplements. Vitamin A has a UL set at 3,000 micrograms (mcg) or 10,000 IU (international units) per day for adults over eighteen. This is the highest daily recommended intake of vitamin A that is unlikely to pose risks of adverse health effects.
Foods rich in vitamin A (retinol) include beef liver, eggs, milk fortified with vitamin A, other vitamin A-fortified foods, fish oil, margarine, and cheese. Foods rich in vitamin A (beta-carotene) include sweet potatoes, carrots, kale, spinach, apricots, cantaloupe, broccoli, and winter squash.
ALERT! Women who are pregnant should be especially cautious about taking too much vitamin A through supplements. Studies show that some women who take large doses of vitamin A near the time of conception or early in the pregnancy run a much higher than average risk of delivering an infant with birth defects.
Vitamin D promotes the absorption and use of two minerals: calcium and phosphorus. It helps deposit these two minerals in bones and teeth, making them stronger and healthier. The body can get vitamin D from two sources: food and the sun. This vitamin is known as the "sunshine vitamin" because the body can make vitamin D after sunlight hits the skin. The body's ability to produce vitamin D from sunlight diminishes with age; therefore, requirements increase for older adults.
Not getting enough vitamin D throughout life can cause osteoporosis (or brittle bone disease) later in life. Low levels of vitamin D can also increase the risk of bone softening, known as osteomalacia, in older adults. A deficiency of vitamin D in children can lead to rickets, or defective bone growth. With the vitamin D fortification of milk, the incidence of rickets has been basically wiped out in the United States.
Because vitamin D is a fat-soluble vitamin, it can be toxic in larger doses. Toxicity can lead to kidney stones or damage, weakened muscles and bones, excessive bleeding, and other health problems. Levels high enough to cause health complications usually come from supplements, not from food or too much sunlight. If you take a supplement that includes vitamin D, make sure it does not contain more than you need for your age range and gender. Vitamin D has a UL set at 50 mcg or 2,000 IU per day for children and adults. There is no UL established for infants.
Foods rich in vitamin D include fortified milk, cheese, egg yolks, salmon, margarine, mackerel, canned sardines, and fortified breakfast cereals.
Vitamin E's main function in promoting health is as a powerful antioxidant. As such, this vitamin helps protect body cells from oxidation, which leads to cell damage. As an antioxidant, vitamin E may affect aging, infertility, heart disease, and cancer. The mineral selenium enhances the antioxidant capabilities of vitamin E. Recent studies have also shown that vitamin E may play a role in reducing muscle inflammation and soreness after vigorous exercise sessions.
Vitamin E is actually a group of substances called tocopherols. All of these tocopherols possess different potencies. For this reason you will often see vitamin E measured in milligrams (mg) of alpha-tocopherol equivalents.
Vitamin E is very abundant in our food supply, so a deficiency is quite rare. Vitamin E is considered nontoxic, even over RDA levels. Vitamin E has a UL set at 1,000 mg per day for adults over eighteen.
Foods rich in vitamin E include dried almonds, vegetable oils, salad dressing, nuts and seeds, wheat germ, peanut butter, and green leafy vegetables.
Vitamin K's primary function is to help make a protein, known as prothrombin, which is necessary for helping blood to clot. It also aids the body in making some other body proteins for blood, bones, and kidneys. Vitamin K is unique in that, as well as being obtained from the diet, it is also made in the body, from bacteria in the intestines.
A deficiency of vitamin K is unlikely except in connection with rare health problems. The prolonged use of antibiotics may tend to cause problems, because they destroy some bacteria in your intestines that help to produce vitamin K. There have been no reported problems in ingesting excess amounts of vitamin K, though moderation is still the best policy. Vitamin K has no established UL.
ALERT! People who take various types of blood-thinning medications or anticoagulants should consume foods containing vitamin K in moderation. If you take these types of medications, ask your doctor about vitamin K intake.
Foods rich in vitamin K include turnip greens, green leafy vegetables like spinach or kale, broccoli, cabbage, beef liver, egg yolk, and wheat bran or wheat germ.
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Copyright © 2002 by Kimberly A. Tessmer. Excerpted from The Everything Nutrition Book: Boost Energy, Prevent Illness, and Live Longer with permission of its publisher, Adams Media Corporation.
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