Healthy Eating: Valuable Vitamins
A healthy diet consists not only of optimal portions of macronutrients, but also recommended levels of essential micronutrients. Micronutrients include vitamins and minerals. It is important to recognize whether you are getting what your body needs, and to make necessary changes in your daily diet if you are not. What Are Vitamins?
Vitamins are natural substances that are necessary for almost every process in the body. Micronutrients help trigger thousands of chemical reactions essential to maintaining good health. Most of these reactions are linked because one triggers another. A missing vitamin or a deficiency of a certain vitamin anywhere in the linked chain can cause a collapse, with health problems being the result.
Vitamins are organic compounds (or compounds that contain carbon), which are required in small amounts and are necessary to promote growth, health, and life. Vitamins are produced by living material such as plants and animals. Most vitamins are not made by the body in sufficient amounts to maintain health, so they must be obtained through a person's diet. Vitamins are classified into two groups: fat-soluble and water-soluble.
Vitamins are labeled as "micro" nutrients because they are needed in only small amounts to do their jobs properly. Don't let the word "micro" fool you, though; good things come in small packages! The micronutrients are just as essential as the macronutrients in helping to keep your body functioning properly.
What are antioxidants? When cells burn oxygen, they form free radicals. Free radicals can damage body cells, tissue, and DNA, which could lead to the onset of chronic health problems. Certain environmental factors can also cause free radicals. Antioxidants are vitamins that counteract the effects of these harmful free radicals.
Unlike macronutrients, vitamins do not provide calories or supply direct energy, but they do assist the calories in carbohydrates, proteins, and fats to produce energy. Consuming the macronutrients (carbohydrates, proteins, and fat) supplies the thirteen vitamins that the body requires. Vitamins are found in a wide variety of foods, with some foods being better sources than others. For this reason, eating a wide variety of foods ensures a better intake of vitamins.
Dietary Reference Intakes (DRIs)
Before learning why each vitamin is important and how much you need, it is crucial to understand how these values are generated. In the United States, the Food and Nutrition Board of the National Academy of Sciences/National Research Council is responsible for establishing and updating nutrition guidelines. The Recommended Dietary Allowances, or RDAs, have always been the benchmark for adequate nutritional intake in the United States. The RDAs are based on scientific evidence. They reflect the amount of a nutrient that is sufficient to meet the requirement of 97 to 98 percent of healthy individuals in a particular life stage and gender group. Because scientific knowledge of the relationship between nutrition and health has broadened so much, the Food and Nutrition Board partnered with Health Canada in the late 1990s. Together, the agencies developed a new approach called Dietary Reference Intakes (DRIs).
The DRIs represent an approach that serves to optimize health instead of just preventing nutritional deficiencies, as the RDAs have. The DRIs include RDAs as goals for intake by individuals, but also incorporate three new types of reference values. Where adequate information is available, each nutrient will have a set of DRIs. Each group of nutrients is presently being studied individually. Eventually, DRIs will replace RDAs in the United States and RNIs (Recommended Nutrient Intakes) in Canada.
The DRIs incorporate an average of three types of reference values:
- Estimated Average Requirement (EAR)
- Recommended Dietary Allowance (RDA) or Adequate Intake (AI)
- Tolerable Upper Intake Level (UL)
Fat-Soluble Vitamins
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
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
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
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
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.
Water-Soluble Vitamins
Unlike the fat-soluble vitamins, water-soluble vitamins dissolve in water. These vitamins are carried in the bloodstream and, for the most part, are not stored in the body. In general, your body uses what it needs and excretes the rest through urine. For this reason, it is important to regularly replenish these vitamins by eating a healthy and varied diet each day. Because water-soluble vitamins dissolve in water, they are much more easily destroyed in cooking and storing than the fat-soluble vitamins are.
The water-soluble vitamins consist of the B-complex vitamins and vitamin C. The B vitamins work together in converting carbohydrates, protein, and fats to energy, and many are found in the same foods. For this reason, poor intake of one B vitamin is usually associated with poor intake of other B vitamins.
Thiamine (Vitamin B1)
Thiamine is needed to help produce energy from the carbohydrates that you eat. It also is required for normal functioning of all body cells, especially nerves.
A deficiency of thiamine can lead to beriberi, fatigue, mental confusion, loss of energy, nerve damage, muscle weakness, and impaired growth. Thiamine deficiency is very rare in the United States because most people consume plenty of grain products. Since thiamine is a water-soluble vitamin, the body excretes excess amounts that you consume. There are no known benefits to taking megadoses of thiamine, including the popular belief that it will help boost energy. Thiamine has no established UL.
Foods rich in thiamine (vitamin B1) include whole-grain foods, enriched-grain foods, fortified cereals, beef liver, pork, and wheat germ.
Fact: When whole grains are refined, certain vitamins, including the B vitamins, are lost during the milling process. Refined grains are therefore enriched, meaning that nutrients—including B vitamins—are added back to the grain.
Riboflavin (Vitamin B2)
Just like thiamine, riboflavin plays a key role in releasing energy from the macronutrients to all cells of the body. Riboflavin also helps change the amino acid (building blocks of protein) tryptophan into niacin, another B vitamin. Riboflavin is important in normal growth, production of certain hormones, formation of red blood cells, and in vision and skin health.
A deficiency of riboflavin is unlikely, but can cause eye disorders, dry and flaky skin, and burning and dryness of the mouth and tongue. There are no reported problems from consuming too much, but again, moderation is the best policy. Riboflavin has no established UL.
Foods rich in riboflavin (vitamin B2) include beef liver, milk, low-fat yogurt, cheese, enriched-grain foods, whole-grain foods, eggs, and green leafy vegetables.
Fact: Riboflavin is easily destroyed by light. For this reason, milk is packaged in opaque plastic or cardboard containers. Riboflavin-rich foods should be stored in darker places and not in transparent containers such as glass.
Niacin (Vitamin B3)
This B vitamin, like its counterparts, is also involved in releasing energy from foods. Niacin specifically helps your body use sugars and fatty acids. In addition, niacin helps enzymes function normally in the body and promotes the health of nerves, skin, and the digestive system.
Although niacin deficiency is rare among populations that eat adequate amounts of protein-rich foods, it can cause pellagra. Symptoms include diarrhea, mental confusion, and skin problems. Niacin, in large doses, has been used as a cholesterol-lowering supplement. Because large doses can cause symptoms such as flushed skin, rashes, and even liver damage, this should only be done under doctors' supervision. Niacin has a UL set at 35 mg per day for adults over eighteen.
Niacin is usually measured in niacin equivalents ONE) because it comes from two sources: niacin itself and from the amino acid tryptophan. Tryptophan can be converted to niacin in the presence of riboflavin and of vitamin B6. Foods rich in niacin include meat, poultry, fish, legumes, peanut butter, enriched and fortified grain products, and yogurt.
Pyridoxine (Vitamin B6)
Vitamin B6 is necessary in helping your body to make nonessential amino acids (the building blocks of protein). These nonessential amino acids are used to make necessary body cells. Vitamin B6 also helps to turn the amino acid tryptophan into niacin and serotonin (a messenger in the brain). This vitamin also helps produce insulin, hemoglobin, and antibodies that help fight infection.
Deficiency symptoms of vitamin B6 include depression, nausea, and greasy and flaky skin. In infants, a deficiency can cause irritability and mental convulsions in severe cases. Proper amounts of breast milk and properly prepared infant formulas contain enough of this vitamin to protect against deficiencies. Vitamin B6 is one of the few water-soluble vitamins that can cause harm if taken in megadoses. Large doses taken over a long period can damage the nervous system. Vitamin B6 has a UL set at 100 mg per day for adults over eighteen.
Foods rich in vitamin B6 include protein-rich foods such as chicken, fish, pork, liver, peanut butter, whole grains, nuts, and legumes.
Cobalamin (Vitamin B12)
Vitamin B12 works closely with folic acid to form red blood cells. It also helps maintain the nervous system and is essential for the normal functioning of all body cells. Vitamin B12 is necessary in assisting the body to use fat and some amino acids.
A deficiency of vitamin B12 can result in anemia, fatigue, nerve damage, smooth tongue, and very sensitive skin. It is important to know that a deficiency of this vitamin can be hidden, and even progress, if extra folic acid is taken to treat or prevent anemia.
ALERT! Since B12 is found mostly in animal products, strict vegetarians and infants are at risk of developing a B12 deficiency. Including fortified foods and/or dietary supplements daily can help prevent this.
The classic deficiency symptom of vitamin B12 is anemia. This vitamin cannot be absorbed without the help of a substance called the intrinsic factor. Because this intrinsic factor is made in the lining of the stomach, the elderly and people with gastrointestinal disorders may not absorb the vitamin B12 their body needs. There are also people who, for either medical or genetic reasons, are missing this intrinsic factor. This problem can usually be treated with B12 injections. When anemia is caused by a lack of the intrinsic factor, it is called pernicious anemia. When the anemia is caused by poor dietary intake, it is called macrocytic anemia. Because of the body's ability to store vitamin B12, and because of the small amount needed daily, a deficiency can take years to develop. There are no known toxic effects of taking large doses of vitamin B12, but neither is there any scientific evidence that extra vitamin B12 helps boost energy. Vitamin B12 has no established UL.
Foods rich in vitamin B12 include meat, fish, poultry, eggs, milk and other dairy foods, and fortified foods.
Folic Acid (Folacin or Folate)
Folic acid's main role is to maintain the cell's genetic code—DNA, the master plan for cell reproduction. It also works with vitamin B12 to form hemoglobin in red blood cells.
In recent years, folic acid has gained much attention for its role in reducing the risk for neural tube birth defects, such as spina bifida, in newborn babies. The embryo's neural tube is what becomes the spinal cord. It is vital that pregnant women or women of childbearing years consume enough folic acid through food and supplements, especially during the first trimester. Other deficiencies of folic acid include anemia, impaired growth, and abnormal digestive function. Taking too much folic acid through supplements can mask a vitamin B12 deficiency and could interfere with other medications. In the synthetic form—the form used to fortify foods and in supplements—folic acid has a UL of 1,000 mcg per day for adults over eighteen.
Fact: Most enriched-grain products now have to be fortified with folic acid, according to a new FDA regulation. This is to help ensure that women get enough folic acid to help prevent neural tube birth defects during pregnancy.
Foods rich in folic acid include some fruits, such as oranges, as well as leafy vegetables, legumes, liver, wheat germ, some fortified cereals, avocados, and enriched-grain products.
Biotin
Biotin participates in the metabolism of the macronutrients for energy and helps your body produce energy in the cells. For people who eat a healthy, well-balanced diet, deficiency is not a problem. In the rare cases when deficiency does occur, symptoms include heart abnormalities, loss of appetite, fatigue, depression, and dry skin. Biotin has no known toxic effects and no established UL.
This vitamin is found in a wide variety of foods, such as eggs, liver, yeast breads, cereals, wheat germ, and oatmeal.
Pantothenic Acid
Like biotin, pantothenic acid also participates in the metabolism of the macronutrients for energy and helps your body produce energy in the cells. In addition, pantothenic acid functions in the production of some hormones and neurotransmitters in the brain.
Deficiency is rare in those who eat a healthy, well-balanced diet. When deficiency does occur, symptoms include nausea, fatigue, and difficulty sleeping. The only possible effects of consuming too much pantothenic acid are occasional diarrhea and water retention. Pantothenic acid has no established UL.
Foods rich in pantothenic acid include meat, poultry, fish, whole-grain cereals, legumes, yogurt, sweet potatoes, milk, and eggs.
Vitamin C (Ascorbic Acid)
Vitamin C is often associated with warding off the common cold. There is no conclusive data that large doses of vitamin C prevent colds; they may reduce the severity or duration of symptoms, but there is no definitive evidence. Scientific evidence does not suggest taking large doses of vitamin C on a regular basis to boost immunity or to decrease risks for the common cold.
But vitamin C does have some very important functions. Vitamin C produces collagen, a connective tissue that holds muscles, bones, and other tissues together. It also helps form and repair red blood cells, bones, and other tissue; helps protect you from bruising by keeping capillary walls and blood vessels firm; helps keep your gums healthy; helps heal cuts and wounds; and helps keep your immune system strong and healthy. Vitamin C helps your body absorb iron from plant sources, which is not as easily absorbed as iron from animal foods. Vitamin C is one of the very powerful antioxidants. As an antioxidant, vitamin C attacks free radicals in the body's fluids.
Essential: Cigarette smokers need at least twice as much vitamin C as nonsmokers, that is, at least 100 milligrams per day.
Since vitamin C is so widely available in our foods, deficiency is rare. Possible deficiency symptoms include poor wound healing, higher susceptibility to infections, bleeding gums, hemorrhaging, and, in severe cases, scurvy. Scurvy is a disease characterized by bleeding and swollen gums, joint pain, muscle wasting, and bruising.
Because vitamin C is a water-soluble vitamin, your body excretes the excess that may be consumed. Very large doses, though, could cause kidney stones, nausea, and diarrhea. The effects of taking large amounts over extended periods of time are not yet known. Vitamin C has a UL set at 2,000 mg per day for adults over eighteen.
Most fruits and vegetables are great sources of vitamin C. These include all citrus fruits, berries, melons, peppers, dark green leafy vegetables, potatoes (especially the skin), and tomatoes.
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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