Groups of nutrients that the human body needs in order to remain healthy and function normally.
Vitamins are organic substances, small amounts of which are needed for certain biochemical reactions in the human body. Minerals are inorganic compounds also needed for a variety of bodily functions.
Vitamins
Because the human body does not synthesize vitamins (at least not in the quantities needed), they must be obtained either through food or through nutritional supplements. Vitamins help the body use fats, proteins, minerals, and carbohydrates. They perform numerous functions, including fighting infections, maintaining mental alertness, helping with blood clotting, forming red blood cells, and promoting good vision. Although medical experts recommend obtaining one's necessary allowance of vitamins by eating a balanced diet, nutritional supplements are very popular among Americans, many of whom fear that their regular diets do not provide them with the nutrients they need to stay healthy. Over half of all Americans say they use vitamin supplements on a daily basis. There are 13 known vitamins, which can be divided into two categories: fat-soluble and water-soluble. The fat-soluble vitamins—A, D, E, and K—dissolve in fat but not in water. After being absorbed, they are stored by the body, creating reserves that can be called upon when needed. However, because they are fat-soluble, these vitamins also pose a relatively high risk of toxicity if taken in large amounts.
Vitamin A occurs in two forms. Retinol, found in meat and dairy products, can be used immediately, while beta-carotene, found in plants, must be converted to vitamin A in the body. Vitamin A is essential for proper vision and normal bone growth and also aids the immune and reproductive systems. Recent research has linked beta-carotene, once regarded as merely a raw material needed for vitamin A, to the prevention of vision disorders, cancer, cardiovascular disease, and other health problems. Beta-carotene is found in yellow and orange vegetables and green leafy vegetables. Animal products containing vitamin A include milk, cheese, butter, egg yolks, fish, and liver.
Unlike other vitamins, vitamin D can be synthesized by the body. Ultraviolet light activates the manufacture of this vitamin by the skin. With enough exposure to the sun, people can manufacture as much vitamin D as they need. This vitamin helps the body absorb calcium and phosphorus, helps the pancreas produce insulin, and plays a role in the immune system. Foods are not an important natural source of vitamin D, although some fish, dairy, and meat products contain amounts of vitamin D. The main dietary sources for this vitamin are foods that have been artificially fortified.
Vitamin E is one of a group of vitamins called antioxidants that have received a great deal of attention in recent times (the other antioxidants are vitamin C and bet-acarotene). Antioxidants protect cells from damage by free radicals, substances produced whenever the body uses oxygen. Researchers have claimed that antioxidants protect against chronic disease, including cancer, cardiovascular disease, and cataracts, as well as aging. Besides being an antioxidant itself, vitamin E also protects the body's supply of the antioxidants vitamin C and beta-carotene. Vitamin E is found in vegetable oils, wheat germ, whole grains, and green leafy vegetables. Although vitamin E deficiency is very rare in the United States, premature or low birth-weight babies tend to have low levels of this vitamin, and physicians sometimes recommend vitamin E supplements in these cases.
Vitamin K is important for blood clotting and is thought to be necessary for bone formation. Newborn babies are routinely given vitamin K to prevent abnormal bleeding. This vitamin is found in meat, dairy products, and green leafy vegetables. Because the intestines play a role in the production of vitamin K, people with gastrointestinal disorders have an above average likelihood of being deficient in this vitamin.
The water-soluble vitamins are vitamin C and those belonging to the B complex—B1 (thiamin), B 2 (riboflavin), B 3 (niacin), B 5 (pantothenic acid), B 6 (pyridoxine), B 12 (cyanocobalamin), biotin, and folie acid. These vitamins dissolve easily in water and are only stored in the
body in small quantities (surpluses of these vitamins are eliminated in the urine). While water-soluble vitamins pose less danger of toxicity than fat-soluble ones, it is easier to develop deficiencies of these vitamins.
Vitamin C (ascorbic acid) has long been touted as a remedy for the common cold due to its role in strengthening the immune system, but it also performs many other functions to keep the body healthy. It helps in the processing of carbohydrates and the production of fats and proteins, promotes healing, aids in the formation of connective tissue, and stimulates production of certain hormones and brain chemicals. In addition, it is one of the antioxidants that protect the body from damage by free radicals. Vitamin C is often recommended for maintaining health in times of stress. It is found in citrus fruits, strawberries, melons, and other types of fruit, as well as green vegetables, tomatoes, potatoes, and, in more modest amounts, in meat, fish, and dairy products. It is present in greater quantities in fresh vegetables than cooked ones.
The eight vitamins of the B complex aid the body's metabolism, often with two or more of them working together. All are relatively non-toxic because they are water-soluble. Common functions of several B vitamins include maintaining the nervous system, providing energy, and assisting in the production of red and white blood cells. Each individual B vitamin also performs a variety of special functions, from B 1 (thiamin), which removes excess lactic acid from the body, to folic acid, which aids in fetal and infant development. Niacin (vitamin B 3) has gained popularity due to research showing that it can help control blood cholesterol levels. Certain types of food are rich sources for several of the B vitamins: meat (especially organ meat such as liver and kidney), poultry, fish, wheat germ, yeast, and, in some cases, legumes (soybeans and peas), spinach, and dairy products.
Minerals
Although vitamins generally receive more attention than minerals, the body actually needs larger amounts of certain minerals—called macrominerals—than the amounts of vitamins it requires to stay healthy. The seven macrominerals, all required in amounts of 100 mg or more a day, are calcium, magnesium, phosphorus, sodium, potassium, chloride, and sulfur. In addition, there are 10 microminerals, also called "trace elements," of which the body requires only very small amounts. These are cobalt, iron, zinc, iodine, copper, fluorine, manganese, chromium, selenium, and molybdenum. In spite of the small requirements for these minerals—in some cases considerably less than 1 mg—they are all needed if good health is to be maintained.
Iron, which plays an important role in carrying oxygen to the tissues, has long been the mineral best known to the general public because of its connection with anemia. Iron-fortified, multivitamin supplements have been popular for decades. Women are especially at risk for iron deficiency because iron is lost during menstruation, especially by women who bleed heavily. Good dietary sources of iron are red meat, liver, dark green leafy vegetables, and legumes. In addition, many foods are fortified with iron.
Calcium, which is necessary for healthy bones and teeth, is the body's most plentiful mineral, accounting for about 2% of the average person's body weight. This mineral is also needed for muscle contraction, blood clotting, and the release of neurotransmitters, which carry impulses throughout the nervous system. The main dietary sources of calcium are dairy products. Other good sources of calcium are green leafy vegetables, beans, and nuts. Many foods, including orange juice, breakfast cereal, and bread, are available fortified with calcium.
Zinc is an important mineral found in all the cells of the body. It is necessary for normal physical growth in children and is also known for promoting healing and fighting infections. Zinc deficiencies in pregnant women can interfere with normal fetal development. Animal products—especially meat and seafood—are the main dietary source of zinc. Magnesium, which activates over 300 of the body's enzymes, is needed for muscle relaxation. It is thought to reduce hypertension and lessen the damage from heart attacks. Selenium, another important mineral, is an antioxidant believed capable of preventing heart attacks and reducing the risk of certain types of cancer.
Children's vitamin and mineral requirements
The American Academy of Pediatrics recommends that children obtain the vitamins they need by eating a well-balanced diet rather than through nutritional supplements. The group has stated that "healthy children receiving a normal, well-balanced diet should not need vitamin supplements over and above the recommended dietary allowances." However, some physicians still recommend vitamins for children until they are eating solid foods.
Infancy. Low birth-weight babies (those weighing less than 5.5 lb [2.5 g]) may require supplements due to vitamin deficiencies. Newborn babies generally have low levels of vitamin K, and it is standard practice for physicians to provide injections of this vitamin. Physicians may recommend vitamin supplementation in infancy during periods of rapid growth, or due to certain dietary factors, such as the use of powdered milk or goat's milk. Vitamins A and D are often recommended for breast-fed babies. Because they go through periods of rapid growth, infants also have aspecial need for iron. Babies are born with reserves of iron, which are enhanced by natural iron from breast milk or iron supplements in formula. By the
age of six months, the infant's diet should include cereal, meat, and other foods that contain iron. Physicians routinely test hemoglobin levels in infants at the age of nine months to check for anemia.
School age. Some experts believe that supplements can be beneficial for older children since many may not eat well-balanced diets, either because their parents do not provide them or because the children are finicky eaters. Supplements are often recommended for children on weight-reduction diets. Children in strict vegetarian families who do not receive animal protein from dairy products may have a greater than average need for vitamin supplements, especially vitamin B12. Other situations that may make nutritional supplements necessary include dietary restrictions due to food allergies, and metabolic or other disorders. A study conducted at the University of Washington in Seattle and published in the Journal of the American Dietetic Association found that children between the ages of 3-½ and 9 are most likely to be deficient in folie acid and vitamin B 6. Iron and zinc—trace elements that promote normal growth—have also been cited as nutrients lacking in the diets of many children. All experts who recommend supplements emphasize the fact that in almost all cases they should be considered as insurance rather than as a substitute for an adequate diet.
Adolescence. Due to the rapid growth spurts and the bad eating habits that are common at this age, adolescents may develop some vitamin deficiencies. Teenage girls, in particular, may be deficient in iron.
Nutritional supplements
The benefits of many nutritional supplements for children are compromised by the fact that they contain refined sugar or artificial sweeteners. It is possible to find alternatives to these products, especially in health food stores, which often carry liquid vitamin formulas sweetened with honey or rice syrup. Nutritional supplements are best administered with meals (usually afterward, except in the case of a purely mineral supplement, which should be given before). Parents need to treat nutritional supplements with the same caution as other pills in the household, as an accidental overdose can be serious or even fatal, especially when it involves supplements that contain iron.
Adverse reactions have been reported for the following vitamins in the dosages listed: vitamin A (over 25,000 international units [IU] or more daily for several months); vitamin B 6 (200-500 mg daily for several months); vitamin C (doses above 1,000 mg daily for long periods of time); vitamin D (more than 5,000 IU a day for several weeks); and zinc (more than 20 mg a day for over a month).
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