What are vitamins and minerals?

Structure and Functions

Vitamins are organic compounds (that is, compounds made up of carbon, oxygen, nitrogen, sulfur, or hydrogen) that are constituents of food and that are crucial to the maintenance of life and good health. They make possible the production of energy and the formation of coherent body tissues from the macronutrients normally consumed in a regular diet. They are, among other things, coenzymes that serve as oxidizing, reducing, and transfer chemicals at the active sites of enzymes. Vitamins are part of the one hundred or so organic compounds that are of the proper size and stability to be absorbed from the digestive tract into the bloodstream without digestion or breakdown. Nevertheless, they are not produced in the body in amounts large enough to keep a person healthy—because they have always been available in food, there was probably no need for the human metabolism to produce them. Vitamins are synthesized by plants, and therefore plants constitute the principal natural source of these
compounds.

Vitamins are divided into two main groups: the water-soluble and the fat-soluble vitamins. Structural differences account for the two types of solubility. Fat-soluble vitamins (such as vitamins A, D, E, and K) consist mainly of hydrocarbon groupings (nonpolar hydrocarbon chains and rings compatible with nonpolar oil and fat) and are structurally similar to fats, whereas water-soluble vitamins have polar hydroxyl (-OH) and carboxyl (-COOH) groups that are attracted to and form hydrogen bonds with water. One of the most important differences between vitamins is the result of their solubility: Fat-soluble vitamins are stored in the body tissues and organs for relatively long periods of time, while water-soluble vitamins are eliminated from the body in a relatively fast manner, sometimes in a matter of hours.

Vitamin A (retinol) maintains the health of eyes, skin, and mucous membranes and is particularly important for good vision in dim light. There are various physiological equivalents to vitamin A, that is, compounds with closely related structures that can be used as the vitamin itself. Beta carotene is a provitamin (a substance that can be easily converted to a vitamin) of vitamin A found in carrots. The vitamin can also be found in liver and liver oils. Lack of vitamin A can cause night or total blindness.

The B vitamins are often considered as a group, called the B complex, because they work together as coenzymes in biochemical reactions leading to growth and energy production. They are water soluble and easily eliminated from food in the cooking process. Members of this group include pyridoxine (B6), involved in at least sixty enzyme reactions (mostly in the metabolism and synthesis of proteins); thiamine (B1), a coenzyme in carbohydrate metabolism and involved in energy production, digestion, and nerve activity; riboflavin (B2), used in obtaining energy from foods; pantothenic acid (B3), needed for proper growth; niacin (B4), needed for the production of healthy tissues; cobalamin (B12), involved in the production and growth of red blood cells; and folic acid (B9), also involved in the production of red blood cells and in metabolism. They are present in various foods, especially
meat and dairy products. Deficiency symptoms include anemia, skin disorders, and nervous system disorders.

Vitamin C, or ascorbic acid, is involved in the destruction of invading bacteria, in the synthesis and activity of interferon (which prevents entry of viruses into cells), in decreasing the effect of toxic substances (such as drugs and pollutants), and in the formation of connective tissue. Humans are one of the few species of animals for which ascorbic acid is actually a vitamin, since other species produce it in their metabolic processes. Deficiency symptoms include the degeneration of tissue and scurvy. Vitamin C is found mostly in citrus fruits.

Vitamin D (calciferol) promotes the absorption of calcium and phosphorus through the intestinal wall and into the bloodstream. Its deficiency induces the disease
rickets and, in adults, the malformation of bones. Unlike other vitamins, it forms in the body through the action of the sun’s ultraviolet light. As with the vitamin B complex, vitamin D has a set of closely related molecular structures, called D1, D2, D3, and so on. All these structures have the same physiological function. Because of limited sun exposure, copious clothing, and indoor living and working conditions, humans need to add vitamin D to their diet, as in fortified milk, cod liver oil, or vitamin supplements.

Vitamin E (alpha tocopherol) is an antioxidant of polyunsaturated fatty acids (fatty acids with numerous double bonds). These fatty acids readily form peroxides, which are particularly damaging because they can lead to runaway oxidation in cells. Vitamin E protects the integrity of cell membranes, which contain considerable amounts of fat. It also helps maintain the integrity of the circulatory and central nervous systems; is involved in the functioning of the kidneys, lungs, liver, and genitalia; and detoxifies poisonous materials absorbed by the body. Since aging, in some theories, is considered to be the cumulative effect of free radicals (reactive atoms) running wild in the body, the antioxidant properties of vitamin E may make it a good candidate for inhibiting aging, or at least preventing premature aging. Its deficiency symptoms in humans are unknown. Vitamin E is present in various foods, especially in grain oils.

Biotin (also called vitamin H) participates in metabolism by acting as a carboxyl carrier for a number of enzymes. Its sources are liver, cereals, and egg yolks. Symptoms of deficiency include
alopecia (the loss or absence of hair) and skin rashes.

Vitamin K completes the list of vitamins. It participates in the clotting of blood, and its deficiency can cause hemorrhage and liver damage. This vitamin is commonly found in plants and vegetables.

The term “minerals,” when used in a nutritional context, includes all the nutritional chemical elements of foods obtained from macronutrients, except for carbon, hydrogen, nitrogen, oxygen, and sulfur. This term also refers to metal elements combined with others in compounds such as soluble inorganic salts. It is in this combined form that they serve indispensable functions in the body.

Minerals pass slowly through the body and are excreted in the feces, urine, and sweat. Therefore, they must be replaced and an appropriate balance continuously maintained. Because living beings cannot generate minerals in their own bodies, they must obtain them from foods or food supplements. Plants pick up minerals directly from the soil, and animals get them from the plants that they ingest. As opposed to vitamins, which are synthesized by plants, minerals cannot be generated if they are not in the soil. Among their many functions, minerals are components of enzymes, are structural components of body parts such as bones, are involved in maintaining the electrolyte balance in body fluids, and transport materials, as hemoglobin does in blood.

There are seventeen known minerals, although many others may exist. Since most of them are present in the body in relatively small amounts, their functions have been determined through the symptoms of various dietary deficiencies. Minerals can be grouped into two classes. The major elements—calcium, phosphorus, and magnesium—are required in amounts of 1 gram or more per day. The trace elements, such as chlorine, chromium, cobalt, copper, fluorine, iodine, iron, manganese, molybdenum, nickel, selenium, sulfur, vanadium, and zinc, are needed in milligram or microgram quantities each day.

Calcium, probably the best-known mineral, is present in the body in a greater amount than any other mineral: up to 1.5 or 2.0 percent of total body weight, with 99 percent of it in bones and teeth. In the nervous system, it is used to slow down the heartbeat, and it is metabolized in the body by a hormone synthesized from calciferol (vitamin D). Excess calcium can give rise to kidney stones. Its deficiency is common in postmenopausal women, who produce less estrogen. This decrease encourages bone dissolution, and when bones are dissolved, calcium is lost. Calcium is found in milk and dairy products, fish, and green vegetables. Phosphorus, the second most common mineral, is a structural component of bones and soft tissue. It is found in nearly all foods.

Sodium and potassium cations (positively charged atoms) are components of many minerals. They work in the conservation of electrolytic balance in cell fluids. Potassium governs the activity of many cellular enzymes, while sodium keeps the water content of cellular fluids in a healthy balance. For the body to work properly, it needs the appropriate ratio of sodium to potassium. Potassium ions concentrate inside the cell, while sodium ions concentrate outside the cell. Natural unprocessed foods have high sodium-to-potassium ratios. Because sodium and potassium compounds are very soluble in water, however, they dissolve during processing and cooking and are discarded. Sodium is replenished by adding salt to food, but this is not the case with potassium, which is not added to food. Care must be taken in this matter, either by eating more fresh foods or by using a specialized table salt that contains a mixture of sodium chloride and potassium chloride. The retention of sodium leads to water retention and edema (swollen legs and ankles) and to high blood pressure in some
individuals. Sodium is mostly found in table salt, and potassium is found in meat, dairy products, and fruit.

Magnesium and chloride ions are the most common minerals in cell fluids, as they regulate fluid balances and electrical charges. Magnesium controls the formation of proteins inside the cell and the transmission of electrical signals from cell to cell. Chloride is present in the stomach as hydrochloric acid, or stomach acid. Magnesium is found in whole-grain cereals, dried fruits, and leafy green vegetables, and chloride is found in table salt.

Trace elements work in various ways, with most of them incorporated into the structure of enzymes, hormones, and related molecules or acting in conjunction with vitamins. Among the trace elements, one of the more important ones is iron, which is a critical part of the hemoglobin molecule of red blood cells and is involved in oxygen transport. Fluoride, another trace element, helps harden the enamel of teeth to make them resistant to decay; zinc plays an important role in growth, the healing of wounds, and the development of male sex glands; and manganese is needed for healthy bones and a well-functioning nervous system. Iodine is involved in the proper operation of the thyroid gland, chromium is important in the metabolism of glucose, and cobalt aids in cell function. Copper and selenium are other trace elements needed by the body. Most trace elements are found in fish, meat, fruits, and vegetables.

Related Diseases

Vitamin deficiencies are not common in the United States and other Western countries. A well-balanced diet provides ample vitamins of all kinds. Megadoses of vitamins can create harmful effects, however, as a toxic dose exists for many vitamins. For example, vitamin A, when taken in excess, can cause headache, nausea, vomiting, fatigue, swelling, hemorrhage, pain in the arms and legs, and birth defects. An acute deficiency of the vitamin, however, can impair vision and eventually cause blindness. Consequently, there must be a balance in vitamin intake. This balance can be achieved by following the recommended daily (or dietary) allowances (RDAs).

In the United States, the Food and Nutrition Board of the National Academy of Sciences and the National Research Council determined the daily needs for some vitamins and minerals. The
Food and Drug Administration (FDA) made these findings the basis for its list of RDAs. These allowances are presented in units of grams or milligrams, and these amounts are determined using international units of biological activity. (Some vitamins come in several forms, all of which are physiologically equivalent.) RDAs do not cover every single vitamin and mineral needed for good health, nor do they cover the more extreme nutritional requirements that result from illness or unusual genetic makeup. They just serve as general guidelines for healthy individuals. For some substances lacking specific RDAs, such as chromium and a handful of other elements, the FDA lists the daily ranges of these micronutrients that it considers to be safe and effective. RDAs depend on gender, age, weight, and other conditions and are normally presented in food labels as percentages of the daily dietary requirement.

In 2005, the U.S. Department of Agriculture (USDA) updated the Food Guide Pyramid. The new pyramid emphasizes the need for physical activity (thirty minutes of moderate or vigorous exercise per day) and the importance of variety in diet. Consumers can get personalized recommendations, based on their age and gender, at MyPyramid.gov. Unlike the older food pyramids, the 2005 version suggests food quantities in cups and ounces, rather than as servings, which was ambiguous and confusing to consumers. For example, for a 2,000 calorie per day diet, the recommendations are six ounces of whole grains, two and a half cups of vegetables, two cups of fruit, three cups of dairy, and five and a half ounces from the meat and bean subgroup.

The main criticisms of the 2005 food recommendations are that they do not mention any specific foods from which to abstain, that people who do not have Web access cannot obtain personalized recommendations, and that the beef and dairy industry lobbies play a role in the USDA’s decisions about these matters. Consumers should keep in mind that the primary role of the USDA is to promote agriculture in the United States. Politics are embedded in decisions made about diets, and recommending that people eat less is not good for business. Some nutritionists and scientists believe that diet matters should be under the auspices of a more neutral party, such as the National Institutes of Health (NIH).

The activity of a vitamin or mineral depends only on its molecular structure, not on its source. Therefore, the synthetic vitamins found in food supplements provide the same nutrients as naturally occurring ones. It is crucial to remember, however, that other substances or nutrients are present in the food that is being consumed to obtain the necessary vitamin and mineral requirements. Authentic food often contains additional substances that enhance the absorption and utilization of its nutrients. For example, the calcium that is naturally present in food is more likely to carry with it any vitamin D or phosphorus that the body might need for its optimum use than is the calcium found in an antacid tablet or a food supplement. A balanced diet provides a diversity of nutrients that no pills can match.

The major medical use of the vitamins is in curing the deficiency diseases—that is, those caused by their absence from the diet. Nine vitamins have been judged by an FDA panel to be safe and effective as over-the-counter drugs. Supplementation is commonly thought of as a means of maintaining nutritional equilibrium in the body.

Many different analytical methods—such as ultraviolet-visible and infrared spectroscopy; paper, thin-layer, and gas-liquid chromatography; and mass spectroscopy—as well as biological assays have been used for the detection and identification of vitamins. They have greatly helped to explain the complex structures of these compounds. These methods are also used in the determination of the vitamin content of a particular food item, providing the consumer with valuable nutritional information.

Perspective and Prospects

Vitamin deficiency diseases such as scurvy, beriberi, and pellagra have plagued the world at least since the existence of written records. The concept of a vitamin or “accessory growth factor” was developed in the early part of the twentieth century. In 1912, Casimir Funk, a Polish biochemist, isolated a dietary growth factor from the outer covering of rice grains and found that, when added to the food of those who had beriberi, it cured the disease. The factor was an organic compound called an amine (that is, a compound containing nitrogen combined with carbon and hydrogen). Funk coined the term “vitamine” (meaning “life-giving amine”) for the compound, which is now called thiamin or vitamin B1. In the next five decades, there was an exciting era of the isolation, identification, and synthesis of vitamins. It was soon found that these compounds were not all amines, and the term was changed to “vitamins.” As more information on the structure of vitamins was obtained, names changed from general ones (such as vitamin C) to more specific ones (such as ascorbic acid). These discoveries led to the availability of inexpensive
synthetic vitamins and to a dramatic reduction in overt vitamin deficiency disease.

Small amounts of vitamins are essential for good health, but the benefits of taking megadoses of certain vitamins to prevent or cure certain ailments are often debated. Even so, there is evidence that the use of high levels of vitamins can prevent or alleviate a number of diseases. Improvements in the analytical methods used in the detection and identification of vitamins have led to better and more sensitive detection limits for these compounds. The result has been increased knowledge of vitamins and minerals and their function.

In 2002, the American Medical Association endorsed the notion that adults should take a multivitamin daily. This reversed the organization’s long-standing antivitamin stance that vitamins were a waste of time and money for all people except pregnant women and for some people with chronic illnesses. The current recommendation, published in the Journal of the American Medical Association, acknowledges that vitamins may prevent some kinds of chronic diseases, such as heart disease, cancer, and osteoporosis.
Nevertheless, the efficacy and safety of regular intake of multivitamins remains a subject of debate in the medical community. In a 2013 book entitled Do You Believe in Magic?: The Sense and Nonsense of Alternative Medicine
, Dr. Paul Offit of the University of Pennsylvania cites several studies suggesting that regular intake of vitamin supplements increases risk of disease. However, critics like Dr. Dallas Clouatre of the American College of Nutrition argue that many vitamin studies rely on unscientific data—such as self-reporting through questionnaires.

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