Index

Chemical Structure of Vitamins and Minerals

Vitamins and minerals are nutrients required in very small amounts for essential metabolic reactions in the body. Some diseases caused by vitamin deficiencies, such as scurvy, have been recognized since antiquity, but it was only in the 20th century that systematic nutritional studies identified the chemical structures of many of these essential compounds. In 1913, Vitamin A was recognized for its importance in vision, and in 1932, Vitamin C was found to be necessary to prevent scurvy. The following paragraphs give some information about the most important vitamins and minerals.

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The term "minerals" is applied to chemical elements present in the ash of calcined tissue. Dietary minerals may be present in inorganic salts, or as part of carbon-containing organic compounds. For example, magnesium is present in chlorophyll, the pigment that makes plants green. Six minerals are required by people in gram amounts: sodium (Na), potassium (K), calcium (Ca), magnesium (Mg), phosphorus (P), and chlorine (Cl). Daily requirements range from 0.3 to 2.0 grams per day. Nine trace minerals (microminerals) are required by people in minute amounts: chromium (Cr), copper (Cu), iodine (I), iron (Fe), fluorine (F), manganese (Mn), molybdenum (Mo), selenium (Se), and zinc (Zn). There are additional requirements for cobalt (Co), but these are generally expressed in terms of the cobalt-containing vitamin B12. All trace minerals are toxic at high levels.

The term Dietary Reference Intake (DRI) is used to represent daily dietary reference values such as Adequate Intake (AI), Tolerable Upper Intake Level (UL), Estimated Average Requirements (EAR), Nutrient Reference Value (NRV), and Recommended Dietary Allowance / Intake (RDA / RDI).

Calcium
Calcium (Ca) is the most abundant mineral in the human body. More than 99% of total body calcium is stored in the bones and teeth. Calcium is also found in body fluids where its function is to regulate contractions of blood vessels and muscles. The requirement for calcium is greatest from puberty to maturity, when the body grows very quickly. Milk and dairy products are good sources of calcium.

Fluorine
Most of the body's fluorine (F) is contained in bones and teeth. The main source of fluoride is drinking water. Fluorine hardens tooth enamel and effectively prevents dental caries. Excessive fluorine in drinking water can accumulate in teeth and bones, causing fluorosis. Permanent teeth that develop during high fluorine intake have irregularly distributed chalky patches on the surface of the enamel which become stained yellow or brown, producing a characteristic mottled appearance.

Iodine
iodine (I) is primarily involved in the synthesis of two thyroid hormones, thyroxine and triiodothyronine. In adults, about 80% of the iodide absorbed is trapped by the thyroid gland.

Most environmental iodine occurs in seawater. People living far from the sea are at particular risk of deficiency. Salt fortified with iodide (typically 70 μg/g) helps ensure adequate intake (150 μg/day). Deficiency is rare in areas where iodized salt is used but common worldwide. Iodine deficiency develops when iodide intake is less than 20 μg/day. In mild or moderate deficiency, the thyroid gland hypertrophies to concentrate iodide in itself, resulting in goiter which is an enlargement of the thyroid gland visible as a swelling of the front of the neck. Excessive iodine consumption can lead to thyrotoxicosis, a condition resulting from high concentrations of thyroid hormones in the body which can result from eating foods that have very high amounts of iodine, such as kombu-type kelp or seaweed.

Iron
Iron (Fe) is a component of hemoglobin, myoglobin, and many enzymes in the body. Heme iron, contained mainly in animal products, is absorbed much better than nonheme iron, which accounts for over 85% of iron in the average diet. However, absorption of nonheme iron is increased when it is consumed with animal protein and vitamin C. The Recommended Daily Allowance (RDA) of iron is 8 milligrams for men and postmenopausal women; 18 mg per day for premenopausal women. Iron deficiency, which can cause anemia, is the most common nutritional deficiency in the world. It may result from inadequate iron intake or from malabsorption. Meat products are the best sources of dietary iron. Iron deficiency may be caused by improper vegan or ovo-lacto vegetarian diets. Chronic bleeding may also cause iron deficiency. Iron may accumulate in the body when a person is given repeated blood transfusions or takes an overdose of iron supplements. Excess iron is toxic and may damage the intestines and other organs, as well as cause vomiting and diarrhea.

Magnesium
Magnesium (Mg) has several important metabolic functions in the production and transport of energy. It is also important for the contraction and relaxation of muscles. Magnesium is involved in the synthesis of protein, and it assists in the functioning of some enzymes. Most dietary magnesium comes from nuts, cereals, and dark green, leafy vegetables which are rich in chlorophyll.

Manganese
Manganese (Mn) is necessary for healthy bone structure and is a component of several enzyme systems, including manganese-specific glycosyltransferases and phosphoenolpyruvate carboxykinase. Manganese is found in cereals and nuts. The adequate intake of manganese is 2 to 5 mg/day.

Molybdenum
Molybdenum (Mo) is a component of coenzymes necessary for the activity of xanthine oxidase, sulfite oxidase, and aldehyde oxidase. Sulfite oxidase catalyzes the transformation of sulfite to sulfate which is necessary for the metabolism of sulfur-containing amino acids, such as cysteine. Legumes such as lentils, beans, and peas are good sources of molybdenum. The Recommended Dietary Allowance (RDA) for adult men and women is 45 micrograms/day. The tolerable upper intake level is 2 mg/day.

Potassium
Potassium (K) maintains fluid volume inside and outside of cells, and acts to blunt the rise of blood pressure in response to excess sodium intake. The adequate intake of potassium is 4.5 grams per day for children 9 to 13 years old, and 4.7 grams per day for older persons. Potassium is generally found in fruits and vegetables, dried peas, dairy products, meats, and nuts. Potassium from supplements or salt substitutes can result in hyperkalemia and possibly sudden death if excess is consumed by individuals with chronic renal insufficiency (kidney disease) or diabetes.

Selenium
Selenium (Se) is a part of the enzyme glutathione peroxidase, which metabolizes hydroperoxides formed from polyunsaturated fatty acids. Selenium is also a part of the enzymes that deiodinate thyroid hormones. Generally, selenium acts as an antioxidant that works with vitamin E.  Deficiency of selenium causes Keshan disease which is a form of congestive cardiomyopathy. The RDA for selenium is 70 micrograms (mcg). The tolerable upper level of selenium is 400 mcg/day for adults based on the prevention of hair and nail brittleness and early signs of chronic selenium toxicity. Toxic effects have occurred when blood selenium concentrations reach a level corresponding to an intake of 850 mcg/day. Selenium is found in poultry, meats, fish, and nuts.

Sodium
Sodium (Na) is usually consumed as table salt (Sodium Chloride, NaCl). The Adequate Intake of 1.5 grams per day with an upper limit of 2.3 grams per day is calculated to meet the needs for sweat losses for individuals 8 years or older engaged in recommended levels of physical activity. Active people in humid climates who sweat excessively may need more than the Adequate Intake. The upper limit applies to healthy individuals without hypertension, but may be too high for persons with hypertension.

Zinc
Zinc (Zn) is contained mainly in bones, teeth, hair, skin, liver, muscle, leukocytes, and testes. Zinc is a component of several hundred enzymes, including many nicotinamide adenine dinucleotide (NADH) dehydrogenases, RNA and DNA polymerases, and DNA transcription factors as well as alkaline phosphatase, superoxide dismutase, and carbonic anhydrase. The Recommended Daily Allowance (RDA) of zinc is 11 milligrams for men, and 8 milligrams for women.. Good dietary sources of zinc include mollusks, such as oysters, and cereals.

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In developed countries, vitamin deficiencies result mainly from poverty, food fads, drugs, or alcoholism. Vitamin toxicity (hypervitaminosis) usually results from taking megadoses of Vitamin A, D, B6, or niacin. Vitamins may be fat soluble (vitamins A, D, E, and K) or water soluble (B vitamins and vitamin C). The B vitamins include biotin, folate, niacin, pantothenic acid, riboflavin, thiamin, pyridoxine, and B12. Vegans may develop vitamin B12 deficiency unless they consume yeast extracts or Asian-style fermented foods. Strictly vegetarian diets also tend to be low in calcium, iron, and zinc.

Biotin (Vitamin B7)
Biotin (Vitamin B7) acts as a coenzyme for carboxylation reactions essential to fat and carbohydrate metabolism. Adequate intake for adults is 30 μg/day. Liver, egg yolks, green vegetables, and whole grains are rich sources of biotin.

Folic Acid (Vitamin B9)
Folate, also called Vitamin B9, is involved in maturation of red blood cells and the synthesis of purines and pyrimidines which are required for development of the fetal nervous system. Adequate folic acid intake before conception and throughout the first trimester of pregnancy helps prevent certain brain and spinal cord defects such as spina bifida. Folate is absorbed in the duodenum and upper jejunum. The US recommended daily dose for folate is 400 μg and the upper limit is 1000 μg. Folate is essentially nontoxic. Deficiency produces megaloblastic anemia indistinguishable from that due to vitamin B12 deficiency. A deficiency of folate in old age significantly increases the risk of developing dementia. Folic acid is found in dried peas, dried beans, yeast, and leafy green vegetables such as spinach, endive, lettuce, and mustard greens.

Niacin (Vitamin B3)
Niacin (Vitamin B3 or nicotinic acid) derivatives include nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP), which are coenzymes in oxidation-reduction reactions vital in cell metabolism. Dietary niacin deficiency causes pellagra, a disease characterized by dermatitis, gastrointestinal disorders, and mental disturbances. Primary deficiency results from extremely inadequate intake of both niacin and the amino acid tryptophan, which usually occurs in areas where maize (Indian corn) constitutes a substantial part of the diet. Mushrooms and fish are good sources of niacin.

Pantothenic Acid (Vitamin B5)
Pantothenic acid (Vitamin B5) is widely distributed in foods, and high amounts are found in whole grain cereals, legumes, eggs, and meat. Pantothenic acid is needed to form coenzyme-A (CoA), and is critical in the metabolism and synthesis of carbohydrates, proteins, and fats. Adults require about 5 mg/day. Pantothenic acid is found in mushrooms, yeast, and liver.

Riboflavin (Vitamin B2)
Riboflavin (Vitamin B2) is involved in carbohydrate metabolism as an essential coenzyme in many oxidation-reduction reactions. Riboflavin is essentially nontoxic. Riboflavin deficiency usually occurs with other B-vitamin deficiencies. Symptoms and signs include sore throat, lesions of the lips and mucosa of the mouth, glossitis, conjunctivitis, seborrheic dermatitis, and normochromic-normocytic anemia. Riboflavin is found in mushrooms, yeast, and meats such as beef, pork, and lamb.

Thiamin (Vitamin B1)
Thiamin or Thiamine (vitamin B1) is widely available in the diet. Thiamin is involved in carbohydrate, fat, amino acid, glucose, and alcohol metabolism. Thiamin is essentially nontoxic. Thiamin deficiency (causing beriberi) is most common among people subsisting on highly refined rice or other carbohydrates in developing countries. Bean sprouts, brewer's yeast, and fortified cereals are good sources of thiamin.

Vitamin A
Vitamin A (retinol) is required for the formation of rhodopsin, a photoreceptor pigment in the retina. Vitamin A helps maintain epithelial tissues. Normally, the liver stores 90% of the body's Vitamin A. To use Vitamin A, the body releases it into the circulation bound to prealbumin (transthyretin) and retinol-binding protein. β-carotene and other provitamin carotenoids, contained in green leafy and yellow vegetables and deep- or bright-colored fruits, are converted to Vitamin A. Carotenoids are absorbed better from vegetables when they are cooked or homogenized and served with some fats or oils. The Recommended Dietary Allowance (RDA) of Vitamin A is 900 micrograms for men, and 700 micrograms for women. Deficiency impairs immunity and causes skin rashes and typical ocular effects such as dry eyes and night blindness.

Vitamin B12
Cobalamin is a general term for compounds with biologic vitamin B12 activity. These compounds are involved in nucleic acid metabolism, methyl transfer, and myelin synthesis and repair. They are necessary for the formation of normal red blood cells. Vitamin B12 is released in the stomach's acid environment and is bound to R protein. Pancreatic enzymes cleave the B12-R protein complex in the small intestine. After cleavage, intrinsic factor, secreted by parietal cells in the gastric mucosa, binds with vitamin B12. Intrinsic factor is required for absorption of vitamin B12, which takes place in the terminal ileum. The Recommended Dietary Allowance (RDA) is 2.4 micrograms, which is the amount found in 3 ounces (85 grams) of meat. Vitamin B12 is found in clams, oysters, turkey, chicken, beef, and pork. Dietary vitamin B12 deficiency usually results from inadequate absorption, but deficiency can develop in vegans who do not take vitamin supplements. Deficiency causes megaloblastic anemia, damage to the white matter of the spinal cord and brain, and peripheral neuropathy which is characterized by tingling or numbness in the hands or feet.

Vitamin B6
Vitamin B6 includes a group of closely related compounds: pyridoxine, pyridoxal, and pyridoxamine. They are metabolized in the body to pyridoxal phosphate, which acts as a coenzyme in many important reactions in blood, central nervous system, and skin metabolism. Vitamin B6 is important in the biosynthesis of heme and nucleic acid, as well as in lipid, carbohydrate, and amino acid metabolism. Vitamin B6 is found in a variety of vegetables and meats. Many breakfast cereals are fortified with Vitamin B6. Some natural sources of Vitamin B6 are brewer's yeast, Chinese cabbage (pak-choi), and red and green peppers.

Vitamin C
Vitamin C (ascorbic acid) plays a role in collagen, carnitine, hormone, and amino acid formation. It is essential for wound healing and facilitates recovery from burns. Vitamin C is also an antioxidant, supports immune function, and facilitates the absorption of iron. In developed countries, deficiency can occur with general undernutrition, but severe deficiency (causing scurvy) is uncommon. Symptoms of deficiency include fatigue, depression, and connective tissue defects such as gingivitis, rash, internal bleeding, or impaired wound healing. The Recommended Dietary Allowance (RDA) is 75 milligrams for women, 90 milligrams for men. The tolerable upper intake level of Vitamin C is approximately 2 grams (2000 mg) per day. Higher amounts can cause stomach upset and diarrhea. Vitamin C is found in fresh fruits and vegetables. Citrus fruits like oranges and lemons are good sources of vitamin C.

Vitamin D
Vitamin D has two main forms: D2 (ergocalciferol) and D3 (cholecalciferol). Vitamin D3 is synthesized in skin by exposure to sunlight (ultraviolet radiation) and obtained in the diet chiefly in fish liver oils and egg yolks. In some developed countries, milk and other foods are fortified with vitamin D. Human breast milk is low in vitamin D, containing an average of only 10% of the amount in fortified cow's milk. Requirements for vitamin D increase with aging. Vitamin D is a prohormone with several active metabolites that act as hormones. Vitamin D3 is metabolized by the liver to 25(OH)D, which is then converted by the kidneys to 1,25(OH)2D (1,25-dihydroxycholecalciferol, calcitriol, or active vitamin D hormone). 25(OH)D, the major circulating form, has some metabolic activity, but 1,25(OH)2D is the most metabolically active. Inadequate exposure to sunlight may cause vitamin D deficiency. Deficiency impairs bone mineralization, causing rickets in children and osteomalacia in adults and may contribute to osteoporosis.

The current recommendations from the Institute of Medicine are 200 IU/day from birth through age 50, 400 IU for those aged 51 to 70, and 600 IU for those over 70 years. These recommendations were established by determining the level of Vitamin D that was enough to prevent bone demineralization or rickets. The safe tolerable upper intake level for Vitamin D is 10,000 IU/day.

Randomized trials using the currently recommended intakes of 400 IU of Vitamin D/day have shown no appreciable reduction in fracture risk. In contrast, trials using 700-800 IU Vitamin D/day found less fracture incidence[8]. Adults should be consuming at least 1000 IU per day of Vitamin D to maintain blood serum levels that are effective for strengthening the bones.

Vitamin E
Vitamin E is a group of compounds (including tocopherols and tocotrienols) that have similar biologic activities. The most biologically active is α-tocopherol, but β-, γ-, and δ-tocopherols also have important biologic activity. These compounds act as antioxidants, which prevent lipid peroxidation of polyunsaturated fatty acids in cellular membranes. Plasma tocopherol levels vary with the total plasma lipid levels. Normally, the plasma α-tocopherol level is 5 to 20 μg/mL. Dietary vitamin E deficiency is common in developing countries. Vitamin E deficiency causes degeneration of the axons of neurons (nerve cells) resulting in neurologic deficits, and fragility of red blood cells which is generally diagnosed as hemolytic anemia. Taking Vitamin E supplements is not recommended because studies have found an increased risk of heart failure and general mortality. Vitamin E is found in spinach, watercress, mustard greens, and many green leafy vegetables. Good sources of Vitamin E are oily plant seeds such as peanuts and sunflower kernels.

Vitamin K
Vitamin K1 (phylloquinone) is dietary vitamin K. Dietary fat enhances its absorption. Infant formulas contain supplemental vitamin K. Vitamin K2 refers to a group of compounds (menaquinones) synthesized by bacteria in the intestinal tract; the amount synthesized does not satisfy the vitamin K requirement. The Recommended Dietary Allowance (RDA) is 120 micrograms for men, and 90 micrograms for women. Vitamin K controls the formation of coagulation factors II (prothrombin), VII, IX, and X in the liver. In healthy adults, dietary vitamin K deficiency is uncommon because vitamin K is widely distributed in green vegetables such as kale, spinach, and mustard greens. The bacteria of the normal gut also synthesize menaquinones.

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