Conditions Associated with
Sources and RDA* for Adults
Conditions Associated with
Thiamine Destroyed by heat and (Vitamin oxygen, especially in Bi) alkaline environment
Riboflavin Stable to heat, acids, (Vitamin and oxidation; B2) destroyed by bases and ultraviolet light
Niacin Stable to heat, acids,
(Nicotinic and bases; converted acid) to niacinamide by cells; synthesized from tryptophan
Pantothenic Destroyed by heat, acid acids, and bases
Vitamin Be Group of three compounds; stable to heat and acids; destroyed by oxidation, bases, and ultraviolet light
Cyanoco- Complex, cobalt-
balamin containing compound; (Vitamin stable to heat; B12) inactivated by light, strong acids, and strong bases; absorption regulated by intrinsic factor from gastric glands; stored in liver
Folacin Occurs in several forms;
(Folic destroyed by oxidation acid) in acid environment or by heat in alkaline environment; stored in liver where it is converted into folinic acid
Biotin Stable to heat, acids, and light; destroyed by oxidation and bases
Ascorbic Chemically similar to acid monosaccharides;
(Vitamin stable in acids but C) destroyed by oxidation, heat, light, and bases
Part of coenzyme needed for oxidation of carbohydrates; coenzyme needed in synthesis of ribose Part of enzymes and coenzymes, such as FAD, needed for oxidation of glucose and fatty acids and for cellular growth Part of coenzymes NAD and NADP needed for oxidation of glucose and synthesis of proteins, fats, and nucleic acids Part of coenzyme A needed for oxidation of carbohydrates and fats Coenzyme needed for synthesis of proteins and various amino acids, for conversion of tryptophan to niacin, for production of antibodies, and for synthesis of nucleic acids
Lean meats, liver, eggs, whole-grain cereals, leafy green vegetables, legumes 1.5 mg
Meats, dairy products, leafy green vegetables, whole-grain cereals 1.7 mg
Liver, lean meats, peanuts, legumes 20 mg
Meats, whole-grain cereals, legumes, milk, fruits, vegetables 10 mg
Liver, meats, bananas, avocados, beans, peanuts, whole-grain cereals, egg yolk 2 mg
Excesses None known
Part of coenzyme needed for synthesis of nucleic acids and for metabolism of carbohydrates; plays role in synthesis of myelin; needed for normal red blood cell production
Liver, meats, milk, cheese, eggs 3-6 |ig
Coenzyme needed for metabolism of certain amino acids and for synthesis of DNA; promotes production of normal red blood cells
Coenzyme needed for metabolism of amino acids and fatty acids and for synthesis of nucleic acids
Needed for production of collagen, conversion of folacin to folinic acid, and metabolism of certain amino acids; promotes absorption of iron and synthesis of hormones from cholesterol
Liver, leafy green vegetables, whole-grain cereals, legumes 0.4 mg
Liver, egg yolk, nuts, legumes, mushrooms 0.3 mg
Citrus fruits, tomatoes, potatoes, leafy green vegetables 60 mg
Beriberi, muscular weakness, heart enlarges
Dermatitis, blurred vision
Pellagra, photosensitive dermatitis, diarrhea, mental disorders Rare, loss of appetite, mental depression, muscle spasms Rare, convulsions, vomiting, seborrhea lesions
Exacerbates gout and kidney stone formation
Rare, elevated blood cholesterol, nausea, fatigue, anorexia Scurvy, lowered resistance to infection, wounds heal slowly
*RDA = recommended dietary allowance.
may vary. However, a daily intake of 800 mg is sufficient to cover adult requirements in spite of variations in absorption.
Only a few foods contain significant amounts of calcium. Milk and milk products and fish with bones, such as salmon or sardines, are the richest sources. Leafy green vegetables, such as mustard greens, turnip greens, and kale, are good sources, but because one must consume large amounts of these vegetables to obtain sufficient minerals, most people must regularly consume milk or milk products to maintain an adequate intake of calcium.
Calcium deficiency in children causes stunted growth, misshapen bones, and enlarged wrists and ankles. In adults, such a deficiency may remove calcium from the bones, thinning them and raising risk of fracture. Because calcium is required for normal closing of the sodium channels in nerve cell membranes, too little calcium (hypocalcemia) can cause tetany. Extra calcium demands in pregnancy can cause cramps.
A study of more than 4,000 children and adolescents aged 2 to 17 years found that excessive drinking of carbonated beverages is associated with eating less vitamin A, calcium, and magnesium. Drinking tea and coffee had no effect on nutrient consumption.
2. Phosphorus. Phosphorus (P) is responsible for about 1% of total body weight, and most of it is incorporated in the calcium phosphate of bones and teeth. The remainder serves as structural components and plays important roles in nearly all metabolic reactions. Phosphorus is a constituent of nucleic acids, many proteins, some enzymes, and some vitamins. It is also found in the phospholipids of cell membranes, in the energy-carrying molecule ATP, and in the phosphates of body fluids that regulate pH. (Review the molecular structure of ATP in fig. 4.7.)
The recommended daily adult intake of phosphorus is 800 mg, and since this mineral is abundant in protein foods, diets adequate in proteins are also adequate in phosphorus. Phosphorus-rich foods include meats, cheese, nuts, whole-grain cereals, milk, and legumes.
D What are the functions of calcium?
9 What are the functions of phosphorus?
9 Which foods are good sources of calcium and phosphorus?
3. Potassium. Potassium (K) is widely distributed throughout the body and is concentrated inside cells rather than in extracellular fluids. On the other hand, sodium, which has similar chemical properties, is concentrated outside cells. The ratio of potassium to sodium within a cell is 10:1, whereas the ratio outside the cell is 1:28.
Potassium helps maintain intracellular osmotic pressure and pH. It promotes reactions of carbohydrate and protein metabolism and plays a vital role in establishing the membrane potential that occurs in nerve impulse conduction and muscle fiber contraction.
Nutritionists recommend a daily adult intake of 2.5 grams (2,500 mg) of potassium. Because this mineral is widely distributed in foods, a typical adult diet provides between 2 and 6 grams each day. Dietary potassium deficiency is rare, but it may occur for other reasons. For example, when a person has diarrhea, the intestinal contents may pass through the digestive tract so rapidly that potassium absorption is greatly reduced. Vomiting or using diuretic drugs may also deplete potassium. The consequences of such losses may include muscular weakness, cardiac abnormalities, and edema.
Foods rich in potassium are avocados, dried apricots, meats, milk, peanut butter, potatoes, and bananas. Citrus fruits, apples, carrots, and tomatoes provide lesser amounts.
U How is potassium distributed in the body?
9 What is the function of potassium?
9 Which foods are good sources of potassium?
4. Sulfur. Sulfur (S) is responsible for about 0.25% of body weight and is widely distributed through tissues. It is particularly abundant in skin, hair, and nails. Most sulfur is part of the amino acids methionine and cysteine. Other sulfur-containing compounds include thiamine, insulin, and biotin (fig. 18.16). In addition, sulfur is a constituent of mucopolysaccharides found in cartilage, tendons, and bones and of sulfolipids that are in the liver, kidneys, salivary glands, and brain.
No daily requirement for sulfur has been established. It is thought, however, that a diet providing adequate amounts of protein will also meet the body's need for sulfur. Good food sources of this mineral include meats, milk, eggs, and legumes.
5. Sodium. About 0.15% of adult body weight is due to sodium (Na), which is widely distributed throughout the body. Only about 10% of this mineral is inside the cells, and about 40% is within the extracellular fluids. The remainder is bound to the inorganic salts of bones.
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