Water-soluble vitamins include B complex and C. These vitamins dissolve in water and are easily destroyed by air, light, and cooking. They are not stored in the body to the extent that fat-soluble vitamins are stored.
Beriberi is a disease that affects the nervous, cardiovascular, and gastroin-testinal systems. The legs feel heavy, the feet burn, and the muscles degener-ate. The patient is irritable and suffers from headaches, depression, anorexia, constipation, tachycardia (rapid heart rate), edema, and heart failure.
Toward the end of the nineteenth century, a doctor in Indonesia discovered that chickens that were fed table scraps of polished rice developed symptoms much like those of his patients suffering from beriberi. When these same chickens were later fed brown (unpolished) rice, they recovered.
Some years later, this mysterious component of unpolished rice was rec-ognized as an essential food substance and was named vitamin B. Subsequently, it was named vitamin B complex because the vitamin was found to be composed of several compounds. The B-complex vitamins are listed in Table 7-1.
Thiamine, a coenzyme, was originally named vitamin B1. It is partially de-stroyed by heat and alkalies, and it is lost in cooking water.
Functions.Thiamine is essential for the metabolism of carbohydrates andsome amino acids. It is also essential to nerve and muscle action. It is absorbed in the small intestine.
Sources.Thiamine is found in many foods, but generally in small quantities.(See Appendix D.) Some of the best natural food sources of thiamine are unrefined and enriched cereals, whole grains, lean pork, liver, seeds, nuts, and legumes.
Requirements.Thiamine is measured in milligrams. The daily thia-mine requirement for the average adult female is 1.1 mg a day, and for the average adult male it is 1.2 mg a day. The requirement is not thought to increase with age. In general, however, an increase in calories increases the need for thiamine.
Most breads and cereals in the United States are enriched with thiamine, so that the majority of people can and do easily fulfill their recommended intake.
Deficiency.Symptoms of thiamine deficiency include loss of appetite,fatigue, nervous irritability, and constipation. An extreme deficiency causes beriberi. Its deficiency is rare, however, occurring mainly among alcoholics whose diets include reduced amounts of thiamine while their requirements are increased and their absorption is decreased. Others at risk include renal clients undergoing long-term dialysis, clients undergoing bypass surgery for weight loss, and those who eat primarily rice.
Because some raw fish contain thiaminase, an enzyme that inhibits the normal action of thiamine, frequent consumption of large amounts of raw fish could cause thiamine deficiency. Eating raw fish is not recommended. Cooking inactivates this enzyme.
There are no known ill effects from excessive oral intake of thiamine, but it may be toxic if excessive amounts are given intravenously.
Riboflavin is sometimes called B2. It is destroyed by light and irradiation andis unstable in alkalies.
Functions.Riboflavin is essential for carbohydrate, fat, and protein me-tabolism. It is also necessary for tissue maintenance, especially the skin around the mouth, and for healthy eyes. Riboflavin is absorbed in the small intestine.
Sources.Riboflavin is widely distributed in animal and plant foods but insmall amounts. Milk, meats, poultry, fish, and enriched breads and cereals are some of its richest sources. Some green vegetables such as broccoli, spinach, and asparagus are also good sources.
Requirement.Riboflavin is measured in milligrams. The average adultfemale daily requirement is thought to be 1.1 mg, and the adult male require-ment is 1.3 mg. The riboflavin requirement appears to increase with increased energy expenditure. The requirement does not diminish with age.
Deficiency.Because of the small quantities of riboflavin in foods and itslimited storage in the body, deficiencies of riboflavin can develop. The generous use of fat-free milk in the diet is a good way to prevent deficiency of this vitamin. It is important, however, that milk be stored in opaque containers because riboflavin can be destroyed by light. It appears that fiber laxatives can reduce riboflavin absorption, and their use over long periods should be discouraged.
A deficiency of riboflavin can result in cheilosis, a condition characterized by sores on the lips and cracks at the corners of the mouth (Figure 7-1), glossitis (inflammation of the tongue), dermatitis, and eye strain in the form of itching, burning, and eye fatigue. Its toxicity is unknown.
Niacin is the generic name for nicotinic acid and nicotinamide. Niacin is fairlystable in foods. It can withstand reasonable amounts of heat and acid and is not destroyed during food storage.
Functions.Niacin serves as a coenzyme in energy metabolism and con-sequently is essential to every body cell. In addition, niacin is essential for the prevention of pellagra. Pellagra is a disease characterized by sores on the skin and by diarrhea, anxiety, confusion, irritability, poor memory, dizziness, and untimely death if left untreated. Niacin, when used as a cholesterol-lowering agent, must be closely supervised by a physician because of possible adverse side effects such as liver damage and peptic ulcers.
Sources.The best sources of niacin are meats, poultry, and fish. Peanuts andother legumes are also good sources. Enriched breads and cereals also contain some. Milk and eggs do not provide niacin per se, but they are good sources of its precursor, tryptophan (an amino acid). Vegetables and fruits contain little niacin.
Requirements.Niacin is measured in as aniacin equivalent (NE).OneNE equals 1 mg of niacin or 60 mg of tryptophan. The general recommenda-tion is a daily intake of 14 mg/NE for adult women and 16 mg/NE for adult men. Because excessive amounts of niacin have caused flushing due to vascular dilation (expansion of blood vessels), self-prescribed doses of niacin concentrate should be discouraged. Other symptoms include gastrointestinal problems and itching. If excessive amounts of niacin are ingested, liver damage may result.
Deficiency.A deficiency of niacin is apt to appear if there is a deficiency ofriboflavin. Symptoms of niacin deficiency include weakness, anorexia, indiges-tion, anxiety, and irritability. In extreme cases, pellagra may occur.
Vitamin B6 is composed of three related forms: pyridoxine, pyridoxal, and pyri-doxamine. It is stable to heat but sensitive to light and alkalies.
Functions.Vitamin B6is essential for protein metabolism and absorption,and it aids in the release of glucose from glycogen. With the help of vitamin B6, amino acids present in excessive amounts can be converted to those in which the body is temporarily deficient. It also serves as a catalyst in the conversion of tryptophan to niacin, and it is helpful in the formation of other substances from amino acids. An example is the synthesis of neurotransmitters such as serotonin and dopamine.
Sources.Some of the nutrient-dense sources of vitamin B6are poultry,fish, liver, kidney, potatoes, bananas, and spinach. Whole grains, especiallyoats and wheat, are good sources of vitamin B6, but because this vitamin is lost during milling and is not replaced during the enrichment process, refined grains are not a good source.
Requirements.Vitamin B6is measured in milligrams, and the need in-creases as the protein intake increases. For adult females, the daily requirement is 1.3 to 1.5 mg and for males, 1.3 to 1.7 mg. Oral contraceptives interfere with the metabolism of vitamin B6 and can result in a deficiency.
Deficiency. A deficiency of vitamin B6is usually found in combination withdeficiencies of other B vitamins. Symptoms include irritability, depression, and dermatitis. In infants, its deficiency can cause various neurological symptoms and abdominal problems. Although its toxicity is rare, it can cause temporary neurological problems.
Vitamin B12(cobalamin) is a compound that contains the mineral cobalt. It is slightly soluble in water and fairly stable to heat, but it is damaged by strong acids or alkalies and by light. It can be stored in the human body for 3 to 5 years.
Functions.Vitamin B12is involved in folate metabolism, maintenance ofthe myelin sheath, and healthy red blood cells. In order for vitamin B12 to be absorbed, it must bind with a glycoprotein (intrinsic factor) present in gastric secretions in the stomach and travel to the small intestine, where it combines with pancreatic proteases, then travels to the ileum, where it attaches to special recep-tor cells to complete the absorption process. A patient who has lost the ability to produce the gastric secretions, pancreatic proteases, intrinsic factor, or the special receptor cells because of disease or surgery will develop pernicious anemia.
Sources.The best food sources of B12are animal foods, especially organmeats, lean meat, seafood, eggs, and dairy products.
Requirements.Vitamin B12is measured in micrograms. The DRI foradults is 2 to 4μg a day, but it increases during pregnancy and lactation. The amount absorbed will depend on current needs.
Deficiency.Fortunately, a vitamin B12deficiency is rare and is thought tobe caused by congenital problems of absorption, which inhibit the body’s abil-ity to absorb or synthesize sufficient amounts of vitamin B12. It may also be due to years of a strict vegetarian diet that contains no animal foods.
When the amount of B12 is insufficient, megaloblastic anemia may result. If the intrinsic factor is missing, pernicious anemia develops. Intrinsic factor could be missing because of surgical removal of the stomach, or a large portion of it, or because of disease or surgery affecting the ileum. Dietary treatment will be ineffective; the patient must be given intramuscular injections of B12, usu-ally on a monthly basis.
Vitamin B12 deficiency may also result in inadequate myelin synthesis. This deficiency causes damage to the nervous system. Signs of vitamin B12 defi-ciency include anorexia, glossitis, sore mouth and tongue, pallor, neurological upsets such as depression and dizziness, and weight loss.
Folate, folacin, and folic acid are chemically similar compounds. Their namesare often used interchangeably.
Functions.Folate is needed for DNA synthesis, protein metabolism, andthe formation of hemoglobin. Researchers have concluded that folic acid helps to prevent colon, cervical, esophageal, stomach, and pancreatic cancers. Folic acid also increases homocystein levels that help prevent strokes, blood vessel disease, macular degeneration, and Alzheimer’s disease.
Sources.Folate is found in many foods, but the best sources are cerealsfortified with folate, green leafy vegetables, legumes, sunflower seeds, and fruits such as orange juice and strawberries. Heat, oxidation, and ultraviolet light all destroy folate, and it is estimated that 50% to 90% of folate may be destroyed during food processing and preparation. Consequently, it is advisable that fruits and vegetables be eaten uncooked or lightly cooked whenever possible.
Requirements.Folate is measured in micrograms. The average dailyrequirement for the adult female is 400 g, and for the adult male it is also 400μg. There is an increased need for folate during pregnancy and periods of growth because of the increased rate of cell division and the DNA synthe-sis in the body of the mother and of the fetus. Consequently, it is extremely important that women of childbearing age maintain good folate intake. The recommended amount for a woman 1 month before conception and through the first 6 weeks of pregnancy is 600μg a day.
Deficiency.Folate deficiency has been linked toneural tube defects(NTDs) in the fetus, such as spina bifida (spinal cord or spinal fluid bulgethrough the back) and anencephaly (absence of a brain). Other signs of deficiency are inflammation of the mouth and tongue, poor growth, depression and mental confusion, problems with nerve functions, and megaloblasticanemia. Megaloblastic anemia is a condition wherein red blood cells are largeand immature and cannot carry oxygen properly.
Hypervitaminosis.The FDA limits the amount of folate in over-the-counter(OTC) supplements to 100μg for infants, 300μg for children, and 400μg for adults because consuming excessive amounts of folate can mask a vitamin B12 deficiency and inactivate phenytoin, an anticonvulsant drug used by epileptics.
Function and Sources. Biotinparticipates as a coenzyme in the syn-thesis of fatty acids and amino acids. Some of its best dietary sources are egg yolks, milk, poultry, fish, broccoli, spinach, and cauliflower. Biotin is also synthesized in the intestine by microorganisms, but the amount that is available for absorption is unknown.
Requirements.Biotin is measured in micrograms. The Food and Nutri-tion Board of the Institute of Medicine has established an AI of 30μg for adults (see Table 7-2).
Deficiency.Deficiency symptoms include nausea, anorexia, depression,pallor (paleness of complexion), dermatitis (inflammation of skin), and an in-crease in serum cholesterol. Toxicity from excessive intake is unknown.
Pantothenic acid is appropriately named because the Greek wordpantothenmeans “from many places.” It is fairly stable, but it can be damaged by acids and alkalies.
Functions.Pantothenic acid is involved in metabolism of carbohydrates,fats, and proteins. It is also essential for the synthesis of the neurotransmitter acetylcholine and of steroid hormones.
Sources.Pantothenic acid is found extensively in foods, especially animalfoods such as meats, poultry, fish, and eggs. It is also found in whole-grain cere-als and legumes. In addition, it is thought to be synthesized by the body.
Requirements.There is no DRI for pantothenic acid, but the Food andNutrition Board has provided an estimated intake of 4 to 7 mg a day for normal adults (see Table 7-2).
Deficiency.Natural deficiencies are unknown. However, deficiencies havebeen produced experimentally. Signs include weakness, fatigue, and a burning sensation in the feet. Toxicity from excessive intake has not been confirmed.
Vitamin C is also known as ascorbic acid. It has antioxidant properties and protects foods from oxidation, and it is required for all cell metabolism. It is read-ily destroyed by heat, air, and alkalies, and it is easily lost in cooking water.
Functions.Vitamin C is known to preventscurvy.This is a disease char-acterized by gingivitis (soft, bleeding gums and loose teeth); flesh that is easily bruised; tiny, pinpoint hemorrhages of the skin; poor wound healing; sore joints and muscles; and weight loss. In extreme cases, scurvy can result in death. Scurvy used to be common among sailors, who lived for months on bread, fish, and salted meat, with no fresh fruits or vegetables. During the middle of the eighteenth century, it was discovered that the addition of limes or lemons to their diets prevented this disease.
Vitamin C also has an important role in the formation of collagen, a pro-tein substance that holds body cells together, making it necessary for wound healing. Therefore, the requirement for vitamin C is increased during trauma, fever, and periods of growth. Tiny, pinpoint hemorrhages are symptoms of the breakdown of collagen.
Vitamin C aids in the absorption of nonheme iron (from plant and ani-mal sources and less easily absorbed than heme iron) in the small intestine when both nutrients are ingested at the same time. Because of this, it is called an iron enhancer.
Vitamin C also appears to have several other functions in the human body that are not well understood. For example, it may be involved with the forma-tion or functioning of norepinephrine (a neurotransmitter and vasoconstrictor that helps the body cope with stressful conditions), some amino acids, folate, leukocytes (white blood cells), the immune system, and allergic reactions.
It is believed to reduce the severity of colds because it is a natural antihista-mine, and it can reduce cancer risk in some cases by reducing nitrites in foods.
Vitamin C is absorbed in the small intestine.
Sources.The best sources of vitamin C are citrus fruits, melon, strawber-ries, tomatoes, potatoes, red and green peppers, cabbage, and broccoli.
Requirements.Vitamin C is measured in milligrams. Under normal cir-cumstances, an average female adult in the United States requires 75 mg a day and an average male 90 mg. In times of stress, the need is increased. Regular cigarette smokers are advised to ingest 125 mg or more a day.
It is generally considered nontoxic, but this has not been confirmed. An excess can cause diarrhea, nausea, cramps, an excessive absorption of food iron, rebound scurvy (when megadoses are stopped abruptly), and possibly oxalate kidney stones.
Deficiency.Deficiencies of vitamin C are indicated by bleeding gums, looseteeth, tendency to bruise easily, poor wound healing, and, ultimately, scurvy.