Deficiency of vitamin

The Sugars Task Force s Select Committee on Nutrition and Human Needs recommended a daily consumption of sugars at 10% of total calories, which approximates current (11%) daily intake levels in the United States. At this level, sucrose does contribute to the development of dental caries however, no firm evidence exists that it causes dietary imbalances or deficiencies of vitamins (qv), minerals, or trace nutrients (62). 

Clinical manifestation of vitamin B 2 deficiency is usually a result of absence of the gastric absorptive (intrinsic) factor. Dietary deficiency of vitamin B 2 is uncommon and may take 20 to 30 years to develop, even in healthy adults who foUow a strict vegetarian regimen. An effective enterohepatic recycling of the vitamin plus small amounts from bacterial sources and other contaminants greatly minimizes the risk of a complete dietary deficiency. Individuals who have a defect in vitamin B 2 absorption, however, may develop a deficiency within three to seven years. 

Vitamin D [1406-12-2] is a material that is formed ia the skin of animals upon kradiation by sunlight and serves as a precursor for metaboUtes that control the animal s calcium homeostasis and act ki other hormonal functions. A deficiency of vitamin D can cause rickets, as weU as other disease states. This tendency can be a problem wherever animals, including humans, especially kifants and children, receive an kiadequate amount of sunshine. The latter phenomenon became prevalent with the advent of the kidustrial revolution, and efforts to cute rickets resulted ki the development of commercial sources of vitamin D for supplementation of the diet of Hvestock, pets, and humans. 

Nutritional deficiency of vitamin B12—Eat a balanced diet diat includes seafood, eggs, meals, and dairy products. 

The complex series of events in collagen maturation provide a model that illustrates the biologic consequences of incomplete polypeptide maturation. The best-known defect in collagen biosynthesis is scurvy, a result of a dietary deficiency of vitamin C required by... 

Peptidyl hydroxyprohne and hydroxylysine are formed by hydroxylation of peptidyl proline or lysine in reactions catalyzed by mixed-function oxidases that require vitamin C as cofactor. The nutritional disease scurvy reflects impaired hydroxylation due to a deficiency of vitamin C. 

Globally, undernutrition is widespread, leading to impaired growth, defective immune systems, and reduced work capacity. By contrast, in developed countries, there is often excessive food consumption (especially of fat), leading to obesity and to the development of cardiovascular disease and some forms of cancer. Deficiencies of vitamin A, iron, and iodine pose major health concerns in many countries, and deficiencies of other vitamins and minerals are a major cause of iU health. In developed countries, nutrient deficiency is rare, though there are vulnerable sections of the population at risk. Intakes of minerals and vitamins that are adequate to prevent deficiency may be inadequate to promote optimum health and longevity. 

In experimental animals, vitamin E deficiency results in resorption of femses and testicular atrophy. Dietary deficiency of vitamin E in humans is unknown, though patients with severe fat malabsorption, cystic fibrosis, and some forms of chronic fiver disease suffer deficiency because they are unable to absorb the vitamin or transport it, exhibiting nerve and muscle membrane damage. Premamre infants are born with inadequate reserves of the vitamin. Their erythrocyte membranes are abnormally fragile as a result of peroxidation, which leads to hemolytic anemia. 

When acting as a methyl donor, 5-adenosylmethionine forms homocysteine, which may be remethylated by methyltetrahydrofolate catalyzed by methionine synthase, a vitamin Bj2-dependent enzyme (Figure 45-14). The reduction of methylene-tetrahydrofolate to methyltetrahydrofolate is irreversible, and since the major source of tetrahydrofolate for tissues is methyl-tetrahydrofolate, the role of methionine synthase is vital and provides a link between the functions of folate and vitamin B,2. Impairment of methionine synthase in Bj2 deficiency results in the accumulation of methyl-tetrahydrofolate—the folate trap. There is therefore functional deficiency of folate secondary to the deficiency of vitamin B,2. 

Deficiency of fohc acid itself—or deficiency of vitamin Bi2, which leads to functional fohc acid deficiency—affects cells that are dividing rapidly because they have a large requirement for thymidine for DNA synthesis. ChnicaUy, this affects the bone marrow, leading to megaloblastic anemia. 

Megaloblastic anemias Deficiency of vitamin 6,2 Decreased absorption of 6,2, often due to a deficiency of intrinsic factor, normally secreted by gastric parietal cells... 

Neuropathy can result from deficiency of vitamins or hormones. Alcoholics often obtain a large proportion of their caloric needs from ethanol, and hence become thiamine-deficient. Alcoholic neuropathy results from a combination of thiamine deficiency, which impairs... 

Morphologic classifications are based on cell size. Macrocytic cells are larger than normal and are associated with deficiencies of vitamin B12 or folate. Microcytic cells are smaller than normal and are associated with iron deficiency whereas normocytic anemia may be associated with recent blood loss or chronic disease. 

G12. Girdwood, R. H., Microbiological methods of assay in clinical medicine with particular reference to the investigation of deficiency of vitamin B12 and folic acid. Scot. Med. J. 5, 10-22 (1960). 

Deficiency of vitamin D in childhood produces rickets, a constellation of skeletal abnormalities most strikingly seen as deformities of the legs, but many other developing bones are affected. Muscle weakness is common. 

Cobalt occurs in vitamin B12. This vitamin is very complex and is required for some exotic reactions of metabolism. A deficiency of vitamin B12 results in pernicious anemia. More about this vitamin follows in chapter 15. 

Depending on age, adult men require 1.3-1.7 mg/day and adult women 1.3-1.5 mg/day. Women who are pregnant or lactating require 1.9-2.0 mg/day. Deficiency of vitamin Be in the developed world is rare as many foods are good... 

Among the aged, deficiency of vitamin B12 is rather common. Upon aging, many people become unable to absorb adequate amounts of vitamin B12 from the diet. Functional deficits are the result. These are easily overcome by the monthly injection of vitamin B12 supplements. 

Xerophthaimia night blindness, occasioned by a deficiency of vitamin A. 

Deficiency of vitamin B12 interferes with production of red blood cells so that anaemia (megaloblastic anaemia) develops (Chapter 15). 

The importance of this reaction is suggested from the observation that, if the level of the methylating agent is low (which can be caused by deficiency of vitamin B12 and/or folic acid), this can restrict formation of phosphatidyl... 

Retinoids play a role in the regulation of differentiation and development. This they achieve by binding to retinoid receptor-proteins in the nucleus and inhibiting the expression of transcription factors that regulate proliferation. Hence, deficiency of vitamin A can result in impaired differentiation and hence foetal malformation and spon-... 

A deficiency of vitamin A results in night blindness. A chronic deficiency results in a thickening of membranes in the cornea which, if untreated, can lead to blindness through perforation of the cornea and loss of the lens. It is estimated that half a million children develop blindness due to vitamin A deficiency every year. Refeeding malnourished children can produce a deficiency of vitamin A (see below). 

Deficiency of vitamin E is rare it can occur from abnormalities in lipid absorption as well as dietary deficiency. Its deficiency affects the muscular system, causing dystrophy and paralysis and, if the heart is affected, death by myocardial failure. This is probably caused by demyelin-ation of axons due to oxidative damage. Vitamin E is incorporated into chylomicrons within the enterocyte, so that its uptake into cells requires the activity of lipoprotein lipase. 

Less activity in the open air and poor nutrition can result in a deficiency of vitamin D and be responsible, in part, for osteoporosis. 

The clinical problems that arise in the menopause are hot flushes, sweating, depression, decreased libido, increased risk of cardiovascular disease and osteoporosis. The latter results in increased incidence of hip, radial and vertebral fractures. Oestrogen is one factor controlling synthesis of active vitamin D and osteoporosis is in part due to a deficiency of vitamin D. Not surprisingly, to reduce these problems, administration of oestrogen is recommended (known as hormone replacement therapy or HRT). HRT reduces some of the risk factors for coronary artery disease since it reduces blood pressure and decreases the blood level of LDL-cholesterol and increases that of HDL-cholesterol. However, there is considerable debate about whether HRT increases the risk of breast or endometrial cancer. 

A deficiency of vitamin A leads to vision defects, including a visual impairment at low light levels, termed night blindness. For the processes of vision, retinol needs to be converted first by oxidation into the aldehyde retinal, and then by enzymic isomerization to cw-retinal. c -Retinal is then bound to the protein opsin in the retina via an imine linkage (see Section 7.7.1) to give the red visual pigment rhodopsin. 

Cell multiplication is inhibited because DNA synthesis is insufficient. This occurs in deficiencies of vitamin Bu or folic acid (macrocytic hyperchromic anemia). 2. Hemoglobin synthesis is impaired. This situation arises in iron deficiency, since Fe + is a constituent of hemoglobin (microcytic hypochromic anemia). 

Dietary deficiency of vitamin ieads to impaired amino acid metabolism in many organs, but the CNS is most severeiy affected. 

Deficiency of vitamin K, which Is fat-soluble, is rare and produces only mild symptoms such as a delay in blood clotting (prolongedprothrombin time) In adults. 

Osteomalacia is the condition in which bone becomes demineralised due to deficiency of vitamin D. In this condition parathyroid hormone (PTH) acts on the bone to maintain serum calcium, resulting in demineralisation. Serum calcium is usually normal or slightly low alkaline phosphatase levels are high, reflecting excessive osteoblast activity, and serum phosphate falls as an effect of PTH on the kidney. The same condition in children results in defects in long bone formation, and is termed rickets. 

Deficiency of vitamin E is characterized by low serum tocopherol levels and a positive hydrogen peroxide hemolysis test. This deficiency is believed to occur in patients with biliary, pancreatic, or intestinal disease that is characterized by excessive steatorrhea. Premature infants with a high intake of fatty acids exhibit a deficiency syndrome characterized by edema, anemia, and low tocopherol levels. This condition is reversed by giving vitamin E. 

The deficiency of vitamin K occur due to liver disease, jaundice, malabsorption syndromes and chronic use of antimicrobial agents. 

Therapeutically, vitamin K is used in prophylaxis and treatment of deficiency of clotting factor due to dietary deficiency of vitamin K, chronic antimicrobial therapy, malabsorption syndrome, obstructive jaundice, liver diseases such as cirrhosis and hepatitis, in neonates to prevent or treat haemorrhagic disease of new born to counteract the overdosing of oral anticoagulants... 

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