Vitamin intestinal synthesis

Only microorganisms are able to synthesize vitamin B12. Microbiological vitamin B12 synthesis in humans takes place, however, in the lower intestine where the... 

Factors which cause a decrease in bioavailability include 111 high urinary excretion (2) destruction by certain mlesiinal bacteria (2) increased urinary excretion caused by vitamin C (4) presence of sulfonamides which block intestinal synthesis and (5) a decrease in absorption mechanisms. Increase in bioavailability can be provided by stimulating intestinal bacterial synthesis in certain species. No toxicity due to folic acid has been reported in humans. 

Bioavailability of Niacin. Factors which cause a decrease in macm availability include (1) Cooking losses (2) bound form in corn (maize), greens, and seeds is only partially available (3) presence of oral antibiotics (4) diseases which may cause decreased absorption (5) decrease in tiyptophan conveision as in a vitamin B deficiency. Fac.tois that increase availability include (1) alkali treatment of cereals (2) storage in bver and possibly in muscle and kidney tissue and (3) increased intestinal synthesis. 

The recommended dietary allowance (RDA) for vitamin D is 5 fig (200 IU)/d, but this value includes casual exposure to sunlight without regard to lifestyle or climate. For individuals who do not receive adequate sunlight because of illness, advanced age, or are otherwise shut in, the actual daily requirement for vitamin D3 could be as much as 15 fig/d. Vitamin D3 deficiency also may occur with chronic biliary obstruction and steatorrhoea limiting intestinal absorption of vitamin D3 and lead to osteomalacia [44], Another factor is the increased use of sunscreens among Western societies, that limits the penetration of UV photons to the site of vitamin D3 synthesis [41,45,46],... 

Q4 The water-soluble vitamins (B and C) and essential minerals, such as iron, are absorbed in the small intestine. The reabsorption of iron in the duodenum and proximal jejunum involves a complex active transport process. When there is a large reduction in the surface area of this part of the gut, there is a marked reduction in reabsorption of iron (and B vitamins). Haemoglobin synthesis is decreased, leading to development of anaemia, which is a common symptom in celiac disease. 

Altered gut vitamin K synthesis. Vitamin K antagonizes the effects of warfarin. External sources of vitamin K include the diet and intestinal flora, the latter only becoming significant in those with a low dietary intake of the vitamin. Broad-spectrum antibiotics that may reduce intestinal bacteria may alter the effect of warfarin. 

PTH also acts to increase absorption of calcium ion by the small intestine. It does this indirectly by promoting the formation of active vitamin D in the kidney. PTH acts on the final, rate-limiting step in vitamin D synthesis, the formation of 1,25-dihydroxycholecalciferol in the kidney. If PTH is low, formation of the inactive derivative, 24,25-dihydroxycholecalciferol, is stimulated instead. Vitamin D acts on intracellular receptors in the small intestine to increase transcription of genes encoding calcium uptake systems, to up-regulate their expression. 

Inhibitory effect on intestinal vitamin K synthesis, VI, 41 7,12-DiketochoIanic acid, configuration, VIII, 261 Dimenformon, see Estradiol benzoate 2,3-Dimercaptopropanol (BAL), as antidote against lewisite, VII, 106 mercury, VII, 106 mustard gas, VII, 106... 

Increased absorption is almost certainly the cause of the raising of the blood and tissue levels of vitamin B12 by sorbitol and some other substances. Intestinal synthesis is responsible for the far more dramatic sparing of other B vitamins by sorbitol, ascorbic acid, and several other substances, so that animals become completely independent of dietary sources of these vitamins. Finally, the ability of ascorbic acid to prolong the life of animals deficient in folic acid is very probably due to the promotion of the synthesis of this vitamin in the tissues. 

These studies show that germ-free existence is possible. In addition they throw fresh light on the question of intestinal synthesis of B vitamins, for the concentration of B vitamins in the gut does not necessarily imply bacterial synthesis. 

Since naturally occurring forms of vitamin K are fat-soluble, absorption is related to that of fat and is impaired when bile is absent from the intestinal tract and in the steatorrheas. It is conceivable that prolonged administration of antibiotics may depress intestinal synthesis of vitamin K and lead to deficiency. The deficiency which occurs in newborn infants may be due largely to limited food intake or, perhaps, to sterility of the intestinal tract. 

Another of the water-soluble B vitamins known to have a function for some bacteria and animals is biotin. A role in carbohydrate metabolism has been suggested. A protein substance called avidin, when fed in the form of large amounts of raw egg yolk, combines with biotin, and may thus cause a biotin deficiency in some species. Somewhat similar symptoms have been reported in human subjects (Sydenstricker et al., 1942). Intestinal synthesis and the antivitamin may explain the failure to confirm this observation. No definite requirement for the diet can be stated. 

Vitamin K is required for proper blood clotting. The letter K conies from koagulation, which is German for clotting. Vitamin K is found in the leaves of green plants. Deficiencies are rare because the vitamin is also synthesized by intestinal bacteria. Vitamin KH2 (the hydroquinone of vitamin K) is the coenzyme form of the vitamin. The synthesis of vitamin KH2 is desaibed in Section 19.8. 

C. Some products include 9ullaquinoxaUne> which enharxies toxicity by inhibiting vitamin K synthesis in the intestine and colon. 

In addition to having activity as a growth factor for certain bacteria, PABA has considerable folacin activity when fed to deficient animals in which intestinal synthesis of folacin takes place. For example, for rats and mice, it can completely replace the need for a dietary source of folacin. This explains why para-aminobenzoic acid was once considered to be a vitamin in its own right. 

Intestinal synthesis. Vitamin K, is synthesized by the normal bacteria in the small intestine and the colon hence, an adequate supply is generally present. Since the intestine of a newborn infant is sterile at birth, however, the supply of vitamin K is inadequate until normal bacterial flora of the intestine develops on about the third or fourth day of life. 

The intestinal synthesis of vitamin K reduces the food dietary requirements for the vitamin in man and other mammals (but not birds birds have such a short intestinal tract and harbor so few microorganisms that they require a dietary source of vitamin K), although it appears that little of the vitamin K produced in the lower gut is absorbed. It is noteworthy, however, that animals that practice coprophagy, such as the rabbit, can utilize much of the vitamin K that is eliminated in the feces. 

RECOMMENDED DAILY ALLOWANCE OF VITAMIN K. Because of the synthesis of vitamin K by intestinal bacteria in healthy individuals (except newborn babies), no specific recommended allowance is made for this vitamin by the Food and Nutrition Board of the NRC-National Academy of Sciences. However, because the adequacy of the intestinal synthesis over a long period is uncertain, NRC does give an estimated adequate dietary intake of vitamin K. (See section on VITAMIN [S], Tab le V-5, Vitam i n Tab le.)... 

Roth et al. (196), using C -carboxyl labeled nicotinic acid or nicotinamide, have shown that the compounds are rapidly excreted. A total of about 3% of the carboxyl group was expired as carbon dioxide within 1 day after the injection. A few more per cent is given off as exhaled carbon dioxide several days later. It has been estimated that approximately 15 % of the radioactivity fixed in the tissue is exhaled as carbon dioxide. In later studies it was shown that carbon dioxide production from labeled nicotinic acid and nicotinamide also occurs in hamsters, rats, and dogs (221). Hamsters and rats excrete somewhat more by this route, and the dog very little. This is illustrated in Fig. 10. It is of importance to note that very little of the radioactivity appears in the feces. This may be significant with regard to intestinal synthesis of the vitamin. 

Vitamin Bn is required in minute amounts, one microgram per day supplying the needs for the human body. However, absorption of this small amount of vitamin from the gut and transport to its sites of action requires special transport proteins. One of these, the intrinsic factor, is synthesized by cells of the intestinal mucosa and is utilized for absorption of vitamin Bn. Synthesis of the intrinsic factor is defective in some individuals, and is often inadequate in persons older than about 60 years. If untreated, this deficiency leads to pernicious anemia, a... 

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