{"id":178,"date":"2019-03-11T17:45:36","date_gmt":"2019-03-11T17:45:36","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/sunyltnutrition\/?post_type=chapter&p=178"},"modified":"2019-04-12T18:17:10","modified_gmt":"2019-04-12T18:17:10","slug":"7-3-water-soluble-vitamins","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/sunyltnutrition\/chapter\/7-3-water-soluble-vitamins\/","title":{"raw":"7.3: Water Soluble Vitamins","rendered":"7.3: Water Soluble Vitamins"},"content":{"raw":"

Nine vitamins are considered water soluble, including: vitamin C and all of the B vitamins (Riboflavin, Niacin, Thiamin, B6<\/sub>, Folate, B12<\/sub>, Pantothenic\u00a0Acid and Biotin). In contrast to the four\u00a0Fat-Soluble Vitamins<\/a>, Water-soluble vitamins dissolve easily in water and, in general, are readily excreted from the body, to the degree that urinary output is a strong predictor of vitamin consumption.\u00a0Because they are not as readily stored, more consistent intake is important.\u00a0<\/span>Many types of water-soluble vitamins are synthesized by bacteria.<\/p>\r\n\r\n

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7.3A: Vitamin B\u2081 (Thiamine)<\/h2>\r\n<\/header>
Thiamine, also known as\u00a0thiamin\u00a0or\u00a0vitamin B1, is a\u00a0vitamin\u00a0found in food and used as a\u00a0dietary supplement.\u00a0As a supplement it is used to treat and prevent\u00a0thiamine deficiency\u00a0and disorders that result from it, including\u00a0beriberi,\u00a0Korsakoff's syndrome, and\u00a0Korsakoff's psychosis. Other uses include\u00a0maple syrup urine disease\u00a0and\u00a0Leigh's disease. It is taken\u00a0by mouth\u00a0or by\u00a0injection. Side effects are generally few.\u00a0Allergic reactions\u00a0including\u00a0anaphylaxis\u00a0may occur. Thiamine is in the\u00a0B complex\u00a0family. It is needed for the\u00a0metabolism\u00a0of\u00a0carbohydrates.[1]\u00a0As people are unable to make it, thiamine is an\u00a0essential nutrient. Food sources include\u00a0whole grains, meat, and fish.Thiamine was discovered in 1897 and is\u00a0on the\u00a0World Health Organization's List of Essential Medicines, the most effective and safe medicines needed in a\u00a0health system.\u00a0Thiamine is available as a\u00a0generic medication\u00a0and\u00a0over the counter.\u00a0The wholesale cost in the\u00a0developing world\u00a0is about 2.17 USD per one gm vial.\u00a0In the United States a month of replacement is less than 25 USD.\u00a0Some countries require its addition to certain foods such as\u00a0grains. Thiamine is used to treat\u00a0thiamine deficiency\u00a0which can prove fatal.\u00a0In less-severe cases, nonspecific signs include\u00a0malaise, weight loss, irritability and confusion.Thiamine is a colorless\u00a0organosulfur compound\u00a0with a\u00a0chemical formula\u00a0C<\/span><\/span><\/span><\/span>12<\/span><\/span><\/span><\/span>H<\/span><\/span><\/span><\/span>17<\/span><\/span><\/span><\/span>N<\/span><\/span><\/span><\/span>4<\/span><\/span><\/span><\/span>OS<\/span><\/span><\/span>C12H17N4OS<\/span><\/span>\u00a0(Figure\u00a07.3<\/span>A<\/span>.<\/span>1<\/span><\/span><\/span><\/span><\/span>7.3A.1<\/span><\/span>). Its structure consists of an\u00a0aminopyrimidine\u00a0and a\u00a0thiazole\u00a0ring linked by a\u00a0methylene bridge. The thiazole is substituted with methyl and hydroxyethyl side chains. Thiamine is\u00a0soluble\u00a0in\u00a0water,\u00a0methanol, and\u00a0glycerol\u00a0and practically insoluble in less polar\u00a0organic solvents. It is stable at acidic pH, but is unstable in alkaline solutions. Thiamine, which is a\u00a0N-heterocyclic carbene, can be used in place of\u00a0cyanide\u00a0as a catalyst for\u00a0benzoin condensation.\u00a0Thiamine is unstable to heat, but stable during frozen storage.[citation needed]\u00a0It is unstable when exposed to ultraviolet light[9]\u00a0and gamma irradiation.\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"346\"]\"346px-Thiamin.svg.png\" Figure\u00a0<\/em>7.3A.1<\/strong>: Structure of thiamine<\/em>[\/caption]\r\n\r\nThiamin is found in a wide variety of processed and whole foods, with edible seeds,\u00a0legumes,\u00a0rice\u00a0and\u00a0processed foods, such as\u00a0breakfast cereals, having among the highest contents.\u00a0Some other foods naturally rich in thiamin are\u00a0corn flour, pork,\u00a0pecans\u00a0and\u00a0spinach.\r\n
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Dietary Reference Intakes<\/h3>\r\n

The Food and Nutrition Board of the U.S. Institute of Medicine updated Estimated Average Requirements (EARs) and Recommended Dietary Allowances (RDAs) for thiamine in 1998. The current EARs for thiamine for women and men ages 14 and up are 0.9\u00a0mg\/day and 1.0\u00a0mg\/day, respectively; the RDAs are 1.1 and 1.2\u00a0mg\/day. RDAs are higher than EARs so as to identify amounts that will cover people with higher than average requirements. RDA for pregnancy equals 1.4\u00a0mg\/day. RDA for lactation equals 1.4\u00a0mg\/day. For infants up to 12 months the Adequate Intake (AI) is 0.2-0.3\u00a0mg\/day. and for children ages 1\u201313 years the RDA increases with age from 0.5 to 0.9\u00a0mg\/day.<\/p>\r\n

As for safety, the Food and Nutrition Board of the U.S. Institute of Medicine sets Tolerable Upper Intake Levels (known as ULs) for vitamins and minerals when evidence is sufficient. In the case of thiamine there is no UL, as there is no human data for adverse effects from high doses. The European Food Safety Authority reviewed the same safety question and also reached the conclusion that there was not sufficient evidence to set a UL for thiamine. Collectively the EARs, RDAs and ULs are referred to as\u00a0Dietary Reference Intakes.<\/p>\r\n

For U.S. food and dietary supplement labeling purposes the amount in a serving is expressed as a percent of Daily Value (%DV). For thiamine labeling purposes 100% of the Daily Value was 1.5\u00a0mg, but as of May 2016 it has been revised to 1.2\u00a0mg. A table of the pre-change adult Daily Values is provided at\u00a0Reference Daily Intake. Food and supplement companies have until July 28, 2018 to comply with the change.<\/p>\r\n\r\n<\/div>\r\n

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Antagonists<\/h3>\r\nThiamine in foods can be degraded in a variety of ways.\u00a0Sulfites, which are added to foods usually as a preservative,\u00a0will attack thiamine at the methylene bridge in the structure, cleaving the pyrimidine ring from the thiazole ring.\u00a0The rate of this reaction is increased under acidic conditions. Thiamine is degraded by thermolabile\u00a0thiaminases\u00a0(present in raw fish and shellfish). Some thiaminases are produced by bacteria. Bacterial thiaminases are cell surface enzymes that must dissociate from the membrane before being activated; the dissociation can occur in ruminants under acidotic conditions. Rumen bacteria also reduce sulfate to sulfite, therefore high dietary intakes of sulfate can have thiamine-antagonistic activities.\r\n\r\nPlant thiamine antagonists are heat-stable and occur as both the ortho- and para-hydroxyphenols. Some examples of these antagonists are\u00a0caffeic acid,\u00a0chlorogenic acid, and\u00a0tannic acid. These compounds interact with the thiamine to oxidize the thiazole ring, thus rendering it unable to be absorbed. Two flavonoids,\u00a0quercetin\u00a0and\u00a0rutin, have also been implicated as thiamine antagonists.\r\n\r\n<\/div>\r\n
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Absorption<\/h3>\r\n

Thiamine is released by the action of phosphatase and pyrophosphatase in the upper small intestine. At low concentrations, the process is carrier-mediated, and, at higher concentrations, absorption occurs via passive diffusion. Active transport is greatest in the jejunum and ileum; but, active transport can be inhibited by alcohol consumption and by folic deficiency.\u00a0Decline in thiamine absorption occurs at intakes above 5\u00a0mg\/day.\u00a0The cells of the intestinal mucosa have thiamine pyrophosphokinase activity, but it is unclear as to whether the enzyme is linked to active absorption. The majority of thiamine present in the intestine is in the pyrophosphorylated form ThDP, but when thiamine arrives on the serosal side of the intestine it is often in the free form. The uptake of thiamine by the mucosal cell is likely coupled in some way to its phosphorylation\/dephosphorylation. On the serosal side of the intestine, evidence has shown that discharge of the vitamin by those cells is dependent on Na+<\/sup>-dependent ATPase.<\/p>\r\n

Uptake of thiamine by cells of the blood and other tissues occurs via active transport and passive diffusion.\u00a0The brain requires much more thiamine than other tissues of the body. Much of ingested thiamine never reaches the brain because of passive diffusion and the\u00a0blood\u2013brain barrier. About 80% of intracellular thiamine is phosphorylated and most is bound to proteins. In some tissues, thiamine uptake and secretion appears to be mediated by a soluble thiamine transporter that is dependent on Na+<\/sup>\u00a0and a transcellular proton gradient.<\/p>\r\n

Human storage of thiamine is about 25 to 30\u00a0mg, with the greatest concentrations in skeletal muscle, heart, brain, liver, and kidneys. ThMP and free (unphosphorylated) thiamine is present in plasma, milk, cerebrospinal fluid, and, it is presumed, all extracellular fluids. Unlike the highly phosphorylated forms of thiamine, ThMP and free thiamine are capable of crossing cell membranes. Thiamine contents in human tissues are less than those of other species.<\/p>\r\n\r\n<\/div>\r\n

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Contributors<\/h3>\r\n