{"id":745,"date":"2017-10-26T16:20:06","date_gmt":"2017-10-26T16:20:06","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/sunynutrition\/?post_type=chapter&p=745"},"modified":"2017-11-14T16:19:38","modified_gmt":"2017-11-14T16:19:38","slug":"10-5-niacin","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-nutrition\/chapter\/10-5-niacin\/","title":{"raw":"10.5 Niacin","rendered":"10.5 Niacin"},"content":{"raw":"
\r\n\r\nThere are two forms of niacin: nicotinic acid and nicotinamide (aka niacinamide), that have a carboxylic acid group or amide group, respectively. The structure of nicotinic acid and nicotinamide are shown below.\r\n
\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"344\"]\"\" Figure 10.51 Structure of nicotinic acid1<\/sup>[\/caption]\r\n\r\n<\/div>\r\n
\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"660\"]\"\" Figure 10.52 Structure of nicotinamide2<\/sup>[\/caption]\r\n\r\n<\/div>\r\nNiacin is important for the production of two cofactors: nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP+). The structure of NAD is shown below; you can clearly see the nicotinamide at the top right of the molecule.\r\n
\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"363\"]\"\" Figure 10.53 Structure of NAD3<\/sup>[\/caption]\r\n\r\n<\/div>\r\nNAD is reduced to form NADH, as shown below.\r\n
\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"760\"]\"\" Figure 10.54 Reduction of NAD to NADH4<\/sup>[\/caption]\r\n\r\n<\/div>\r\nThe structure of NADP+ is exactly the same as NAD, except it has an extra phosphate group off the bottom of the structure, as shown below.\r\n
\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"358\"]\"\" Figure 10.55 Structure of NADP+5<\/sup>[\/caption]\r\n\r\n<\/div>\r\nLike NAD, NADP+ can be reduced to NADPH.\r\n\r\nNiacin is unique in that it can be synthesized from the amino acid tryptophan as shown below. An intermediate in this synthesis is kynurenine. Many reactions occur between this compound and niacin, and riboflavin and vitamin B6 are required for two of these reactions.\r\n
\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"1108\"]\"\" Figure 10.56 Tryptophan can be used to synthesize niacin6<\/sup>[\/caption]\r\n\r\n<\/div>\r\nTo account for niacin synthesis from tryptophan, niacin equivalents (NE) were created by the DRI committee to account for the amount of niacin in foods as well as their tryptophan content. It takes approximately 60 mg of tryptophan to make 1 mg of niacin. Thus, the conversions to niacin equivalents are:\r\n\r\n1 mg Niacin = 1 NE\r\n\r\n60 mg Tryptophan = 1 NE\r\n\r\nThe tryptophan levels of most foods is not known, but a good estimate is that tryptophan is 1% of amino acids in protein7<\/sup>. Thus, lets take peanut butter, smooth style, with salt as an example8<\/sup>.\r\n\r\nThe peanut butter contains 13.403 mg of niacin and 25.09 g of protein8<\/sup>.\r\n\r\nStep 1: Calculate the amount of tryptophan:\r\n\r\n25.09 g X 0.01 (the numerical value of 1%) = 0.2509g of tryptophan\r\n\r\nStep 2: Convert Grams to Milligrams\r\n\r\n0.2509 g X 1000 mg\/g = 250.9 mg of tryptophan\r\n\r\nStep 3: Calculate NE from tryptophan\r\n\r\n250.9 mg of tryptophan\/(60 mg of tryptophan\/1 NE) = 4.182 NE\r\n\r\nStep 4: Add NEs together\r\n\r\n13.403 NE (from niacin) + 4.182 (from tryptophan) = 17.585 NE\r\n\r\nMost niacin we consume is in the form of nicotinamide and nicotinic acid9<\/sup>, and in general is well absorbed using an unresolved carrier10<\/sup>. However, in corn, wheat, and certain other cereal products, niacin bioavailability is low. In these foods, some niacin (~70% in corn) is tightly bound, making it unavailable for absorption. Treating the grains with a base frees the niacin and allows it to be absorbed. After absorption nicotinamide is the primary circulating form7,9<\/sup>.\r\n\r\nSubsections:\r\n\r\n10.51 Niacin Functions<\/a>\r\n\r\n10.52 Niacin Deficiency & Toxicity<\/a>\r\n\r\n

References & Links<\/h3>\r\n\r\n1. http:\/\/en.wikipedia.org\/wiki\/File:Niacinstr.png\r\n\r\n2. http:\/\/en.wikipedia.org\/wiki\/File:Nicotinamide_structure.svg\r\n\r\n3. http:\/\/en.wikipedia.org\/wiki\/File:NAD%2B_phys.svg\r\n\r\n4. http:\/\/en.wikipedia.org\/wiki\/File:NAD_oxidation_reduction.svg\r\n\r\n5. http:\/\/en.wikipedia.org\/wiki\/File:NADP%2B_phys.svg\r\n\r\n6. https:\/\/commons.wikimedia.org\/wiki\/File:Nicotinic_acid_biosynthesis2.png\r\n\r\n7. Byrd-Bredbenner C, Moe G, Beshgetoor D, Berning J. (2009) Wardlaw's perspectives in nutrition. New York, NY: McGraw-Hill.\r\n\r\n8. http:\/\/www.nal.usda.gov\/fnic\/foodcomp\/search\/\r\n\r\n9. Gropper SS, Smith JL, Groff JL. (2008) Advanced nutrition and human metabolism. Belmont, CA: Wadsworth Publishing.\r\n\r\n10. Said H, Mohammed Z. (2006) Intestinal absorption of water-soluble vitamins: An update. Curr Opin Gastroenterol 22(2): 140-146.\r\n\r\n<\/div>","rendered":"
\n

There are two forms of niacin: nicotinic acid and nicotinamide (aka niacinamide), that have a carboxylic acid group or amide group, respectively. The structure of nicotinic acid and nicotinamide are shown below.<\/p>\n

\n
\"\"<\/p>\n

Figure 10.51 Structure of nicotinic acid1<\/sup><\/p>\n<\/div>\n<\/div>\n

\n
\"\"<\/p>\n

Figure 10.52 Structure of nicotinamide2<\/sup><\/p>\n<\/div>\n<\/div>\n

Niacin is important for the production of two cofactors: nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP+). The structure of NAD is shown below; you can clearly see the nicotinamide at the top right of the molecule.<\/p>\n

\n
\"\"<\/p>\n

Figure 10.53 Structure of NAD3<\/sup><\/p>\n<\/div>\n<\/div>\n

NAD is reduced to form NADH, as shown below.<\/p>\n

\n
\"\"<\/p>\n

Figure 10.54 Reduction of NAD to NADH4<\/sup><\/p>\n<\/div>\n<\/div>\n

The structure of NADP+ is exactly the same as NAD, except it has an extra phosphate group off the bottom of the structure, as shown below.<\/p>\n

\n
\"\"<\/p>\n

Figure 10.55 Structure of NADP+5<\/sup><\/p>\n<\/div>\n<\/div>\n

Like NAD, NADP+ can be reduced to NADPH.<\/p>\n

Niacin is unique in that it can be synthesized from the amino acid tryptophan as shown below. An intermediate in this synthesis is kynurenine. Many reactions occur between this compound and niacin, and riboflavin and vitamin B6 are required for two of these reactions.<\/p>\n

\n
\"\"<\/p>\n

Figure 10.56 Tryptophan can be used to synthesize niacin6<\/sup><\/p>\n<\/div>\n<\/div>\n

To account for niacin synthesis from tryptophan, niacin equivalents (NE) were created by the DRI committee to account for the amount of niacin in foods as well as their tryptophan content. It takes approximately 60 mg of tryptophan to make 1 mg of niacin. Thus, the conversions to niacin equivalents are:<\/p>\n

1 mg Niacin = 1 NE<\/p>\n

60 mg Tryptophan = 1 NE<\/p>\n

The tryptophan levels of most foods is not known, but a good estimate is that tryptophan is 1% of amino acids in protein7<\/sup>. Thus, lets take peanut butter, smooth style, with salt as an example8<\/sup>.<\/p>\n

The peanut butter contains 13.403 mg of niacin and 25.09 g of protein8<\/sup>.<\/p>\n

Step 1: Calculate the amount of tryptophan:<\/p>\n

25.09 g X 0.01 (the numerical value of 1%) = 0.2509g of tryptophan<\/p>\n

Step 2: Convert Grams to Milligrams<\/p>\n

0.2509 g X 1000 mg\/g = 250.9 mg of tryptophan<\/p>\n

Step 3: Calculate NE from tryptophan<\/p>\n

250.9 mg of tryptophan\/(60 mg of tryptophan\/1 NE) = 4.182 NE<\/p>\n

Step 4: Add NEs together<\/p>\n

13.403 NE (from niacin) + 4.182 (from tryptophan) = 17.585 NE<\/p>\n

Most niacin we consume is in the form of nicotinamide and nicotinic acid9<\/sup>, and in general is well absorbed using an unresolved carrier10<\/sup>. However, in corn, wheat, and certain other cereal products, niacin bioavailability is low. In these foods, some niacin (~70% in corn) is tightly bound, making it unavailable for absorption. Treating the grains with a base frees the niacin and allows it to be absorbed. After absorption nicotinamide is the primary circulating form7,9<\/sup>.<\/p>\n

Subsections:<\/p>\n

10.51 Niacin Functions<\/a><\/p>\n

10.52 Niacin Deficiency & Toxicity<\/a><\/p>\n

References & Links<\/h3>\n

1. http:\/\/en.wikipedia.org\/wiki\/File:Niacinstr.png<\/p>\n

2. http:\/\/en.wikipedia.org\/wiki\/File:Nicotinamide_structure.svg<\/p>\n

3. http:\/\/en.wikipedia.org\/wiki\/File:NAD%2B_phys.svg<\/p>\n

4. http:\/\/en.wikipedia.org\/wiki\/File:NAD_oxidation_reduction.svg<\/p>\n

5. http:\/\/en.wikipedia.org\/wiki\/File:NADP%2B_phys.svg<\/p>\n

6. https:\/\/commons.wikimedia.org\/wiki\/File:Nicotinic_acid_biosynthesis2.png<\/p>\n

7. Byrd-Bredbenner C, Moe G, Beshgetoor D, Berning J. (2009) Wardlaw’s perspectives in nutrition. New York, NY: McGraw-Hill.<\/p>\n

8. http:\/\/www.nal.usda.gov\/fnic\/foodcomp\/search\/<\/p>\n

9. Gropper SS, Smith JL, Groff JL. (2008) Advanced nutrition and human metabolism. Belmont, CA: Wadsworth Publishing.<\/p>\n

10. Said H, Mohammed Z. (2006) Intestinal absorption of water-soluble vitamins: An update. Curr Opin Gastroenterol 22(2): 140-146.<\/p>\n<\/div>\n\n\t\t\t

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Candela Citations<\/h3>\n\t\t\t\t\t
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