chapter 13- thiamin, niacin, and pantothenic acid

water-soluble vitamins

essential organic substances needed in small amounts for the normal function, growth, and maintenance of body tissues

all B-vitamins form

coenzymes- which are small, organic molecules that are a type of cofactor

cofactors

combine with inactive enzymes to form active enzymes that are able to catalyze specific reactions, metals are types of cofactors

in the US nearly all bread and cereal products made from milled grains are enriched with

thiamin, riboflavin, niacin, and folic acid

foods made with enriched and fortified grains have less

vitamin B6, potassium, magnesium, zinc, fiber, and phytochemicals than those from whole grains because refined grains lack the nutrient rich germ and bran

thiamin- food sources

pork, sunflower seeds, and legumes

thiamin- absorption and transportation

readily absorbed in the small intestine by a sodium-dependent active absorption process, transported by RBCs in its coenzyme form

thiamin- storage

little stored, small reserve found in muscle, brain, liver, and kidney

thiamin- function

coenzyme thiamin pyrophosphate (TPP) is required for the metabolism of carbohydrates and branched-chain amino acids

thiamin- people at risk for deficiency

people with heart failure, GI diseases, critical illness, eating disorders, and obesity

thiamin deficiency- beriberi

develop extreme weakness, paralysis, and fatigue, often dying within several months

niacin synthesis

60mg to dietary tryptophan needed to make 1mg of niacin, riboflavin and B6 coenzymes required

niacin and protein

protein is about 1% tryptophan so 1g of protein provides 10mg of tryptophan

niacin RDA

expressed as niacin equivalents (NE) to account for preformed niacin in foods and niacin synthesized from tryptophan

niacin- absorption

nicotinic acid and nicotinamide are readily absorbed from the stomach and small intestine by active transport and passive diffusion, so generally all niacin consumed is absorbed

niacin- bioavalibility

low in some grains, especially corn, because niacin is tightly bound to protein, so less than 30% can be absorbed

niacin- transport

via the portal vein to the liver where it’s stored or delivered to the body’s cells, covered to its coenzyme forms in all tissues, any excess niacin is excreted in the urine

niacin- functions

coenzyme forms of niacin, NAD⁺ and NADP⁺ are active participants in oxidation-reduction reactions, cellular metabolic pathways that produce ATP

niacin- deficiency

pellagra, corn-based diets not treated with alkali, corn contain little tryptophan

niacin- pharmacological use

increase HDL-cholesterol, lower LDL-cholesterol and triglyceride levels with the aim of reducing the risk of stroke and heart attack, no longer recommended

pantothenic acid

present in all body cells and is supplied by a wide variety of food, part of acyl carrier protein (ACP) used in many biosynthetic reactions and coenzyme A (CoA) which is used in energy metabolism

pantothenic acid- food sources

meat, milk, vegetables, mushrooms, peanuts, egg yolks, yeast, broccoli, and soy milk. unprocessed foods are better source because milling, refining, freezing, heating, and canning can reduce pantothenic acid in foods

pantothenic acid- absorption and transportation

CoA in the diet is released during digestion in the small intestine, absorbed and transported throughout the body bound the RBCs, storage is minimal, excreted via urine

pantothenic acid- functions

CoA is essential in forming acetyl-CoA from the breakdown of carbs, protein, alcohol, and fat; enter citric acid cycle, beta-oxidation, building block used to build fatty acids, cholesterol bile acids, and steroid hormones

pantothenic acid- deficiency

rare, symptoms include headache, fatigue, impaired muscle coordination, burning hands and feet, and GI tract disturbances