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==What is Vitamin B3 (Niacin)?==

==What is Vitamin B3 (Niacin)?==

Vitamin B₃, also called niacin, is an essential '''water-soluble''' vitamin that participates as a [[Nutrition Glossary#Cofactor|cofactor]] in [[Sugars - Nutrition|glucose]], [[Fatty Acids Overview - Nutrition|fatty acid]] and [[Amino Acids Overview - Nutrition|amino acid]] metabolism. The term niacin is used to describe a number of compounds that have biological activity associated with nicotinamide, including nicotinic acid, and a variety of pyridine nucleotide structures. Nicotinic acid and nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP) are metabolized to nicotinamide within the intestinal lumen and absorbed across the intestinal mucosa by either carrier-mediated transport or passive diffusion. Once in the enterocyte nicotinamide is either released as free nicotinamide or converted to NAD for use by the cell. Niacin derivatives are filtered by the renal tubules, with some active reabsorption during periods of low intake.<ref name="McCormick">McCormick DB. (2000) '''Niacin, Riboflavin, and Thiamin. In Biochemical and physiological aspects of human nutrition. '''2000 ''Philadelphia, PA: WB Saunders Company'' p. 459-468.</ref>  

Vitamin B₃, also called niacin, is an essential '''water-soluble''' vitamin that participates as a [[Nutrition Glossary#Cofactor|cofactor]] in [[Sugars - Nutrition|glucose]], [[Fatty Acids Overview - Nutrition|fatty acid]] and [[Amino Acids Overview - Nutrition|amino acid]] metabolism. The term niacin is used to describe a number of compounds that have biological activity associated with nicotinamide, including nicotinic acid, and a variety of pyridine nucleotide structures. Nicotinic acid and nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP) are metabolized to nicotinamide within the intestinal lumen and absorbed across the intestinal mucosa by either carrier-mediated transport or passive diffusion. Once in the enterocyte nicotinamide is either released as free nicotinamide or converted to NAD for use by the cell. Niacin derivatives are filtered by the [[Nephron Microscopic Anatomy#Proximal Tubule|renal tubules]], with some active reabsorption during periods of low intake.<ref name="McCormick">McCormick DB. (2000) '''Niacin, Riboflavin, and Thiamin. In Biochemical and physiological aspects of human nutrition. '''2000 ''Philadelphia, PA: WB Saunders Company'' p. 459-468.</ref>  

Like most animals, dogs can synthesise a certain amount of niacin from the essential amino acid [[Tryptophan - Nutrition|tryptophan]]. The tryptophan metabolite α-amino-β-carboxymuconic-ε-semialdahyde can be utilized in one of two pathways; it can be degraded by picolinic carboxylase to form acetyl-CoA and CO₂ or it can be used to produce nicotinamide. Cats, unlike dogs, are unable to synthesise significant levels of niacin from tryptophan because they have very high activity of the enzyme picolinic carboxylase which results in rapid catabolism of trypophan to acetyl-CoA and CO₂.<ref name="NRC">National Research Council (NRC) (2006)''' Vitamins. In Nutrient Requirements for Dogs and Cats.''' 2006 ''Washington, DC: National Academies Press ''p.220-223.</ref> As such, cats require preformed niacin in the diet.<ref name="Morris">Morris, J.G. (2002) '''Idiosyncratic nutrient requirements of cats appear to be diet-induced evolutionary adaptations.''''' Nutr Res Rev ''2002;15; 153-168.</ref>

Like most animals, '''dogs can synthesise a certain amount of niacin from the essential amino acid [[Tryptophan - Nutrition|tryptophan]]'''. The tryptophan metabolite α-amino-β-carboxymuconic-ε-semialdahyde can be utilized in one of two pathways; it can be degraded by picolinic carboxylase to form acetyl-CoA and CO₂ or it can be used to produce nicotinamide. '''Cats, unlike dogs, are unable to synthesise significant levels of niacin from tryptophan''' because they have very high activity of the enzyme picolinic carboxylase which results in rapid catabolism of trypophan to acetyl-CoA and CO₂.<ref name="NRC">National Research Council (NRC) (2006)''' Vitamins. In Nutrient Requirements for Dogs and Cats.''' 2006 ''Washington, DC: National Academies Press ''p.220-223.</ref> As such, cats require preformed niacin in the diet.<ref name="Morris">Morris, J.G. (2002) '''Idiosyncratic nutrient requirements of cats appear to be diet-induced evolutionary adaptations.''''' Nutr Res Rev ''2002;15; 153-168.</ref>

==Why is it Important?==

==Why is it Important?==

==Consequences of Niacin Deficiency==

==Consequences of Niacin Deficiency==

1. Dogs: Chronic niacin deficiency in puppy and adult dogs (also called “black-tongue”) causes anorexia, weight loss, erythema of the oral mucosa with progression to inflammation and ulceration, ptyalism, bloody diarrhoea, and eventually death.2

====Dogs:====

2. Cats: Cats and kittens fed niacin deficient diets develop anorexia, fever, erythema of oral mucosa and tongue with eventual ulceration, weight loss, and death within the 2-3 weeks.8,9

Chronic niacin deficiency in puppy and adult dogs (also called “black-tongue”) causes anorexia, weight loss, erythema of the oral mucosa with progression to inflammation and ulceration, ptyalism, bloody diarrhoea, and eventually death.2

Niacin is prone to degradation with heat processing. Conditions associated with diuresis (e.g., chronic disease, such as renal disease or diabetes, or therapeutic intervention, such as intravenous fluids or increased water intake with management of lower urinary diseases) can result in increased loss of niacin and may increase daily requirements. Patient on chronic haemodialysis are at an increased risk for developing a deficiency.  

====Cats:====

Cats and kittens fed niacin deficient diets develop anorexia, fever, erythema of oral mucosa and tongue with eventual ulceration, weight loss, and death within the 2-3 weeks.8,9

Niacin is prone to degradation with heat processing. Conditions associated with diuresis (e.g., chronic disease, such as renal disease or [[Diabetes Insipidus|diabetes]], or therapeutic intervention, such as intravenous fluids or increased water intake with management of [[Cystitis|lower urinary diseases]]) can result in increased loss of niacin and may increase daily requirements. Patient on chronic haemodialysis are at an increased risk for developing a deficiency.  

Toxicity

==Toxicity==

There are no published studies evaluating niacin toxicity in cats. In dogs one study reported bloody diarrhoea in 2 dogs that were fed approximately x250 the adult requirement, and chronic exposure (11 days) resulted in death.10 In humans, where it is used to help manage hypercholesterolemia, a high intake niacin (x25 the minimum requirement)  can cause peripheral vasodilation (i.e., “flushing”).5 This side effect of therapeutic niacin has not been evaluated in dogs.

There are no published studies evaluating niacin toxicity in cats. In dogs one study reported bloody diarrhoea in 2 dogs that were fed approximately x250 the adult requirement, and chronic exposure (11 days) resulted in death.10 In humans, where it is used to help manage hypercholesterolemia, a high intake niacin (x25 the minimum requirement)  can cause peripheral vasodilation (i.e., “flushing”).5 This side effect of therapeutic niacin has not been evaluated in dogs.

Dietary Sources

 

==Dietary Sources==

Niacin is naturally occurring in muscle and organ meats and pulses (i.e., legumes). Dietary niacin is typlically found in the form of nicotinic acid in plant based materials, and as NAD or NADP in animal based materials. Certain whole grains such as corn and sorghum  have a relatively high niacin content, but in these foods niacin is concentrated in the bran and germ layers and has poor [[Nutrition Glossary#Bioavailability|bioavailability]] (i.e., highly bound within the cell), making them  a poor source of dietary niacin. Niacin is also sensitive to degradation with heating and additional supplementation is required with commercial pet foods.  

Niacin is naturally occurring in muscle and organ meats and pulses (i.e., legumes). Dietary niacin is typlically found in the form of nicotinic acid in plant based materials, and as NAD or NADP in animal based materials. Certain whole grains such as corn and sorghum  have a relatively high niacin content, but in these foods niacin is concentrated in the bran and germ layers and has poor [[Nutrition Glossary#Bioavailability|bioavailability]] (i.e., highly bound within the cell), making them  a poor source of dietary niacin. Niacin is also sensitive to degradation with heating and additional supplementation is required with commercial pet foods.  

Diagnosing Niacin Deficiency

 

==Diagnosing Niacin Deficiency==

Diagnosis of niacin deficiency can be made using the nicotinamide loading test, which measures urine excretion of niacin metabolites;11 though not routinely tested through veterinary reference laboratories.  

Diagnosis of niacin deficiency can be made using the nicotinamide loading test, which measures urine excretion of niacin metabolites;11 though not routinely tested through veterinary reference laboratories.  

Diagnosis is also made on clinical signs consistent with deficiency and evaluation of diet.

Diagnosis is also made on clinical signs consistent with deficiency and evaluation of diet.