Final answer:
Niacin, or nicotonic acid, plays a critical role as a coenzyme for oxido-reductases, aiding in the metabolism of food and synthesis of fatty acids and cholesterol. Deficiency can lead to pellagra, which manifests as dermatitis, diarrhea, and dementia, and excessive intake can cause peptic ulcers and hyperglycemia. Adequate intake is typically met through diet and the recommended daily quantity is 15-20 mg.
Step-by-step explanation:
Nicotonic acid, also known as niacin, is an essential nutrient that is converted into its amide form niacinamide or nicotinamide in the body. Its chemical composition includes a pyridine ring with a carboxylic acid, which is vital for various biochemical processes.
One of the primary functions of niacin is to serve as a coenzyme in the form of NAD+ and NADP+ for oxido-reductases. These enzymes help in the enzymatic removal of hydrogen atoms where NAD+ facilitates the oxidation of food substances, while NADPH is crucial for reductase actions in fatty acid and cholesterol synthesis.
Deficiency of niacin can lead to a disease known as pellagra, characterized by the '3 Ds': Dermatitis, Diarrhoea, and Dementia. This can escalate to a fourth 'D', Death, if not properly treated. Despite being widely distributed in foods and rarely occurring, a deficiency might also result in symptoms like nausea, vomiting, gastrointestinal tract disorders, anemia, and even impaired growth.
The daily recommended intake of niacin ranges from 15-20 mg/day, which varies based on dietary protein since niacin can be synthesized from the amino acid tryptophan. Foods rich in niacin include liver, fish, beans, and peanuts.
While niacin is essential, it is crucial to avoid excessive intake as high doses can lead to peptic ulcers, hyperglycemia, dizziness, and gout, indicating the importance of not exceeding the Tolerable Upper Intake Levels (UL).