This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nutrition and health, Subject name: Social & Preventive Medicine
[{'content': 'Niacin is synthesised from - \nSelect and explain. \nA. Tryptophan, B. Tyrosine, C. Methionine, D. Phenylalanine', 'role': 'user'}, {'content': "Answer: A \nExplanation: - niacin is essential for the metabolism of carbohydrate, fat and protein. It is also essential for the normal functioning of skin , intestinal and nervous system. - it differs from other other B complex vitamins that an essential amino acid tryptophan serves as its precursor. Reference : Park's textbook of preventive and social medicine, 23rd edition, pg no:619 <\\p>", 'role': 'assistant'}]