This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: vitamins, Subject name: Biochemistry
Which of the soluble vitamin is synthesized in the body? 
Select and explain. 
A. Thiamine, B. Vitamin C, C. Niacin, D. Pyridoxine
C: Niacin
Answer: C: Niacin 
Explanation: Not strictly a Vitamin Can be synthesized from Tryptophan Dietary nicotinamide, niacin and tryptophan (an essential amino acid) contribute to the synthesis of the coenzymes- nicotinamide adenine dinucleotide (NAD+) and nicotinamide adenine dinucleotide phosphate (NADP+) Nicotinamide is deaminated in the body to niacin Tryptophan produces quinolinate which then forms nicotinate mononucleotide and, ultimately, NAD+ and NADP+ Sixty milligrams of tryptophan is equivalent to 1 mg of niacin for the synthesis of niacin coenzymes ref Satyanarayana biochemistry 4th ed page 140