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 following is strictly not a vitamin? 
Select and explain. 
A. Thiamine, B. Riboflavin, C. Niacin, D. Cobalamin
C: Niacin
Answer: C: Niacin 
Explanation: NIACIN IS NOT STRICTLY A VITAMIN Niacin was discovered as a nutrient during studies of pellagra. It is not strictly a vitamin since it can be synthesized in the body from the essential amino acid Reference: Harper; 30th edition; Page no: 556