2.
sources - 1. The point at which something springs into being or from which it derives or is obtained.2. The point of origin, such as a spring, of a stream or river. See Synonyms at origin 3. To specify the origin of (a communication); document: The report is thoroughly sourced.
a doctor - a licensed medical practitioner. A person who holds Ph.D. degree (or the equivalent) from an academic institution
vitamin - any of a group of organic substances in small quantities to normal metabolism