WHOLE VS. FRACTIONATED
OK, natural vs. synthetic. Let's start with Vitamin C. Most sources equate vitamin C with ascorbic acid, as though they were the same thing. They're not. Ascorbic acid is an isolate, a fraction, a distillate of naturally occurring vitamin C. In addition to ascorbic acid, vitamin C must include rutin, bioflavonoids, Factor K, Factor J, Factor P, Tyrosinase, Ascorbinogen, and other components. In addition, mineral co-factors must be available in proper amounts.
If any of these parts are missing, there is no vitamin C, no vitamin activity. When some of them are present, the body will draw on its own stores to make up the differences, so that the whole vitamin may be present. Only then will vitamin activity take place, provided that all other conditions and co-factors are present. Ascorbic acid is described merely as the "antioxidant wrapper" portion of vitamin C; ascorbic acid protects the functional parts of the vitamin from rapid oxidation or breakdown. (Somer p 58 "Vitamin C: A Lesson in Keeping An Open Mind" The Nutrition Report)