C.N.C. Vitamins were originally elements found in natural foods.
Vitamin stands for vital-amines.
These essential parts of foods are the things that keep your birds alive along with minerals and the co-factors that are necessary for good health. Then they basically extracted each particular element from each food and tried to reproduce it chemically. Well, for one reason it's cheaper to synthesize than to actually go out and harvest it somewhere. And so a food that is synthesized turns out to be an incomplete source of nutrition. Conversely, when nature puts the food together it contains all the elements - vitamins, minerals, amino acids, etc.