There’s a big difference between natural and synthetic vitamins. Natural vitamins are extracted from whole food sources while synthetic vitamins are produced in a factory on the basis of purified raw materials. Natural vitamin extracts provide vitamins in forms that are recognized relatively easily by the body; they also contain essential cofactors that optimize performance and absorption. Synthetic vitamins, rather, come as isolated molecules bound together in artificially induced types of connections. Some of the latter compounds are not at all well-absorbed while others compounds are absorbed exceedingly well.

As for “cofactors” of natural vitamins, think, for example, of natural dyes based on plants, vegetables or fruits, and of other natural plant substances such as flavonoids and natural antioxidants. The big difference is immediately visible on comparing natural and synthetic powders. Synthetic vitamins almost always have a crystalline structure and are usually white, while natural vitamin powders just have a fine structure and come in different colors. Depending on specific situations one of the variants of vitamins, or perhaps a combination of both, can be chosen.

It is generally thought that the body sees no difference between synthetic and natural vitamins and that they have the same effects and working mechanisms. This is not true at all, however.

One study entitled "Natural vitamins may be superior to synthetic ones" (Med Hypotheses. 2000 Dec;55(6):461-9), pointed out the following:

“Bio-activity is a complex subject, and it should be understood that the absorption of vitamins, minerals and trace elements are dependent on a number of factors […].

1. There are several mechanisms that influence the absorption and the actual use of vitamins within the body.
2. Particle size is an important factor in the absorption of nutrients—smaller is better.
3. There are co-factors in foods which not only enhance absorption of nutrients, but also have a reciprocal effect on one another, and also on the non-absorbable components of food.
4. The physiochemical form of a nutrient during absorption and bio-activity plays an important role. Synthetic and natural vitamins are not always the same.
5. Most synthetic vitamins have a crystalline structure, while most natural vitamins have not.”

Synthetic vitamins do not qualify as food in any way, even though they are often labeled as "natural" and added to natural food sources. Synthetic vitamins are standardized and purified chemicals. In nature, vitamins are never isolated: they are invariably part of a food-vitamin complex.

The above information does not mean that vitamins, minerals and trace elements that are not derived from whole foods have no nutritional value. However, it is important to understand that there is a vital difference between the two forms, which may be very relevant for your purposes.