Quoted from The Hundred-Year Lie:

Studies of both vitamin C and vitamin E show that the naturally occurring forms are more absorbable by the body and more biologically active than synthetics.

The science studies demonstrating the superiority of naturally occurring vitamins over synthetics have been published in such journals as Annals of the New York Academy of Sciences, The American Journal of Clinical Nutrition, and Britain’s Royal Society of Chemistry. In a 1998 study at Oregon State University six volunteers were given 150-milligram doses of synthetic vitamin E and later the same dose of vitamin E from natural sources. Urine tests showed conclusively that the human body prefers natural vitamin E by its retention of it and by how quickly it excretes the synthetic version. Robert Acuff, director of the Center for Nutrition Research at East Tennessee State University, did a review of thirty published studies on the differences between natural and synthetic vitamin E and concluded that the natural form delivers twice the health benefits of synthetics because it is the one our bodies were designed to use.

Newspaper headlines in late 2004 trumpeted the news of a study published by Annals of Internal Medicine that found taking vitamin E supplements fails to prevent heart disease. A friend of mine in the vitamin industry pointed out that this study, like nearly every other health-related study of vitamins, used synthetic and not natural sources. Even the news coverage of this negative study indirectly alluded to such a bias. “Studies also show that healthy people who eat vitamin-rich food seem to have less heart disease,” read the Associated Press report. “Experts say that perhaps antioxidants [such as vitamin E] work when only in food.”

Naturally occurring substances seem to contain a “lifeforce” that synthetics cannot duplicate. That lifeforce is a product of synergy, and synthetics lack the capacity to induce natural synergies. With any vitamin there is an accompanying x-factor of supporting compounds, without which the beneficial effects on the body are diminished. Nobel Prize laureate Albert Szent-Györgyi was one of the first to notice how scurvy, a disease caused by vitamin C deficiency, could never be cured by the ascorbic acid component of vitamin C alone but required the complete matrix of vitamin C components found in food.

A friend of mine, Scott Treadway, has spent thirty years as an expert on vitamin formulation and draws a clear distinction between synthetic and natural. “Although we have been led to believe that ascorbic acid, a synthesized form of vitamin C, is really vitamin C, it is not. Alpha tocopherol is not vitamin E. Retinoic acid is not vitamin A. And so on through the other vitamins. Vast energy and resources have been expended to make these myths part of conventional wisdom. However, the truth is that vitamins are not individual molecular compounds. Vitamins are biological complexes. In addition to ascorbic acid, real vitamin C must include bioflavonoids [the natural pigments in fruits and vegetables] like hesperidin, rutin, quercetin, tannins, along with other naturally occurring compounds. Mineral cofactors must be available in proper amounts. If any of these parts are missing, there is no vitamin activity.

The Hundred-Year Lie by Randall Fitzgerald, pg. 137-38.