There's more than a price difference. The vitamin C from China contains measurable levels of lead, cadmium, mercury, iron and other toxic metals. The FDA allows this slightly contaminated product to be sold in the US because the Recommended Daily Allowance for vitamin C is a mere 60 milligrams per day. Taken at that level, the toxic metals would, as the FDA sees it, do no harm. However, many users of vitamin C take 100--200 times the RDA. The cheap form of C would expose them to potentially toxic levels of heavy metal poisons. The highly refined top-quality product removes impurities to a virtually undetectable level. I buy my C from Bronson who ethically gives me the quality stuff. I know for a fact that the vitamin C sold by Prolongevity is also top quality. I've had clients who bought cheaper C than Bronson's and discovered it was not quite like Bronson's in appearance or taste. More importantly, it did not seem to have the same therapeutic effect. The distributors I've mentioned so far, Bronson, NOW, Cooper, Prolongevity and Vitamin Research Products are all knowledgeable about differences between actual manufacturers and are ethical, buying and reselling only high quality products. Other distributors I believe to be reputable include Twin Labs, Schiff and Plus. I know there are many other distributors with high ethic levels but I can not evaluate all their product lines. And as I've mentioned earlier, businesses come and go rather quickly, but I hope my book will be read for decades. I do know that I would be very reluctant to buy my vitamins at a discount department store or supermarket; when experimenting with new suppliers I have at times been severely disappointed. Co-enzyme Q-10. This substance is normally manufactured in the human body and is also found in minuscule amounts in almost every cell on Earth. For that reason it is also called "ubiquinone." But this vitamin has been only recently discovered, so as I write this book Co-enzyme Q-10 is not widely known. Q-10 is essential to the functioning of the mitochondria, that part of the cell that produces energy. With less Q-10 in heart cells, for example, the heart has less energy and pumps less. The same is true of the immune system cells, the liver cells, every cell. As we age the body is able to make less and less Q-10, contributing to the loss of energy frequently experienced with age, as well as the diminished effectiveness of the immune system, and a shortened life span.