Food, Nutrition & Diet Therapy, Krause
W.B. Saunders, Co., 1979, 6th. Ed., p.18.
Reprinted with permission
Lipoic acid, a fat soluble, sulfur-containing fatty acid, is not a true vitamin, since it can be synthesized in the body. It functions as a coenzyme and is essential together with the thiamin-containing enzyme, pyrophosphatase (TPP), for reactions in carbohydrate metabolism which convert pyruvic acid to acetyl-coenzyme A. Lipoic acid with two sulfur bonds combines with the TPP to reduce pyruvate to active acetate. It joins the intermediary products of protein and fat metabolism in the Krebs cycle in the reactions involved in producing energy from these nutrients. A metal ion (magnesium or calcium) is involved in this oxidative decarboxylation along with vitamins, thiamin, pantothenic acid, niacin, riboflavin and lipoic acid.
No dietary requirements for lipoic acid for humans is known. The amounts needed to participate in the reactions in the tissues may be synthesized in the body. It is found in liver and yeast.