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.