What Is Alpha-Lipoic Acid (Thioctic Acid)?

Alpha-lipoic acid (ALA), also known as thioctic acid, is a sulfur-containing fatty acid that occurs naturally in cells as lipoate (the form ALA takes after it has reacted with something alkaline). It is an antioxidant and is sold over the counter as a dietary supplement, although its health benefits are a matter of controversy. It is not, strictly speaking, a vitamin because it is produced within the body.

History

• Lipoase, the form of ALA that exists in the human body, was discovered by I. C. Gunsalus (who referred to ALA as "pyruvate oxidation factor") at the University of Illinois Urbana-Champaign in 1948. L.J. Reed, at the University of Texas at Austin, later isolated ALA in pure form and determined its structure.

Biosynthesis

• ALA is synthesized in mitochondria (components of cells that convert sugars into energy) from octanoic acid (a fatty acid with an eight-carbon chain). In mitochondria, the lipoic acid binds to proteins.

Biological Function

• ALA is an enzyme cofactor (meaning it is essential to one or more enzyme functions). The particular enzyme complexes linked to APA are involved in glycolysis--the process by which cells convert sugars and starches into energy. The antioxidant abilities of ALA may help prevent oxygen damage to cells, although this has not been conclusively established. ALA is known to react with and neutralize free radicals, but only in vitro (in a test tube).

Dietary Intake

• Trace quantities of ALA are found in almost all foods. Foods with the highest amounts of lipoic acid are green, leafy vegetables (broccoli, spinach, collard greens, chard) and certain animal parts (heart, liver, kidney). It should be noted that the amount of ALA actually ingested (even from foods with relatively high ALA concentrations) is exceedingly small.

Supplements

• Dietary supplements containing ALA have been available since the 1990s. It is manufactured, marketed and sold as an herbal supplement. No standard dosage rates have been established. When taken as an antioxidant, ALA has been shown to prevent symptoms associated with vitamin C and vitamin E deficiencies.