Alpha-lipoic acid (ALA) is a sulfur-containing fatty acid that performs vitamin-like roles in the body. Also known as "lipoic acid" or "thioctic acid," ALA functions, in a similar way to B complex vitamins, as a co-enzyme in the metabolism of carbohydrates that produces energy inside cells for the body’s metabolic needs. ALA is required for synthesis of "acetyl CoA," a key metabolite in the cellular process that turns glucose (blood sugar) into energy. Because the body produces ALA on its own, it is not classified as a true vitamin. As with other so-called "non-essential" nutrients, however, internal ALA production may not always be optimal. Alpha-lipoic acid functions as both a water-soluble and fat-soluble antioxidant. (Antioxidants neutralize free-radicals, normal by-products of metabolism that, while necessary at normal levels, may damage tissues over time if not properly kept in check by antioxidants.) ALA’s ability to act upon free radicals in both a watery and fatty environment makes it a highly versatile antioxidant. In the body, alpha-lipoic acid can be converted (reduced) to DHLA, or dihydrolipoic acid. Together, these two forms of ALA make up a "redox couple," which means that each form can chemically change into the other and back again. DHLA also functions as an antioxidant.