Lipoic acid ((R)-(+)-α-Lipoic acid) is the form biosynthesized in humans which is essential for aerobic metabolism. Lipoic acid ((R)-(+)-α-Lipoic acid) is the nutritionally and therapeutically preferred form due to its "vitamin-like" role in metabolism. Lipoic acid ((R)-(+)-α-Lipoic acid) and S-(-)-α-Lipoic acid) constitute the racemic mixture Lipoic acid. Only the Lipoic acid ((R)-(+)-α-Lipoic acid) exists in nature and is an essential cofactor of four mitochondrial enzyme complexes. Lipoic acid ((R)-(+)-α-Lipoic acid) has been suggested to be nutritionally and therapeutically preferred form as antioxidant.