Lipoic acid helps protect against oxidative stress generated by high glucose levels. Alpha-lipoic acid consists of two different forms (isomers) that have vastly different properties. The "R" form is the biologically active component (native to the body) that is responsible for lipoic acid's phenomenal antioxidant effect. The "S" form is produced from chemical manufacture and is not very biologically active. Typical alpha-lipoic acid supplements consist of the "R" and "S" form in a 50/50 ratio. That means a 100 mg alpha-lipoic acid supplement is providing 50 mg of the biologically active "R" form.