Antioxidant Clinical Trials
Clinical trials investigating the protective effects of high-dose vitamin E alone in PD patients have produced disappointing results. However, when vitamin E is administered with vitamin C, results show greater promise.
In 1987, researchers began testing whether alpha-tocopherol (vitamin E) and the drug selegiline (deprenyl) could slow PD progression.  The study, published in the New England Journal of Medicine, enrolled 800 patients with early-stage PD in a multicenter, placebo-controlled, double-blind clinical trial.Patients received either 2,000 IU/day alpha-tocopherol, 10 mg/day deprenyl, a combination of both, or placebo, for an average of 14 months. Patients were followed to determine if and when PD disability required levodopa therapy. Deprenyl inhibits monoamine oxidase, an enzyme that destroys dopamine. When deprenyl is combined with alpha-tocopherol, a free radical scavenger, they theoretically would act as antioxidants in different but complementary ways.
Results showed that deprenyl treatment alone or with alpha-tocopherol reduced the rate of disability requiring levodopa by 57 percent, but alpha-tocopherol alone did not produce a benefit. The slowed PD progression was attributed to deprenyl and not to any complementary actions of alpha-tocopherol.
A clinical trial at Columbia University College of Physicians and Surgeons in New York City investigated whether taking both vitamins C and E (alpha-tocopherol) could extend the time before levodopa treatment was required in 15 early-stage PD patients. 
The pilot study, designed to obtain experience with high doses of vitamins C (3,000 mg/day) and E (3,200 mg/day), had no control groups, but compared results to PD patients who did not receive antioxidants and were treated by another clinician. Results showed that the group taking both antioxidants lasted an additional 2.5 years before levodopa therapy was necessary.
1. Parkinson Study Group.
Effects of tocopherol and deprenyl on the progression of disability in early Parkinson's disease.
2. Fahn S.
An open trial of high-dose antioxidants in early Parkinson's disease.
Am J Clin Nut 1991;53:380S-2S.