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A widely available dietary supplement, coenzyme Q10, has shown promising results in a clinical trial involving 80 patients with early Parkinson's disease, according to a recent article in the Archives of Neurology. In the trial—a multicenter, randomized, placebo-controlled, double-blind, and dosage-ranging trial—coenzyme Q10 was shown to be safe, well-tolerated, and significantly effective in slowing the progression of the neurological disorder. And it was clearly dose-dependent—that is, the larger the dose, the greater its effect.

"Our results are so encouraging that we have to emphasize that they still have to be confirmed by a Phase III clinical trial with a larger group of patients," said Dr. Flint Beal, Chairman of the Department of Neurology and Neuroscience at Weill Cornell Medical College and one of the authors of the article. He and his colleagues caution that the findings may not extend to patients with later stages of Parkinson's or to patients who are at risk but have not been diagnosed with the disorder. Furthermore, if too many people now buy coenzyme Q10 on their own, there may not be enough subjects for a rigorous Phase III trial.

Parkinson's disease affects about 500,000 people in the United States. It is caused by the loss of brain cells that produce the neurotransmitter dopamine. The symptoms are tremor, decreased balance and coordination, stiffness, slowing of movements, and sometimes difficulty swallowing and disturbed sleep. It is most common in the aging, but can also strike younger persons. Drugs like levodopa can ease the symptoms, but no treatment has been shown to slow the progression of the disease.

Coenzyme Q10 is believed to improve the action of mitochondria, which are the sources of energy in cells. Coenzyme Q10 is also an antioxidant: a chemical that neutralizes potentially harmful chemicals produced by metabolism. Previous studies by Dr. Beal and others have shown that in Parkinson's patients, the levels of coenzyme Q10 in the mitochondria are lower than normal, and that the mitochondrial function in these patients is impaired.

The patients in the trial were divided into four groups—one taking placebo and three taking different levels of coenzyme Q10, four times a day. The doses ranged from 300 mg/day to 1,200 mg/day. All the participants also took vitamin E. They were followed for 16 months, or until the investigator determined that the patient needed levodopa.

Side effects of coenzyme Q10 were mild, and no patient required a lowering of dose. Side effects were not more pronounced with the dietary supplement than with placebo. The patients were evaluated with the Unified Parkinson Disease Rating Scale (UPDRS). A slowing of the progression of the disease was evident in all three groups taking coenzyme Q10, and it was greatest in the group receiving the highest dose.

Dr. Beal, who is also Neurologist-in-Chief at NewYork-Presbyterian Hospital Weill Cornell Medical Center, said that he and his co-investigators are now planning a larger, Phase III clinical trial, using both the 1,200 mg/day dose and possibly a higher dose of coenzyme Q10.

The other authors of the article are Clifford W. Shults and Richard Haas (University of California-San Diego, La Jolla); David Oakes, Karl Kleburtz, Ira Shoulson, Roger Kurlan, and Sandy Plumb (University of Rochester School of Medicine and Dentistry); Jorge L. Juncos and Ray L. Watts (Department of Neurology and Wesley Woods Center, Emory University); John Nutt and Julie Carter (Oregon Health and Science University); Katie Kompoliti (Rush Presbyterian/St. Luke's Medical Center, Chicago); Joel S. Perlmutter (Washington University, St. Louis); Stephen Reich (Johns Hopkins University); Matthew Stern (University of Pennsylvania and Parkinson's Disease Research, Education and Clinical Center-Veterans Affairs Medical Center, Philadelphia); Eric Molho (Albany Medical College); Madeline Harrison (University of Virginia); Mark Lew (University of Southern California); and the Parkinson Study Group.

The research was supported by the National Institute of Neurological Disorders and Stroke (NINDS).