High doses of coenzyme Q10, a dietary supplement often trumpeted as a preventer of heart disease, may slow the progress of Parkinson's for patients in the earliest stages of the disease, a study has found.

While the study offers little help for people such as Janet Reno and Michael J. Fox, who have long suffered from the disease, it may point to new research into how to stem the neurological degeneration associated with Parkinson's.

Still, researchers and local experts stopped short of advocating that everyone with Parkinson's rush to the health-food store to stock up on CoQ10.

''It's very encouraging that it may slow the progression of Parkinson's disease, but we haven't proven it yet,'' said Dr. Clifford Shults, principal investigator of the study, which he will present today at the American Neurological Association meeting in New York. The study appears in the Oct. 15 issue of Archives of Neurology.

Shults, a professor of neurosciences at the University of California at San Diego, said that 1,200 milligrams of CoQ10 a day reduced by 44 percent the deterioration in patients' ability to eat, dress, bathe and walk on their own. None of the patients had yet progressed enough to take levodopa, the drug commonly used to reduce symptoms.

With only 80 patients, however, the placebo-control study does not earn CoQ10 a definite spot in the anti-Parkinson's pharmacopeia, experts say.

''This is so preliminary, who knows if it works?'' said Dr. Joel Dokson, co-chief of neurology at Mount Sinai Medical Center in Miami Beach. ``To know if a drug really works, you need thousands of people on it.''

Future trials will include more patients and explore CoQ10's role in patients with more advanced disease, Shults said. Research also will explore how CoQ10 confers its beneficial effect. Investigators such as Shults have their suspicions.

A naturally occurring substance in the body, CoQ10 plays an integral role in the function of mitochrondria, which generate the energy that keeps cells going. Researchers noted that in the early stages of Parkinson's, the levels of CoQ10 in patients' mitochrondria had shrunk by a third.

Infusing patients with CoQ10, then, they reasoned, might help stave off the rapid decline characteristic of Parkinson's, a disease that strikes 50,000 new patients each year. This study suggests that researchers should look into restoring mitochondrial health to ease Parkinson's, Shults said.

''I think that this will just increase the attention that mitochondrial dysfunction is receiving,'' he said.

It also could increase the attention to CoQ10, an over-the-counter dietary supplement. Dr. Abraham Lieberman, medical director of the National Parkinson Foundation and a professor of neurology at the University of Miami, said the study's important to pass along to patients and let them make their own decisions.

''This may be very important, and it's your choice,'' Lieberman said he would tell patients, adding that the cost of CoQ10 -- about $150 a month -- might dissuade some. ``If I were you, I would probably go on it and spend the money.''

Researchers have long suspected that CoQ10, an antioxidant, and some of its cousins may help prevent other neurological disorders, such as multiple sclerosis and Alzheimer's, said Dr. Jeffrey Steinberg, medical director of Memorial Pembroke Hospital's Memory Disorder Center.

''[CoQ10] is a naturally occurring substance that you can probably take with impunity,'' said Allan Herskowitz, a neurologist on the staff of Baptist Hospital. ``If there's no downside from toxicity with this, there's no harm in trying it.''