Coenzyme Q10 was given to 80 Parkinson's patients - and while not everyone benefited, in some the disease slowed by up to 44%.

The drug is now being tested over a longer period with a larger group of patients to confirm this result.

Parkinson's disease affects approximately 1% of people over the age of 65.

While certain medications can reduce the symptoms of Parkinson's, they do not slow the progressive deterioration in function, which the study suggests can be achieved with coenzyme Q10

Robert Meadowcroft, Parkinson's Disease Society

It is a degenerative disorder in which patients develop tremor and muscle stiffness because they have too little dopamine - a brain chemical.

Until now, drugs such as levodopa have concentrating on supplementing the amount of dopamine available day by day - but the disease still gets progressively worse.

If successful, Q10, or a drug like it, could be the first to actually hold back the advance of the disease.

Four doses

The 80 patients on the trial, in the US, all had early Parkinson's disease, and although they had some symptoms, they did not yet need levadopa.

They were given Q10 four times daily at a variety of doses.

Doctors then waited to see how the physical symptoms of their disease progressed.

By the eight month mark, there was a clear pattern, with those on the highest dose of Q10 faring much better than those given a "placebo" sugar pill.

Even those on lower doses of Q10 were better able to carry out simple "daily living" activities such as washing or dressing, and had better mental function and mood.

Lead researcher Professor Clifford Shults, from the University of California in San Diego, said: "While it is tremendously encouraging that our results indicate that it is likely that coenzyme Q10 slows the progression of Parkinson's disease, our study did not have sufficient numbers of patients to unequivocally prove that it does."

He said it would be "premature" to recommend that Parkinson's patients took the supplement.

Cell 'powerhouse'

Q10 appears to play a key role in the function of mitochondriae - cell components which are responsible for turning nutrients into energy.

Previous research has suggested that mitochondrial function is impaired in Parkinson's patients - and that Q10 appears to be lacking in their mitochondriae.

A spokesman for the Parkinson's Disease Society in the UK also described the finding as "encouraging".

Robert Meadowcroft,its director of policy, research and information, said: "Parkinson's disease is a condition whose cause is described as multifactorial.

"It is generally regarded in most cases as resulting from a combination of a genetic susceptibility and an environmental trigger.

"While certain medications can reduce the symptoms of Parkinson's, they do not slow the progressive deterioration in function, which the study suggests can be achieved with coenzyme Q10."

However, he said that further research was needed to back up the results.

The research was published in the journal Archives of Neurology.