Scientists found people who had studied for nine years or longer had the highest risk of developing Parkinson's, with physicians most at risk of contracting the debilitating condition. The researchers said it was possible that early Parkinson's triggered a desire to spend a lot of time studying, rather than long periods of education increasing susceptibility to the condition.

However, they said further study was needed to explain the link between education and the disease and warned that, while the findings reflected an association between a long academic career and Parkinson's, this did not necessarily mean a causal connection.

Parkinson's is a chronic, degenerative motor system disorder that causes devastating co-ordination problems and tremors. The cause of the disease is unknown, although it has been linked to genetic and environmental factors. The researchers, from the Mayo Clinic, in Olmsted County, Minnesota, examined the medical records of everyone in Olmsted County who developed Parkinson's from 1976 to 1995.

They found the highest levels of Parkinson's disease in people with nine or more years of education. The degree of risk was seen to rise with additional years of schooling.

Among a range of occupations, physicians were most at risk, while people in active, manual jobs, such as construction and factory workers, had the lowest risk.

No clear explanation for the trend has yet been found. But previous Parkinson's research has shown that regular exercise can protect against the disease, and, for those already affected, slow its onset. Researchers theorise the risk of Parkinson's may be higher in people with sedentary occupations.

Investigator Dr Roberta Frigerio said the findings should be interpreted with care, saying the influence of education and occupation "may be surrogates for a variety of exposures, physical activity, personality or socioeconomic status".

Fellow researcher Dr Demetrius Maraganore said: "I don't think that schooling or wearing a stethoscope causes brain cells to degenerate, or that digging holes with a digger protects your brain cells from atrophy, but I think that these are indirect indicators of factors that may relate to brain degeneration.

"What we now need to do is use these clues to try to identify those molecular-level events that differentiate these people."

He said it would be premature for anyone radically to alter their decision to study on the basis of the findings.

Yesterday, Britain's Parkinson's Disease Society warned against a "golden bullet" theory as to what causes the baffling condition.

A spokeswoman said: "The society welcomes research into the condition and we look forward to further work in this area."