Research suggesting a possible link between the statin heart drugs being taken by millions of people and Parkinson’s disease has prompted scientists to launch an investigation involving tens of thousands of patients.

Researchers in the United States have been sufficiently alarmed by the preliminary findings of a small study of 124 patients to plan a full trial with 16,000 participants to examine whether the world’s best-selling drugs can heighten the risk of developing the condition.

While previous work has suggested that taking statins, which lower levels of LDL or “bad” cholesterol, might be a risk factor for Parkinson’s, there has never been firm evidence of a link, and previous efforts to test it have failed to find one. A study at the University of North Carolina, however, has shown that patients with low levels of LDL cholesterol are more than three and a half times as likely to develop the disease as those with higher LDL levels. Xuemei Huang, who led the research, said that she was very concerned by the finding.

Another large-scale trial investigating a cholesterol link with Parkinson’s risk is under way at Harvard University.

Millions of people around the world are taking statins. They have relatively few serious side effects, and there is evidence that they reduce deaths from heart disease.

They are considered to be so safe that one, simvastatin, is available without prescription in Britain.

David Dexter, senior lecturer in neuropharmacology at Imperial College, London, said: “With the evidence we have at the moment, I would say there is not much cause for concern that statin use may cause Parkinson’s disease. Previous studies have demonstrated that statins can increase brain dopamine concentration, the chemical transmitter deficient in Parkinson’s.

“Also one of the secondary symptoms some patients with Parkinson's experience is dementia, similar to Alzheimer’s disease, which may result from vascular changes in the brain. Statins would be expected to protect the brain against such vascular changes.”

The apparent link found between lower LDL levels and Parkinson’s was worrying, he acknowledged, but the study had been carried out on a small number of subjects and needed confirming. “Lower LDL cholesterol levels may also be a consequence of Parkinson’s and not a cause,” he said.

Patricia Limousin, consultant neurologist at the Institute of Neurology in London, said: “There is absolutely no evidence that statin drugs cause Parkinson’s disease. In fact these drugs were related to a lower occurrence of Parkinson’s disease in Huang’s study, raising the possibility of a protective effect that warrants further investigations.”

Peter Weissberg, medical director of the British Heart Foundation, said: “We are concerned that any suggestion of a link between statins and Parkinson’s disease would unnecessarily scare the millions of people benefiting from statins in the UK. There is overwhelming evidence that statins save lives by preventing heart attacks and strokes.

“Nobody should stop taking statins on the basis of this report. If they do, they will be putting themselves at increased risk of heart attack or stroke.”

Kieran Breen, director of research and development for the Parkinson’s Disease Society, said: “We should wary of drawing any firm conclusions from this research.”