Previously, some studies have found that the cholesterol-lowering medications statins may offer protective benefits against Parkinson's disease. However, a new study led by researchers at Penn State College of Medicine and the National Institute of Environmental Health Sciences was unable to reproduce this association.
About 1 million people in the US are currently affected by Parkinson's disease. The causes of Parkinson's are unknown, but scientists know that damage to neurons that produce dopamine eventually results in the movement disorders characteristic of this neurodegenerative brain disease.
Xuemei Huang, professor of neurology and vice chair for research at Penn State College of Medicine, had found in previous research an association between high blood cholesterol levels and lower incidence of Parkinson's.
Despite Huang's findings being reproduced in some similar studies, evidence has been inconsistent. Some epidemiology studies had also reported an association between lowered Parkinson's incidence and use of statins, which lower levels of low-density lipoprotein (LDL) cholesterol.
However, whether or not statins were responsible for the lowered Parkinson's incidence was difficult to prove, as these studies did not account for cholesterol levels prior to the widespread use of statins in the US.
In the new study - published in the journal Movement Disorders - Huang attempted to test this association. To do this, his team looked at low blood cholesterol levels, medication history and Parkinson's symptoms among people who participated in the long-running Atherosclerosis Risk in Communities study.
From the analysis, the team confirmed its previous finding that high total cholesterol and LDL were associated with lower risk of Parkinson's.
Statins, however, did not appear to protect against the disease. What is more, the study found an increase in long-term risk of Parkinson's for users of statins.
Huang admits that the analysis of statin use and Parkinson's risk was based on a "fairly small number of cases," but argues that the preliminary data suggest statins do not protect against the disease.
Why did previous studies find that statins protect against Parkinson's disease?
Suggesting an explanation for why some studies have found statins to be protective against Parkinson's, Huang says:
"One possibility, is that statin use can be a marker of people who have high cholesterol, which itself may be associated with lower [Parkinson's] risk. This could explain why some studies have found an association between use of these medications and low incidence of [Parkinson's]. Most importantly, this purported benefit may not be seen over time."
More research is needed into the association between cholesterol and Parkinson's, Huang asserts. Increasingly, evidence is suggesting that Parkinson's may begin in areas outside of the brain, so decreases in blood cholesterol levels from statins may have unknown consequences in these regions.
Statins also reduce a compound called coenzyme Q10, which Huang believes should be investigated for Parkinson's associations in future studies. The compound produces energy for cells and is believed to have protective qualities in nerve cells.
"Statins have been proven to be effective in the primary and secondary prevention of cardiovascular events and stroke. Although some have proposed that statins might be a 'cure-all' drug," Huang says, "this might be a case where what's good for the heart isn't good for the brain."
"Statins have been very important for preventing and treating vascular disease, but we need more research to understand if in some cases there is collateral damage," he adds. He advises that until more research can further interpret the associations between Parkinson's, cholesterol and statins, scientists should remain cautious of promoting the benefits of statins for patients with Parkinson's disease.