Thousands of people across the United States are diagnosed with Parkinson's disease every year. New research examines the effect of statins on the risk of developing this neurodegenerative disease.
Every year, approximately 50,000 people in the U.S. are diagnosed with Parkinson's disease. The National Institutes of Health (NIH) estimate that half a million people in the country live with the illness.
Statins are a type of drug commonly used to decrease "bad" cholesterol levels in the blood. Often prescribed to patients at risk of cardiovascular disease, statins improve the blood flow and restore the elasticity of the arteries.
Recently, there has been an increasing interest in the potential of statins to protect brain cells and thus prevent the onset of neurodegenerative diseases such as Parkinson's and Alzheimer's disease.
Xuemei Huang, Ph.D. - a professor of neurology at Penn State College of Medicine in Hershey, PA, and an author of the new study - describes another reason why the evidence of the neuroprotective role of statins has been inconclusive so far:
"Higher cholesterol," Prof. Huang says, "the main indication to use statins, has been related to lower occurrence of Parkinson's disease. This made it hard to know if the statin['s] protective effect was due to the drug or preexisting cholesterol status." But the new research Prof. Huang carried out with her colleagues accounts for this factor.
Co-author Guodong Liu, Ph.D., an assistant professor of public health sciences, explains, "A diagnosis of hyperlipidemia, a marker of high cholesterol, was associated with lower Parkinson's disease prevalence, consistent with prior research. We made sure to account for this factor in our analysis."
The new findings were published in the journal Movement Disorders.
Fat-soluble statins may increase risk of Parkinson's disease
The team examined medical insurance claim data from 50 million people. Of these, they selected 22,000 people living with Parkinson's disease, 2,322 of whom were newly diagnosed with the disease.
The researchers also selected a control group of people who did not have Parkinson's. They then identified the patients who had been taking statins and determined the length of use before their first Parkinson's symptoms appeared.
The study found that the use of statins correlated with a higher risk of developing Parkinson's disease. This effect was stronger at the beginning of the statin treatment, or more specifically, for statin use of under 2.5 years.
Additionally, the association was stronger for so-called lipophilic statins. Most statins are lipophilic, and they include atorvastatin, fluvastatin, lovastatin, cerivastatin, pitavastatin, and simvastatin. They are called lipophilic because they diffuse in lipids, whereas hydrophilic statins diffuse in water.
The former can distribute more widely in various tissues, as they enter the cells more easily. Lipophilic, or "fat soluble," statins can also reach the brain, whereas water soluble ones cannot.
Prof. Huang points out that the findings contradict previous beliefs that lipophilic statins may have a neuroprotective effect.
"Statin use was associated with higher, not lower, Parkinson's disease risk, and the association was more noticeable for lipophilic statins, an observation inconsistent with the current hypothesis that these statins protect nerve cells," she says.
Finally, Prof. Huang points to previous research that suggested that stopping treatment with statins may lead to Parkinson's disease. Instead, based on the findings of the new study, she suggests that it might be the case that the "use of statins may lead to new Parkinson's disease-related symptoms, thus causing patients to stop using statins."
Although more studies are needed to better understand these results, Prof. Huang advocates for a cautious use of statins, particularly for those patients at higher risk of developing Parkinson's disease.
"We are not saying that statins cause Parkinson's disease, but rather that [...] statins should not be used based on the idea that they will protect against Parkinson's. People have individual levels of risk for heart problems or Parkinson's disease."