People with Parkinson’s disease may have higher levels of selenium — a mineral with antioxidant properties — in their cerebrospinal fluid, the liquid that surrounds the brain and spinal cord, a study suggests.
The research, “Selenium level does not differ in blood but increased in cerebrospinal fluid in Parkinson’s disease: a meta-analysis,” was published in the International Journal of Neuroscience.
Although the exact trigger for Parkinson’s disease still remains to be identified, research indicates that its causative mechanism involves genetics, ageing, deficiencies in mitochondria — cells’ powerhouses — and oxidative stress.
Oxidative stress is an imbalance between the production of harmful free radicals — toxic molecules that are the natural byproducts of ongoing biochemical reactions in the body — and the ability of cells to detoxify. It results in cellular damage.
Such molecular and cellular changes eventually lead to the progressive death of dopamine-producing neurons in Parkinson’s disease.
Selenium is a critical mineral that has antioxidant properties, is essential for brain health, and plays a role in immune functions as well as anti-cancer activity.
Despite its antioxidant properties, conflicting evidence exists in regard to the role selenium plays in Parkinson’s. Several studies have found higher selenium levels in people with the disease, compared with healthy individuals, but others have shown regular or decreased levels of selenium in this patient population.
Now, a team led by researchers at Zhengzhou University, in China, evaluated all available evidence regarding selenium levels in the blood and cerebrospinal fluid, known as CSF, in the context of Parkinson’s disease.
The investigators searched the records of three biomedical databases that included studies from 1995 up through October 2019, examining associations between selenium levels and Parkinson’s risk.
The team analyzed a total of 12 case-control studies, which involved 601 Parkinson’s patients (mean age 57.62 to 70 years) and 749 healthy people (controls).
Compared with the healthy controls, the Parkinson’s patients had significantly higher selenium levels in their cerebrospinal fluid, the results showed. No differences were found in blood selenium concentration between the two groups.
“We speculate that oxidative stress conferred by the pathogenesis [disease characteristics] of [Parkinson’s disease] can lead to higher selenium levels and increased antioxidant capacity as a protective mechanism,” the researchers said.
While the investigators said their “results are convincing,” they did report great disparity between the studies analyzed. Such heterogeneity could be due to several factors, the researchers said, including the distinct methods by which the studies selected participants and quantified selenium levels, and inadequate matching between patients and healthy controls in each study. In addition, some of the studies lacked an analysis that minimized potential confounding factors like age, gender ratio, treatment, and the presence of other diseases — all of which might affect selenium levels in the body, the researchers said. Moreover, the analyzed studies were carried out in dozens of countries.
In these types of meta-analyses, when researchers combine the results of multiple scientific studies, there is always the possibility of publication biases, the investigators noted. Such publication bias can occur because studies with significant, or positive, findings are more likely to be published than studies with negative findings. This means that any meta-analysis or literature reviews based on published data could potentially be biased as a result.
In this case, however, the team used a specific statistical test — called a Begg’s test — to assess for this type of asymmetry of data and found no significant publication bias.
The researchers concluded that Parkinson’s patients may have higher selenium levels in their cerebrospinal fluid. However, further study is necessary as this finding, although significant, was associated with great data heterogeneity, they said.