Updated on February 8, 2023
For patients with Parkinson’s disease, one of the most challenging aspects is uncertainty. Because the progress of the disease differs significantly between patients, it is difficult to predict the timing of the stages and the severity of the symptoms. Moreover, patients and practitioners contend with the fact that the existing pharmacological therapies are insufficient for addressing all concerns: they vary in their effectiveness for individual patients, and most of them only offer relief for the motor symptoms of Parkinson’s disease. That leaves a wide range of non-motor symptoms untreated, including sleep problems, cognitive impairment, sialorrhea, and hypotension. Traditional pharmacological therapies also often have side effects that interfere with a patient’s quality of life. Because of these issues, more scientists are looking to nutritional factors that might aid in the effective management of Parkinson’s disease. One of the nutritional support supplements for Parkinson’s that has emerged as a viable possibility is quercetin.
Quercetin is plant pigment commonly found in vegetables, fruits, flowers, and herbs. As a flavonoid, it is well-recognized for its antioxidant effects and ability to support the body’s natural inflammatory response. Quercetin continues to draw the attention of the research community as more studies establish connections between antioxidant supplements and their neuroprotective attributes. Although clinical trials are still lacking, there have been several promising in vitro and animal model studies, which cumulatively suggest there are multiple mechanisms through which a quercetin supplement might benefit Parkinson’s disease patients.
One of the early animal studies indicating that a quercetin supplement could benefit Parkinson’s disease patients was published in the journal Neuroscience Letters in 2011. The researchers wanted to know whether taking quercetin might have an effect on dopamine levels in rat models of Parkinson’s disease, based on the fact that one of the most effective pharmacological therapies for Parkinson’s disease is levodopa—a chemical precursor to dopamine combats declining levels of dopamine, which interferes with the patient’s ability to control their body movements and contributes to a variety of non-motor symptoms. After 14 days of receiving quercetin, the levels of quercetin in the rat models had increased significantly, along with the levels of enzymes involved in key antioxidant processes that could provide neuroprotection. Importantly, these observations were also associated with better neuron survival in the rats. Thus, the researchers concluded that taking quercetin could aid in both the reduction of oxidative damage and neuronal loss associated with Parkinson’s disease.
More recently, in 2016, a group of scientists from Tanta University in Egypt conducted an animal model study that established a link between quercetin and another neurochemical pathway associated with Parkinson’s disease: autophagy. Autophagy refers to the cell’s metabolism of its own tissues. In scientific circles, although this cellular process is traditionally associated with starvation, scientists are increasingly recognizing its importance for neuronal homeostasis. Autophagy removes damaged organelles and aggregated proteins in brain cells that contribute to neurodegeneration, and it can even contribute to oxidative processes that stress the endoplasmic reticulum (a key cell organelle) to the point where a cell undergoes apoptosis (programmed cell death). Thus, nutritional support supplements for Parkinson’s that combat dysfunctional autophagy could potentially provide benefits with regard to disease onset and progress.
To explore the possibility that quercetin could play such a role, the researchers treated rat models of Parkinson’s disease with quercetin for four weeks. After the trial period, the researchers used DNA fragmentation to examine changes in gene expression, and they used histopathological analysis to assess observable changes in rat tissue. Like the researchers who conducted the 2011 study, they found that quercetin supplementation resulted in higher levels of dopamine and antioxidant enzymes. In addition, they observed increases in the levels of several key autophagy-associated proteins, including Beclin-1 and C/EBP homologous protein (CHOP). Notably, they also reported significant declines in the behavioral impairments displayed by the rat models of Parkinson’s disease. Based on these results, the authors were able to draw three conclusions: that quercetin could enhance the functioning of the autophagy pathway, that it could lower the risk of ER stress-induced apoptosis by acting as an antioxidant, and that it could benefit several of the known symptoms of Parkinson’s disease.
Quercetin is not the only compound that has been proposed as a possible alternative therapy for Parkinson’s disease. Over the last decade, a combination of epidemiological studies and preclinical studies have associated coffee consumption with a lower risk of neurodegenerative diseases, including Parkinson’s disease. While that’s great news for coffee drinkers, scientists and supplement developers are more interested in determining the specific component of coffee that provides neuroprotection. Many scientists point to caffeine, suggesting the compound aids in the management of several the motor symptoms of Parkinson’s disease due to its effects on dopaminergic pathways. Indeed, caffeine can play a role similar to that of certain traditional pharmacological therapies that treat certain motor symptoms of Parkinson’s disease. However, many of these studies fail to explain the associations between coffee-drinking and the effects of caffeine on the non-motor symptoms of Parkinson’s disease.
In 2016, a group of researchers from the Kinsmen Laboratory of Neurological Research at The University of British Columbia proposed an alternative to the caffeine hypothesis: that it is quercetin in the coffee, not caffeine, that is reducing the risk for Parkinson’s disease. To explore this idea, the researchers examined how a number of different coffee components—including quercetin, caffeine, flavones, and chlorogenic acid—affected cell models of neurodegenerative disease.Through a series of in vitro studies, they determined that quercetin could limit neurotoxicity by restricting the damage to DNA, lipids, and proteins. This results in a rise in glutathione, a key compound known to protect against oxidative damage in Parkinson’s disease. Although caffeine did provide minor benefits, they were minimal compared to the significant impacts of quercetin. Thus, the researchers concluded that it is quercetin—not caffeine—that is the major neuroprotective component in coffee.
For patients and practitioners, there’s no denying that studying quercetin as a nutritional support supplement for Parkinson’s patients is still in its infancy. However, given that traditional pharmacological therapies are not effective for all patients—and generally fail to address non-motor symptoms—utilizing quercetin as a supplement in a highly bioavailable form could be a viable strategy. The evidence supporting its efficacy in the lab is strong, and it will be exciting to see how these results translate to clinical studies in the future.
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