Does Caffeine Consumption Affect the Symptoms of Parkinson’s Disease? A Systematic Review of Clinical Trials

Objectives: This systematic review of the literature was carried out to see whether coffee consumption could affect Parkinson’s disease (PD) symptoms. Methods: Randomized controlled trials (RCTs), crossover studies, and quasi-experimental studies were assessed to evaluate the effect of caffeine on PD. The databases including Medline/PubMed, ProQuest, Embase, Cochrane Library, and ClinicalTrials.gov were systematically searched. The Cochrane Collaboration’s tool for assessing the risk of bias in randomized clinical trials and the Cochrane risk of bias assessment tool for non-randomized studies of interventions (ROBINS-I) were used to assess the quality of RCTs and non-randomized clinical trials, respectively. A meta-analysis of the results was not possible because of reporting different outcomes. Results: Four papers were included in this study. Only one study reported the significant effect of caffeine on ESS and UPDRS. Another study observed no significant effect of caffeine on ESS during three- and six-week interventions. However, a significant reduction in ESS scores in the sixth week was reported after excluding four protocol violations. This study reported that the UPDRS score reduced in the third week, but significant changes were observed after six weeks. The other two studies did not show a significant effect of caffeine on ESS and UPDRS. Conclusions: Since a meta-analysis was not conducted, there was insufficient evidence to evaluate the effect of caffeine on PD. Thus, it is recommended to conduct more well-designed RCTs with a larger sample size to assess the effect of caffeine on PD.