Dietary Antioxidants and the Risk of Parkinson’s Disease: A Systematic Review and Dose-Response Meta-Analysis of Observational Studies

• Main Author: talebi, sepide
• Format: Text
• Language: unknown
• Published: Open Science Framework 2022
• Subjects: Medicine and Health Sciences; Greenland; Laird
• Online Access: https://dx.doi.org/10.17605/osf.io/kpsm9; https://osf.io/kpsm9/

Review question: Is there any association between dietary intake of various antioxidants and the risk of Parkinson’s disease? Searches: The systematic search was conducted in major databases including PubMed, Web of Science, and Scopus until 5 March 2021, with no restrictions in publication time or language. Types of study to be included: Observational studies such as case-control, nested case-control, and cohort studies. Condition or domain being studied: Parkinson’s disease is a progressive neurodegenerative disorder characterized by rigidity, slowness of movement, and tremor. Recent evidence suggests that oxidative stress and high levels of reactive oxygen species play an important role in the pathogenesis of this disease. Regarding the evidence, it seems that dietary antioxidants are known as neuroprotective agents in Parkinson's disease. However, data on the associations between dietary intake of antioxidants and the risk of Parkinson’s disease are conflicting. Hence, we will conduct a systematic review and meta-analysis of observational studies to evaluate the association between dietary intake of various antioxidants and the risk of Parkinson’s disease. Participants/population: adults aged ≥18 year Intervention(s), exposure(s): Observational studies that reported the consumption of dietary antioxidants (e.g. vitamin C, vitamin E, vitamin A, selenium, zinc, α-carotene, β-carotene, lycopene, β-cryptoxanthin, lutein, and flavonoids) as exposure. Comparator(s)/control: subjects in the lowest categories of dietary intake of the following antioxidants: vitamin C, vitamin E, vitamin A, selenium, zinc, α-carotene, β-carotene, lycopene, β-cryptoxanthin, lutein, and flavonoids. Main outcome(s: The incidence rate of Parkinson’s disease Data extraction (selection and coding): The following population characteristics from each eligible study will be extracted by two independent reviewers: first author’s name, year of publication, country, study design, duration of follow-up, instruments used to assess antioxidant intake, sample size, confounders adjusted, and comparison categories and relevant effect sizes (RR, HR, OR) along with 95% confidence interval. Risk of bias (quality) assessment: The Cochrane Risk of Bias in Non-randomized Studies of Interventions (ROBINS-I) tool and Grading of Recommendations Assessment, Development and Evaluations (GRADE) will be used to assess the methodological quality of studies. The process of quality assessment will be conducted by two independent authors. Any disagreement will be solved by a third reviewer. Strategy for data synthesis: We will calculate a meta-analysis to summary RR and 95% CIs for the association between antioxidant intake and subsequent Parkinson risk. If studies have reported HR as an effect size, we consider it as RR. when OR was reported, we will convert it to RR with the available formulas. For the highest vs. lowest category analysis, we will carry out a pairwise meta-analysis to pool the reported risk estimates using the DerSimonian and Laird random-effects. In each meta-analysis, subgroup analysis will distinguish between case-control and cohort studies. Heterogeneity among the studies was assessed by using Cochran's Q test and I2 statistics. We will run a subgroup analysis to explore the source of heterogeneity. Moreover, Egger’s regression test and Begg’s test method will evaluate the possibility of publication bias. We will also perform sensitivity analyses to check the robustness of the overall effect by excluding each study. Eventually, to dose-response meta-analysis, we will compute from the natural logs of the RRs and CIs across categories of dietary intake of various antioxidants and risk of Parkinson’s disease according to Greenland and colleague’s methods. All statistical tests will be conducted using STATA version 14.0.