Association between Anemia and Risk of Parkinson Disease

Abstract

Background and Objective. People with anemia have higher rates of developing Parkinson disease (PD) than the general population. Previous epidemiological studies have invested the risk of PD in patients with anemia. However, the findings are still inconclusive. Therefore, we did a systematic review with meta-analysis to clarify the association between anemia and risk of PD. Methods. We systematically searched articles on electronic databases such as PubMed, Embase, Scopus, and Google Scholar between January 1, 2000 and July 30, 2020. Articles were independently evaluated by two authors. We included observational studies (case-control and cohort) and calculated the risk ratios (RRs) for associated with anemia and PD. Heterogeneity among the studies was assessed using the $Q$ and $I^2$ statistic. We utilized the random-effect model to calculate the overall RR with 95% CI. Results. A total of 342 articles were identified in the initial searches, and 7 full-text articles were evaluated for eligibility. Three articles were further excluded for prespecified reasons including insufficient data and duplications, and 4 articles were included in our systematic review and meta-analysis. A random effect model meta-analysis of all 4 studies showed no increased risk of PD in patients with anemia ( $N=4$ , $\text{R}{\text{R}}_{\text{adjusted}}=1.17$ (95% CI: 0.94-1.45, $p=0.15$ ). However, heterogeneity among the studies was significant ( $I^2=92.60$ , $p=<0.0001$ ). The pooled relative risk of PD in female patients with anemia was higher ( $N=3$ , $\text{R}{\text{R}}_{\text{adjusted}}=1.14$ (95% CI: 0.83-1.57, $p=0.40$ ) as compared to male patients with anemia ( $N=3$ , $\text{R}{\text{R}}_{\text{adjusted}}=1.09$ (95% CI: 0.83-1.42, $p=0.51$ ). Conclusion. This is the first meta-analysis that shows that anemia is associated with higher risk of PD when compared with patients without anemia. However, more studies are warranted to evaluate the risk of PD among patients with anemia.