Association of anemia with Parkinson’s disease: a systematic review with meta-analysis of epidemiological studies

Abstract Background: As more risk factors are identified for Parkinson’s disease (PD), attention has increased toward hematological disorders, as studies have found increased eryptosis, a process characterized by increased erythrocyte apoptosis, in PD patients. We aimed to synthesize scientific evidence assessing the effect of anemia on future PD incidence. Material and methods: A systematic review was conducted on multiple electronic databases. Any study that assessed the effect or association between presence of anemia and future PD in a longitudinal manner was considered for inclusion. Results: Five of the 5525 articles met inclusion criteria; three retrospective cohort studies and two case–control studies. Anemia exposure definition varied among studies. Four of the five studies observed an increased risk for PD; pooled analysis showed a non-significantly increased risk for PD in the cohorts (RR = 1.10; 95% CI = 0.08-15.84) and case–control studies (RR = 1.44; 95% CI = 0.04-52.47). However, heterogeneity among studies was high (I2 = 97, p < 0.01 and I2 = 85, p < 0.01, respectively). Conclusion: There are few clinical studies on the association of anemia and PD, despite growing preclinical evidence on their connection. In this review, a tendency toward an increased risk for PD in anemic population was observed, with further research needed to reach a definite conclusion.