Gastrectomy, vitamin B12 supplementation and the risk of Parkinson's disease: A nationwide cohort study

Introduction: Previous evidence has suggested roles for α-synuclein propagation and vitamin B12 (VitB12) deficiency in the pathogenesis of Parkinson's disease (PD). We investigated whether gastric cancer (GC) patients who underwent gastrectomy had a lower risk of PD and whether VitB12 supplementation modified the risk. Methods: GC patients aged ≥50 years who underwent curative gastrectomy between 2007 and 2012 (n = 72,216) and matched comparison groups (n = 211,389) were identified from the Korean National Health Insurance database. The risks of PD were analyzed by Cox regression. Results: Compared to their matched comparison groups, GC patients who underwent gastrectomy showed a decreased risk of PD (adjusted HR [aHR] 0.86; 95% confidence interval [CI] 0.75–0.98), but the significance disappeared after further adjustment with smoking and body mass index (BMI). To elaborate, subtotal gastrectomy (STG) was associated with decreased risk of PD (aHR 0.85; 95% CI 0.74–0.99) while total gastrectomy (TG) was not (aHR 0.89; 95% CI 0.66–1.19), although the risk reduction was not significant when further adjusted for smoking and BMI. Among the patients who underwent TG, their risk of PD was markedly lower when they had VitB12 supplementation after surgery (aHR 0.36; 95% CI 0.17–0.76), while the risk was higher when they did not have any (aHR 1.55; 95% CI 1.03–2.32). Conclusions: GC patients who underwent gastrectomy and received uninterrupted VitB12 supplementation had a decreased incidence of PD. This study provides indirect epidemiological evidence for the potential roles of gastrectomy and VitB12 in the pathogenesis of PD.