Excessive vitamin B6 during treatment is related to poor prognosis of patients with nasopharyngeal carcinoma: A U-shaped distribution suggests low dose supplement

Summary Background & aim Several studies explored the association of vitamin B6 intake with the risk of cancers. However, it is unclear whether different doses of vitamin B6 have distinct effects on the prognosis of nasopharyngeal carcinoma (NPC) patients. This study investigated the relationship between different doses of B6 intake and the prognosis of NPC patients. Methods This retrospective cohort analysis included 792 newly diagnosed NPC patients with a median follow-up of 62.05 months. Restricted cubic spline and maximally selected rank statistics were performed to determine the cut-off value of vitamin B6 during treatment (VB6DT). Kaplan–Meier method and log-rank tests were performed to analyze survival outcomes. A multivariable Cox proportional hazard model was performed to determine the independent prognostic factors. Results NPC patients were divided into three groups according to the cut-off value of VB6DT: non-users (0 mg/d), VB6DT > 8.6 mg/d, and VB6DT ≤ 8.6 mg/d. Patients with VB6DT > 8.6 mg/d had significantly lower 5-year overall survival (OS) (83.5% vs. 90.8%, p = 0.006), distant metastasis-free survival (DMFS) (83.5% vs. 91.0%, p = 0.004), and progression-free survival (PFS) (73.7% vs. 81.7%, p = 0.011) and slightly but not significantly lower 5-year local recurrence-free survival (LRFS) (87.7% vs. 90.7%, p = 0.214) than the non-users. Patients with VB6DT ≤ 8.6 mg/d had slightly but not significantly better 5-year OS (93.3% vs. 90.8%, p = 0.283) than the non-users, while all other primary endpoints were similar (p > 0.50). Multivariable analyses confirmed that VB6DT > 8.6 mg/d was an independent negative prognostic factor of OS (p = 0.010), DMFS (p = 0.017), and PFS (p = 0.030) but not of LRFS (p = 0.428). Conclusions Excessive VB6DT higher than the cut-off value is an independent negative prognostic factor for NPC patients. Additionally, low dose intake improved OS only slightly but not significantly.