"B Vitamin Intake and the Risk of Colorectal Cancer Development: A Systematic Review and Meta-Analysis of Observational Studies"

Methylenetetrahydrofolate Reductase; Newcastle-Ottawa Preferred Reporting for Systematic Reviews and Meta-Analyses; Quality of Life; Relative S-Adenosyl-homocysteine; S-Adenosylmethio-nine; Background: Cancer research has increased interest in lifestyle factors. These can affect colorectal cancer burden, which is the second common cause of cancer death worldwide, although 40% of the cases would be preventable. Aim: We aimed to conduct a systematic review and meta-analysis on relationship between B vitamin intake and colorectal cancer where 14 publications were analysed. Methods: We carried out a systematic search of scientific literature based on PRISMA statements. Combined effect size (CES), confident interval (CI), prediction interval (PI), I2 and publication bias were calculated during statistical analysis of selected studies. Results: Combined effect sizes showed inverse association between higher intake of vitamin B2 (CES = 0.90; CI95% 0.83 - 0.97; I2 = 0.00%, p = 0.910), B6 (CES = 0.80; CI95% 0.68-0.92; I2 = 9.17%, p = 0.359) and CRC. We could not confirm the higher dietary intake of vitamin B12 reducing the risk of CRC. Vitamin B2 and B6 could compensate the effect of MTHFR C677T polymorphism (CES = 0.81; CI95% 0.64 - 0.98; I2 = 0.00%, p = 0.515) as well. Conclusion: Our results suggest that optimal intake of vitamin B2 and B6 could be important dietary factors in prevention of CRC. The association with vitamin B12 is inconsistent as its bioavailability is affected by other lifestyle factors. Vitamin B2 and B6 could influence MTHFR enzyme activity, therefore these vitamins might be incorporated into screening process of CRC with recommendations for specific diet.