A dose-response meta-analysis reveals an association between vitamin B12 and colorectal cancer risk.

Objective: The current meta-analysis evaluated the association between vitamin B12 intake and blood vitamin B12 level and colorectal cancer (CRC) risk.
Design: The PubMed and EMBASE databases were searched. A dose-response analysis was performed with generalized least squares regression, with the relative risk (RR) and 95 % CI as effect values.
Setting: The meta-analysis included seventeen studies.
Subjects: A total of 10 601 patients.
Results: The non-linear dose-response relationship between total vitamin B12 intake and CRC risk was insignificant (P=0·690), but the relationship between dietary vitamin B12 intake and CRC risk was significant (P<0·001). Every 4·5 μg/d increment in total and dietary vitamin B12 intake was inversely associated with CRC risk (total intake: RR=0·963; 95 % CI 0·928, 0·999; dietary intake: RR=0·914; 95 % CI 0·856, 0·977). The inverse association between vitamin B12 intake and CRC risk was also significant when vitamin B12 intake was over a dosage threshold, enhancing the non-linear relationship. The non-linear dose-response relationship between blood vitamin B12 level and CRC risk was insignificant (P=0·219). There was an insignificant association between every 150 pmol/l increment in blood vitamin B12 level and CRC risk (RR=1·023; 95 % CI 0·881, 1·187).
Conclusions: Our meta-analysis indicates that evidence supports the use of vitamin B12 for cancer prevention, especially among populations with high-dose vitamin B12 intake, and that the association between CRC risk and total vitamin B12 intake is stronger than between CRC risk and dietary vitamin B12 intake only.