[...]But when the Swedish team compared blood levels of these factors to prostate cancer risk in a prospective study of 254 men with prostate cancer and 514 matched men without known prostate cancer, they found something odd and surprising.
Folate and B12 were expected to be protective against prostate cancer, because folate, vitamin B12 and homocysteine are essential for methyl group metabolism and thus also for DNA methylation. Abnormal methylation, primarily hypermethylation of certain genes including tumor suppressors, has been implicated in prostate cancer development.
But in fact, increasing plasma levels of folate and vitamin B12 were statistically significantly associated with increased prostate cancer risk, with an odds ratio of 1.60 for folate and 2.63 for vitamin B12 for highest vs. lowest quartile.
Increasing plasma homocysteine levels were associated with a reduced risk of borderline significance.
After adjustment for body mass index and smoking, a statistically significant increased risk remained only for vitamin B12.
The researchers say: "Our results suggest that factors contributing to folate status are not protective against prostate cancer. On the contrary, vitamin B12, associated with an up to 3-fold increase in risk, and possibly also folate, may even stimulate prostate cancer development. These findings are novel and should be explored further in future studies."