A Meta-analysis of Prospective Studies

PY R I D O X A L 5 -P H O S P H A T E (PLP), the principal active coenzyme form of vitamin B6, is involved in almost 100 enzymatic reactions. One function of vitamin B6 is its role in the 1-carbon metabolic pathway, which involves the transfer of 1-carbon groups for DNA synthesis and DNA methylation. Deficiency of vitamin B6 has been associated with considerably impaired 1-carbon metabolism in animals. Hence, low vitamin B6 levels may increase colorectal cancer risk through aberrations in DNA synthesis, repair, and methylation. Vitamin B6 may also suppress colorectal carcinogenesis by reducing cell proliferation, angiogenesis, oxidative stress, inflammation, and nitric oxide synthesis. Major food sources of vitamin B6 include fortified cereals, meat, fish, poultry, starchy vegetables, and some fruits (eg, bananas and avocado). Findings from prospective studies that have examined the association between vitamin B6 intake or PLP levels in the blood and the risk of colorectal cancer have been inconsistent. The aim of this review was to evaluate the evidence from prospective studies on vitamin B6 intake or blood levels of PLP and the risk of colorectal cancer by summarizing it quantitatively with a meta-analytic approach.