Vitamin B6, also known as pyridoxine or pyridoxal phosphate, is an important component of folate metabolism. B6 is part of the pathway that produces a supply of methionine to serve as a main donor for active methyl groups and components for DNA synthesis and repair.
It is hypothesized that the deficit or surplus of vitamin B6, as well as other B vitamins, may play a role in carcinogenesis and may therefore be a target for chemoprevention or antitumor activity.1
Multiple studies evaluated the role of vitamin B6 in cancer risk and its efficacy as an antitumor or anti-toxicity agent.
Modulation of Cancer Risk
A large, prospective study of 27,853 women aged 45 or older evaluated the role of dietary components, including B vitamins, and risk of breast cancer with a median follow-up of 4.2 years.
Vitamin B6 intake overall (hazard ratio [HR], 0.67; 95% CI: 0.50-0.91; Ptrend = .01), through the diet (HR, 0.74; 95% CI: 0.44-0.99; Ptrend = .04), and by supplementation (HR, 0.61; 95% CI: 0.38-0.98; Ptrend = .05) were significantly associated with a decreased risk of breast cancer.2
Higher serum levels of vitamin B6 — even after adjustment for levels of folate, vitamin B12, and homocysteine — were associated with lower risk of non–small cell lung cancer (NSCLC) among 600 older men in a case-control study (odds ratio [OR] lowest vs highest quintiles, 0.51; 95% CI: 0.23-0.93; Ptrend = .02).3
Greater dietary intake of vitamin B6 (relative risk [RR], 0.69; 95% CI: 0.41-1.15), but not supplementation, was associated with a decreased risk of colorectal adenocarcinoma (CRC) in a nested case-control study of 37,916 women aged at least 45 with a mean 10.1-year follow-up.4
A randomized trial evaluating folic acid supplementation also found a trend toward association between higher vitamin B6 plasma levels and lower risk of CRC (RR lowest vs highest quintiles, 0.78; 95% CI: 0.61-1.00; Ptrend = .08).5
Yet in a double-blind, placebo-controlled trial of 1470 women from the Women’s Antioxidant and Folic Acid Cardiovascular Study, there was no effect on CRC risk with combined supplementation with folic acid (2.5 mg), vitamin B6 (50 mg), and vitamin B12 (1 mg).6 A cohort of 379 women aged at least 42 from the same study demonstrated no difference in risk of developing invasive or breast cancer with combined supplementation compared with placebo.7
A randomized trial of patients with stroke or transient ischemic attack demonstrated no difference in B vitamins supplementation or placebo for cancer incidence or for cancer mortality.8