medwireNews: Regularly taking high-dose vitamin B6 and B12 supplements over a 10-year period is associated with a significantly increased risk for lung cancer, particularly in men who smoke, study findings indicate.
By contrast, women and people who consumed B vitamins from multivitamin sources had no increased risk, and there was also no link between folate intake and the development of lung cancer, Chi-Ling Chen (National Taiwan University, Taipei) and co-authors report in the Journal of Clinical Oncology.
The findings are based on a study of 77,118 men and women, aged 50 to 76 years, who were members of the Vitamins and Lifestyle (VITAL) cohort, which was specifically designed to investigate long-term supplement use in relation to cancer risk.
During a mean 6 years of follow-up, there were 808 cases of incident invasive lung cancer.
The researchers found that men who used vitamin B6 and B12 individual supplements at least once per week for at least 1 year in the 10 years before baseline had significant 40% and 33% increased risks for lung cancer, respectively, compared with nonusers.
When the researchers assessed the 10-year average daily supplement dose, they found that the increased lung cancer risk was only significant among those with the highest intake of vitamin B6 (>20 mg/day) and B12 (>55 µg/day), at hazard ratios of 1.82 and 1.98, respectively, compared with nonusers.
However, the greatest risk occurred among men who were smokers at baseline; those with the highest intake of vitamin B6 and B12 had significant 2.93 and 3.71-fold increased risks for lung cancer, respectively, compared with nonusers.
Of note, the lung cancer risk was attenuated among both recent (less than 10 years since quitting) and former (10 or more years since quitting) smokers.
Chen and team also found that high-dose vitamin B6 and B12 use increased the risk for all lung cancer histologic types, with the exception of adenocarcinoma, which they say “is the type less related to smoking.”
The researchers explain that several B vitamins interact with homocysteine and methionine in the one-carbon metabolism pathway, which is “considered important for DNA integrity maintenance and gene expression regulation.”
“[D]isruption of this process may promote carcinogenesis,” they add, suggesting that the effect may be more pronounced in men, as observed in this study, because “androgen signaling regulates key enzymes involved in the one-carbon metabolism pathways.”
In addition, “[m]en and women have different susceptibility to tobacco-induced lung cancer and supplementation with high-dose vitamins B6 and B12 for longer duration may support more rapid cell growth and promote carcinogenesis in already mutated cells in smoking men,” they hypothesize.
Chen et al conclude that their findings “provide evidence that high-dose B6 and B12 supplements should not be taken for lung cancer prevention and, in fact, may increase risk of this disease in men.”
By Laura Cowen
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