There was an even greater link between B12 supplementation and lung cancer, too.
Current smokers who reported 10-year use of vitamin B6 at doses greater than 20 mg per day appeared almost three times as likely to develop lung cancer as nonusers (HR = 2.93; 95% CI, 1.5-5.72).
Compared with non-users, male smokers taking 55 microgram daily supplements of vitamin B12 for 10 years were four times more likely to develop the disease, a study found. "Our data shows that taking high doses of B6 and B12 over a very long period of time could contribute to lung cancer incidence rates in male smokers".
Editors note: This article has been corrected to reflect that lung cancer risk almost tripled and quadrupled in men who were current smokers and taking B6 and B12 at the highest levels compared to male smokers who did not take B6 or B12 supplements. Male smokers taking B6 at this dose were three times more likely to develop lung cancer.
"As far as the magnitude of the association, I think you could characterize our reaction as concerned; especially if you consider how common these supplements are". There also has been speculation that these vitamins may reduce cancer risk.
The recommended daily intake of B-12 is less than 2 micrograms and about 1 and 1/2 milligrams for vitamin B-6, according to researchers.
Why B vitamins influence cancer risk is not known for sure, but some believe that it is related to how B vitamins interact with the so-called one-carbon-metabolism pathway. The participants were from the Vitamins And Lifestyle cohort, which was set up to evaluate vitamin and mineral supplements and their relationship with cancer over the longer-term.
"That's marketing. That's not science", he said.
All participants enrolled in the state of Washington between 2000 and 2002, when they were aged 50 to 76. We were unable to address whether lung cancer patients had improved or worsened prognosis if they took these supplements.
Arthur G. James Cancer Hospital and Richard J. Solove Research Institute (OSUCCC - James), Fred Hutchinson Cancer Research Center and National Taiwan University report their findings in the August 22, 2017 issue of the Journal of Clinical Oncology. The authors of the new study said that the discrepancy could be because some of these studies measure B vitamins in the blood and not through dietary surveys, like they did. Results revealed that just over 800 of the study volunteers developed lung cancer over an average follow-up of six years.
Disclosures: The NCI, NIH and Office of Dietary Supplements funded this study.
In addition, the highest categories of supplementation reported in this study represent usage levels that can only be obtained from high-dose vitamin B supplements, Brasky said. The researchers report no relevant financial disclosures.