A new study has shown that taking high-dose vitamin B supplements over a long period is associated with an increased risk of lung cancer among men.
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The study, which analysed data for 77,000 people, showed that long-term use of the supplements increased the cancer risk among men by between two and four times, compared with non-use. No such effect was observed for women.
This risk was further increased among male smokers who took more than 20 mg of B6 or 55 mg of B12 every day for ten years. Taking B6 at this dose increased the lung cancer risk by three times and taking B12 at this dose increased it by four times.
Taking these supplements has previously been shown to have a protective effect against lung cancer, but the authors of the current study say this appears to be a double-edged sword.
“Consistent with prior evidence of harm for other vitamin supplements on lung cancer risk in male smokers, the associations we observed provides evidence that high-dose B6 and B12 supplements should not be taken for lung cancer prevention and may, in fact, increase the risk of this disease in men,” they write in the Journal of Clinical Oncology.
For the study, epidemiologists Theodore Brasky (The Ohio State University Comprehensive Cancer Center, Columbia) and colleagues analysed data from the VITamins And Lifestyle (VITAL) cohort study, which was designed to assess the use of vitamin and mineral supplements in relation to cancer risk.
The participants (aged 50 to 76), who were recruited between 2000 and 2002, provided information on their use of vitamin B over the previous ten years, including details about dosage. The researchers used statistical techniques to adjust for a host of factors including age, race, smoking history, education, alcohol consumption, body size, use of anti-inflammatory drugs, personal history of cancer or lung disease and family history of lung cancer.
This sets all of these other influencing factors as equal, so we are left with a less confounded effect of long-term B6 and B12 super-supplementation,"
Theodore Brasky, The Ohio State University Comprehensive Cancer Center, Columbia
"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. This is certainly a concern worthy of further evaluation."
Brasky and team are now conducting two more studies, one to see whether the results are repeated in another similarly large, prospective study of men and the other to examine the association among post-menopausal women, to confirm the current finding that women are not at any increased risk.