Long-term use of high-dose vitamin B6 or B12 supplements may increase the risk of lung cancer in men, according to an analysis from the long-term observational VITAL study, which was designed to evaluate vitamin and mineral supplements in relation to cancer risk in 77,00 people (ages 50 to 76), published in the Journal of Clinical Oncology in August 2017. This risk was not seen in women.
The odds of developing lung cancer nearly doubled in men taking at least 20 milligrams of B6 (about 15 times the daily RDA) or 55 micrograms of B12 (about 22 times the RDA) for 10 years, compared to non-users—and tripled in male smokers who took such high doses.
Previous research has found similar increases in lung cancer risk in smokers taking high doses of beta carotene, but this is the first study to link this risk to these two B vitamins. High-dose B vitamins are sometimes promoted to boost energy or improve cognition, though there’s no good evidence for such claims.