If you are a smoker who takes individual supplements of Vitamins B6 or B12, it dramatically increases your risk of developing lung cancer.
This is not about multivitamins, but about the individual Vitamin B6 and B12 supplements, which can be 50 to 2000 times the recommended daily allowance.
Bob
A more readable story on the subject: http://www.cnn.com/2017/08/22/health/vitamin-b6-b12-lung-cancer-study/index.html...use of vitamin B6 and B12 from individual supplement sources, but not from multivitamins, was associated with a 30% to 40% increase in lung cancer risk among men. When the 10-year average supplement dose was evaluated, there was an almost two-fold increase in lung cancer risk among men in the highest categories of vitamin B6 and B12 compared with nonusers. For vitamin B6 and B12, the risk was even higher among men who were smoking at baseline.
http://ascopubs.org/doi/full/10.1200/JCO.2017.72.7735
This is not about multivitamins, but about the individual Vitamin B6 and B12 supplements, which can be 50 to 2000 times the recommended daily allowance.
Bob