B vitamins may raise risk of lung cancer in men who smoke

In the journals

Smoking causes lung cancer — no surprise there. But a new study found that high dosages of vitamin B6 or B12 supplements were associated with three to four times the lung cancer risk in male smokers compared with smokers who did not take the supplements. The results were published in the Aug. 22, 2017, Journal of Clinical Oncology.

Researchers examined information from more than 44,000 men ages 50 to 76. At enrollment, the men reported on their smoking history and their B vitamin supplement use over the previous 10 years. In the study, high intake of B vitamin was classified as 20 milligrams (mg) of B6 per day or 55 micrograms (mcg) of B12. (The recommended daily intakes for men ages 51 and older are 1.7 mg for B6 and 2.4 mcg for B12.)

B vitamins help strengthen the immune system, according to the researchers, so it is not clear why high levels of supplemental B vitamins would increase rather than decrease smokers' lung cancer risk. They speculated that the B vitamins might feed small, undetected tumors and make them grow faster.

B vitamins aside, not smoking remains the most important way to prevent lung cancer. In fact, the researchers also found that men who quit smoking for at least 10 years before the study and also took high dosages of the B vitamins did not have a higher risk of lung cancer. In fact, their risk was equal to that of men who had never smoked.