And vitamin B6 and B12 supplements didn't seem to affect risk in women. If they also smoked, their risk of cancer was up to four times higher.
Vitamins B6 and B12 have been touted for their potential to accelerate metabolism and increase energy. That's important because, at the very least, this correlation appears to suggest that taking mega-doses of vitamins to improve general health (including for cancer risk) isn't an effective strategy and certainly doesn't reverse the effects of smoking.
"I think it's hard to say" why these studies contradict each other, said Elizabeth Kantor, an epidemiologist at Memorial Sloan Kettering Cancer Center who has studied dietary supplements and cancer risk.
More than 800 of these people were found to have invasive lung cancers over the study's course, and the risk seemed to be especially associated with men who took discrete supplements with vitamin B6 or B12.
And a trade organization representing the vitamin industry cautioned against reading too much into the study. The participants were recruited from 2000 to 2002, and answered questions about their vitamin use over the previous 10 years.
The researchers acknowledged limitations to their study, including the lack of information about cohort members' environmental or lung cancer risk factors, as well as lack of serum B-vitamin measurements to assess prevalence of suboptimal intake or to complement their findings from self-reported intake. Or it may be that lung cancer itself raises levels of these vitamins in the body.
"That's marketing. That's not science", he said. People should really ask themselves if they need over 1,200 times the RDA (recommended daily allowance) of a substance.
B vitamins are involved in this pathway, but, at higher doses, the pathway may be compromised, promoting carcinogenesis. There also has been speculation that these vitamins may reduce cancer risk.
He went on to explain that the "use of combustible tobacco is a far more important factor in lung cancer development in both men and women".
Still, Brennan added that "there is clearly no evidence that these vitamins have any substantial protective effect".
Dr. Eric Bernicker, a thoracic oncologist with Houston Methodist Hospital, agreed with that advice and said the study points to a higher risk of lung cancer from higher doses. "As in much of nutrition, the story is more complicated than that", Bernicker said. A high dose of B6 is considered 20 milligrams, but supplements come in doses of up to 500 milligrams. Among other things, it required participants to remember what they consumed over 10 years. The study was headed up by Theodore Brasky, Ph.D. - from the OSUCCC - and their results are published this week in the Journal of Clinical Oncology.