"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. "Our data show that taking high doses of B6 and B12 over a very long period of time could contribute to lung cancer incidence in male smokers".
Scientists from the Arthur G. James Cancer Hospital and Richard J. Solove Research Institute at the University Comprehensive Cancer Center (OSUCCC) in Columbus, OH, joined forces with the Fred Hutchinson Cancer Research Center in Seattle, WA, and National Taiwan University in Taipei.
However, the study wasn't created to prove cause-and-effect between the vitamins and lung cancer; it only showed an association. For smokers takin B12, the risk was almost fourfold higher.
You also don't have to worry if you regularly eat foods high in vitamin B, like chickpeas, clams, tuna, salmon, or red meat. But some groups - such as older people and vegetarians - may be deficient and need supplements.
But naturally having higher levels is not the same as saying that taking lots of B6 or the popular energy vitamin B12 is protective.
The patients, aged 50 to 76, provided detailed information about their vitamin B usage over 10 years, including supplement dosages.
Lung cancer is the most commonly diagnosed cancer on a global basis (1.61 million diagnoses in 2008), as well as the most common cause of cancer-related death (with 1.38 million in the same year). These supplements have been broadly thought to reduce cancer risk. Further, the results of this study conflict with the results of previous studies, including a randomized control trial as well as two studies that measured vitamin B6 serum levels and demonstrated reduction in lung cancer risk.
Male smokers taking 20 milligrams of vitamin B-6 per day for 10 years were three times more likely to go on to develop lung cancer, while male smokers taking 55 micrograms of vitamin B-12 per day for 10 years were around four times more likely to develop the disease.
Prior studies created to assess the association between lung cancer risk and B vitamin intake have yielded inconsistent results.
Bottom line: While this study doesn't definitively prove that B supplements increase your lung cancer risk, it does provide enough evidence that guys who smoke or who have smoked in the past should reconsider taking high doses of it.
"That's marketing. That's not science", said Theodore Brasky, one of the study's authors, as reported by CNN.
"In contrast, most multivitamins include 100 percent of the U.S. Recommended Dietary Allowance, which is under 2 mg per day for B6 and 2.4 mcg per day for B12".