Using information from a large prospective study database designed to explore the relationship between dietary supplements and cancer, over 77,000 subjects were asked about their use of dietary supplements containing folate, vitamin B12 and B6 over a period of 10 years. Together with dietary intake assessed by a food frequency questionnaire, the participants were categorized according to zero, mild, moderate and high intake of B vitamins. Of course smoking history and other risk factors were taken into account and participants were followed for appearance of lung cancer. Those who developed lung cancer, mostly tended to be older, male, current smokers with chronic obstructive airways disease (COPD).

Higher intake of vitamin B6 and vitamin B12 (but not folate) for 10 years was found to nearly double the risk of lung cancer in men (but not women) and what is very telling is that the increase risk from B12 intake was seen with average daily intakes of > 55 mcg or about 23 times higher daily intake than the RDA (2.4 mcg/day). Many dietary supplements contain 500 mcg, 1,000 mcg or even 5,000 mcg - representing a 200 - 2,000-fold higher dose than the RDA. This is the first study to demonstrate that even a supplement dose of 50 - 55 mcg B12 when combined with normal dietary intake in an at risk population can be detrimental and reinforces the necessity for physiologic absorption of vitamin B12 with Intrinsic Factor and to avoid pharmacologic doses as seems to be standard in many current product offerings.