The alternative medicine community operates in a cloud (claims without hard evidence) based in part on the notion that whatever they do has to “improve the immune system.” There is little basis for this claim in improved outcomes, other than placebo effect.
A recent study in the Journal of AMA (JAMA. 2009;302:2119-2126) reports on a two placebo controlled studies from Norway in which patients received folic acid and vitamin B12.
The results indicate an excess of 3.5 new cases/1000/year and one excess case of lung cancer per 1,000 per year
Patients were followed for over three years. More patients receiving the vitamins were diagnosed with cancer (10% vs 8.4% P=.02) and more receiving the vitamins died (4% vs 2.9% P=.01). Another way of stating this, if we wanted to maximize the claim, would be that there was an almost 16% increase in cancer diagnoses and a 28% increase in death. Medicynical note: whenever you hear a percentage increase or decrease in something you can assume it overemphasizes the result.
About all that one can say about this study is that, regarding cancer prevention, B12 and folate offer no benefit and may even increase the risk.
Medicynical Note: One explanation of the finding is that in addition to whatever “positive” effects there are, B12 and folate also enhance the growth of cancer cells in some patients. One needs to be careful about therapeutic weapons that “enhance” something because they have double edges and enhance the wrong thing.