I’m going to couple my last post (Taking Vitamin E Supplements Increases The Risk For Prostate Cancer) with this post about the link between folic acid and cancer. Because people are also still taking folic acid supplements in this country (take a look at your multivitamin), even though this combined analysis of 2 large, randomized, double-blind, placebo-controlled trials (the gold standard of scientific investigation):

Cancer Incidence And Mortality After Treatment With Folic Acid And Vitamin B12, Journal of the American Medical Association, November 2009

… found:

“Conclusion: Treatment with folic acid plus vitamin B12 was associated with increased cancer outcomes and all-cause mortality in patients with ischemic heart disease in Norway, where there is no folic acid fortification of foods.”

There was a 21% increased risk for getting cancer and a 38% increased risk of dying from cancer. Lung cancers dominated. Patients who experienced increased risk were taking 800 micrograms/day (mcg/d) of folic acid.¹ (They also took 400 mcg/d of vitamin B12 and/or 40 mg/d of vitamin B6.)

The recommended allowance (or DRI: Dietary Reference Intake) for folic acid in this country is 400 mcg/d. So they were taking twice the DRI. Yet they fell short of the tolerable upper intake of 1000 mcg/d.

In our body, folate is used in DNA replication; it’s needed for cell growth and repair. Cancer cells also use it for growth. “High doses of folic acid may speed cell division and increase tumor progression in preneoplastic lesions.”

Two items of note:

1. Participants in these studies lived in Norway where there is no fortification of foods with folic acid. The US embarked on a mandatory fortification program in 1998 – flour and grain products here contain added folic acid. That’s in addition to the folic acid added to our breakfast cereals, often 400 mcg/serving. (A bowl of cereal and a typical vitamin pill can easily put you at 800 mcg. Eat anything made with folic-acid-fortified-flour and you’ll surpass their intake.)
2. One mechanism put forth for the increased cancer rates was reduced activity of our immune system’s natural killer cells in the presence of high levels of folic acid.² Coincidentally, high intakes of omega-3 (about 1 gram/day) were also seen to reduce the amount and activity of natural killer cells.

Taking vitamins is not as innocent as supplement manufacturers lead us to believe. But people still think a vitamin pill is harmless.

¹ Folate found naturally in food hasn’t been shown to be harmful. Green leafy vegetables are a great source.
² Unmetabolized Folic Acid in Plasma Is Associated with Reduced Natural Killer Cell Cytotoxicity among Postmenopausal Women, Journal of Nutrition, 2006