"Like most nutrients, there appears to be an ideal range forA new study in JAMA this week is reporting an increased cancer risk among those who took folic acid supplements:
omega-3 fatty acidsfolate in the body, above and below which an individual can experience poor health."
Cancer Incidence and Mortality After Treatment With Folic Acid and Vitamin B12, Journal of the American Medical Association, November 2009
The risk was not high (21% increased risk for getting cancer, 38% increased risk of dying from cancer) but it was statistically significant. 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.
Two items of note:
- Participants in this combined analysis 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.)
- 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.
2 Unmetabolized Folic Acid in Plasma Is Associated with Reduced Natural Killer Cell Cytotoxicity among Postmenopausal Women, Journal of Nutrition, 2006