HOME
Folic acid and colon cancer
Editor's Letter Diana Swift
Editor-in-Chief
editor@canadian-health.ca
The law of unintended results. Collateral damage.
These are factors in health, just as in war and economics.
This June, a U.S. study reported that older women taking calcium and vitamin D had a lower risk of cancer than their unsupplemented peers. Some researchers speculated that current guidelines for minimal exposure to the sun and heavy use of sunscreens might be interfering with our natural production of vitamin D, a cancer-fighting nutrient made by the body when skin is exposed to solar UVB rays. One commentator implied that in trying to prevent the relatively few deaths from sun-induced skin-cancer we might be boosting mortality from bigger killers such as colorectal and breast malignancies. Photo : Susan Ashukian
Now folic acid fortification has come under scrutiny. Writing in the journal Cancer Epidemiology Biomarkers & Prevention, scientists at Tufts University in Boston raised the question whether increased intake of the man-made form of this water-soluble B vitamin — in fortified foods and supplements — might be contributing to an upward tick in U.S. and Canadian colon cancer cases. After a decade of decline, these began to rise slightly in the late 1990s, by four to six more per year than expected.
In 1998, the U.S. and Canada mandated the addition of folic acid to grain-based products such as white flour and pasta. This measure aimed to reduce neural-tube defects (NTDs) in babies. NTDs are malformations of the structure becomes the spinal column.
And reduce NTDs it did. In 1993, NTDs in Canada stood at 1.58 per 1,000 births; by 2002, that number had fallen to 0.86 per 1,000 births, according to a study led by Dr. Philippe de Wals of Laval University in Quebec City. The nutrient has also been linked to a lower risk of other birth defects such as cleft palate and a reduced risk of cardiovascular disease.
This B vitamin is essential for the normal division and replication of healthy cells, but the rampantly dividing cells of cancer use it to replicate, too. In fact, antifolate drugs such as methotrexate are among the oldest forms of cancer chemotherapy. So while high intakes of folate — the version that occurs naturally in unfortified foods — have been associated with a lower risk of colon cancer, a U.S. study reported that daily doses of folic acid, the man-made version, did not reduce precancerous colon polyps and might even increase the risk of some types of colorectal tumours.
According to Dr. Joel Mason, who led the Tufts research, excess intake of folic acid may make older people more susceptible to colon cancer. As many as half of people over age 50 already harbour precancerous colon polyps, and excess folic acid might put cell replication into overdrive and spur progression to cancer. Mason notes that older men and women may need to reconsider the practice of taking extra folic acid in multivitamin or B-complex tablets, or may need to ask for formulas offering fewer than the 400 micrograms many contain.
Mason also says that the synthetic version may not be absorbed as well. The folic acid left over in the circulation might have detrimental effects, as it is not a natural form of the vitamin. While food fortification has undeniably reduced NDTs in babies, Masons calls for further study of its impact on the population as a whole.
The daily upper tolerable limit for folic acid is set at 1,000 micrograms, and folate absorbed from food is generally considered safe. Foods rich in this vitamin include fortified grain products, citrus fruit, lentils and green vegetables such as asparagus, bok choy and spinach. If you like enriched bread and pasta, legumes, fruit and greens, your diet can easily supply the 400 micrograms recommended for most adults. A single serving of a fortified cereal with milk can deliver 42% of your daily requirement, one enriched hamburger bun 35%. So an additional 400 micrograms of the synthetic form could be too much for some people.
What this debate says to me is that the biological effects of nutrients are highly complex, and good health policies aimed at one group may involve unforeseen consequences, trade-offs and downsides for others.
Reference
Mason JB, Dickstein A, Jacques PF, Haggarty P, Selhub J, Dallal G, Rosenberg IH. A temporal association between folic acid fortification and an increase in colorectal cancer rates may be illuminating important biological principles: a hypothesis. Cancer Epidemiol Biomarkers Prev. 2007 Jul;16(7):1325-9
Related Articles
