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High Doses of Folic Acid May Increase Breast Cancer Risk


Folic acid is a B-vitamin that helps the body make new cells. While every needs the vitamin for optimal health, too much may actually increase the risk of disease, including breast cancer in women.

Researchers with St. Michael’s Hospital in Canada, led by Dr. Young-In Kim, studied the effects of folic acid in laboratory rats and found that when given doses two-and-a-half to five times the daily requirement, supplements of the B-vitamin promoted the growth of existing pre-cancerous or cancerous cells in the mammary glands.

Folic acid supplementation was also associated with an increased expression of BAX, PARP, and HER2, genes associated with an increased risk of cancer.

Though the latest study was carried out in rats, the researchers say that their findings "suggest that there is sufficient cause for concern about the potentially deleterious effect of folic acid supplementation on breast cancer progression."

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Today, many foods are fortified with folic acid with the goal to reduce the incidence of neural tube defects, such as spina bifida, in newborns. Since 1998, the US and Canadian governments have commanded the mandatory fortification of foods such as white flour, enriched pasta, and cornmeal products.

Fortification has been successful. Folic Acid can prevent major birth defects of baby’s spine and brain by 50-70%.

However, in addition to food sources, about 30-40% of North Americans also take dietary supplements for potential benefits, which the researchers note are currently unproven. The researchers note that cancer survivors in particular are a group that uses vitamins and supplements more than the general population.

The Office of Dietary Supplements, part of the National Institutes of Health, has set the recommended daily level of folate intake at 400 micrograms (mcg) for men and women over 19 years of age. Natural sources of folate include leafy greens (such as spinach), broccoli, egg yolks, lentils and oranges.

Journal Reference:
Young-In Kim et al. Folic Acid Supplementation Promotes Mammary Tumor Progression in a Rat Model. PLoS One. Published: January 21, 2014 DOI: 10.1371/journal.pone.0084635

Additional Resource:
Centers for Disease Control and Prevention