This new study from Seattle's Fred Hutchinson Cancer Research Center has added more weight to folic acid (the synthetic form of folate) supplementation may increase the risk of certain cancers--this time colorectal cancer.
This finding came from using data from the Women's Health Initiative Observational Study, which included over 88,000 postmenopausal women who were studied between 1993-1998.
In the mid-1990s, the United States mandated folic acid fortification in certain foods (i.e. processed grain products) to reduce the incidence of neural tube defects (like spina bifida). Most of this fortification used (and continues to use) the synthetic folic acid --rather than natural folates--since folic acid has much better bioavailability.
Since this was an epidemiological study, we can only observe correlations with nutrient analysis, and when the researchers looked at folic acid consumption, they found that those in the top 25% of folic acid consumption had highest incidence of colorectal cancer.
Although it's too early to say with certainty if folic acid causes colorectal cancer, based on other studies that show folate (the naturally-present form found in food) reduces cancer risk...well, you can follow the logic here. Further, other research has found that high doses of folic acid can promote the growth of existing tumours and increase cancer risk in general.
So if you're looking to meet your folate requirements, eat a diet high in natural, unprocessed foods, including leafy green vegetables. If you want to supplement, choose a product that contains L-methyl-folate (A.K.A. 5-methyltetrahydrofolate, or 5-MTHF), which is the biologically active, co-enzyme form of folate.
Source: B vitamin intakes and incidence of colorectal cancer: results from the Women's Health Initiative Observational Study cohort
And end with some fun, here's another video (similar to the dog video I posted a couple years ago)...
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