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Can Folic Acid Be Harmful?

New research on the human metabolism of folic acid suggests natural sources of folate are preferable

November 8, 2010 |
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Folic acid supplements, which are recommended for all women of child-bearing age to prevent birth defects. Harmful, harmless, or helpful? In other words vitamin and panacea or, genetic time-bomb? I do not recommend folic acid supplements; I recommend folate, from the same word root as foliage, found in dark green leafy vegetables and legumes.
But everybody knows no one eats greens and beans every day, so the government started fortifying our food supply with folic acid in 1998. Folic acid, though, is not the same thing as folate, but it’s cheaper and more stable in pill form, so that’s why they use it instead. In fact folic acid is a synthetic chemical not found in nature at all—but, studies on rats found that there’s an enzyme in the liver that basically changes it into the natural form.
Studies keep coming out, though, linking folic acid supplementation with diseases like breast cancer and colon cancer. So yes, it lowers the risk of birth defects, but may raise our risk of cancer. But wait a second, spinach doesn’t raise our risk of cancer. Beans and greens lower the risk of both birth defects and cancer. It was a big mystery until last year, when scientists figured out: we’re not rats.
It’s hard to study human livers, because people tend to need them, but sometimes an organ donor dies and there’s no one to take the liver, and so scientists were finally able to see if what happens in rat livers happens in human livers. And it turns out that the enzyme that converts folic acid in pills into something our body can actually use, is 50 times less active than in rats. Less than 2% of the activity we thought it had, based on the animal studies. So because our enzyme is “extremely slow,” people who take folic acid pills have lots of this synthetic folic acid circulating in their bodies and that’s what we think may be behind the elevated cancer risk. Whereas beans and greens every day offer the best of both worlds.

To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring watch the above video. This is just an approximation of the audio contributed by veganmontreal.

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Dr. Michael Greger

Doctor's Note

Please feel free to post any ask-the-doctor type questions here in the comments section and I’d be happy to try to answer them. And check out the other videos on folate. If you're worried about the gassiness of beans as a source of folate, check out my blogpost Clearing the Air. Also, there are 1,686 other subjects covered in the rest of my videos--please feel free to explore them as well!

For some context, please check out my associated blog posts: Multivitamins and MortalityBreast Cancer and Diet, and Soymilk: shake it up!

If you haven't yet, you can subscribe to my videos for free by clicking here.

  • Michael Greger M.D.

    Please feel free to post any ask-the-doctor type questions here in the comments section and I’d be happy to try to answer them. And check out the other videos on folate. If you’re worried about the gassiness of beans as a source of folate, check out my blogpost Clearing the Air. Also, there are 1,449 other subjects covered in the rest of my videos–please feel free to explore them as well!

  • Brandon Becker

    What about folic acid supplements for vegans during pregnancy? Healthy vegan diets are high in folate so it seems possible and certainly preferable to get this nutrient from food rather than supplements.

    • Toxins

      The fact that folic acid is attributed to the diseases mentioned in the video makes taking it as a supplement out of the question in my opinion. Its similar to taking a beta carotene supplement, what they have done is isolated a single carotenoid and super concentrated it in a pill. The prenatal supplements are truly not necessary, especially if one is eating as health a a plant based eater.

      Check our Dr. Greger’s video of the dangers of Iron during pregnancy and the vitamin supplements worth taking.

  • NickyC

    Hi Brandon,
    Correct, a vegan diet high in greens, such as spinach, and legumes, like black beans, will be an excellent source of folate during pregnancy.
    Please note, however, that a vegan diet is often deficient in iodine, which can pose problems during pregnancy. Please check out this video for more information:

    • brok

      Its vitamin b12 you will lack, but require

  • YD

    Should we avoid folic acid in supplements completely? I’m looking into B-complex supplements and almost all of them contain 1 mg of folic acid. Thanks for all the awesome videos!

    • Toxins

      The study measured folic acid at 1 mg or higher. 1 mg is considered the upper tolerable intake of folic acid. They note that .4 mg of folic acid in individuals gets metabolized to folate but higher than that and we get unmetabolized circulating FA which is harmful. If you are eating a well balanced plant based diet the only supplement you would need is vitamin b12. A B-complex is not necessary.

      • YD

        Thank you so much for the reply! Yeah I was also wondering if B-complex was necessary, I heard from some sources that your body really wants all the B vitamins to be taken together. But Dr Greger seems to recommend B 12 supplement only.

        • Toxins

          It is true that almost all whole plant foods contain a mix of the b vitamins, but just because they lack b12 doesn’t mean that the other b vitamins are ineffectively used, nor should we have any reason to believe so.

          • YD

            I guess when I really think about it, it makes sense that since we can get the rest of the B vitamins from a plant-based diet, the only supplement we need is B 12. Thanks again for your reply :)

  • Michael Greger M.D.

    For some context, please check out my associated blog post Multivitamins and Mortality!

  • Lachicavegana Comefrutas

    There are food based vitamins such as MegaFood, which offer folate in the normal food form, from broccoli. 40 percent of population has MTHFR genetic mutations which affect the absorption of folate, to varying degrees. The synthetic folic acid is probably more harmful to these people and on top of that, they may need food based supplements-depending on the health of their gut and which mutation they have. It is insane that folic acid is added to everything.

  • Michelle Mercer

    I was on 5mg folic acid daily to offset harmful effects of methotrexate (for Rheumatoid Arthritis) I’m currently off the mtx but has the 5mg a day possibly done my body harm? I know the mtx probably has! :(

  • Toni Gutierrez

    Is this supplement ok? It contains Folate (5-Methyltetrahydrofolic Acid), not Folic acid:

    • chicovegano

      5 MTHF is the folate that is actually used in the folate cycle to to make B12. If your folate is not able to be converted to 5-MTHF because of an enzyme deficiency (MTHF reductase) then this is the one that will keep your B12 levels up, your homocysteine levels down and keep your methylation happy. Folic Acid (provided by law in all enriched products) is not found in nature but is quite shelf stable in foods, and requires several more steps to turn into 5-MTHF. We are provided so much in our over consumption of enriched foods (think anything with flour that is not 100% whole wheat) that the build up of Folic Acid can be toxic and cause its own problems. And as chicavegana comefrutes commented above, a large segment of the population has the defective MTHF reductase enzyme which greatly puts them at risk.

      • brok

        Dude, you are so wrong. Go back to college

  • eva101

    What is your opinion about L-methylfolate .

  • PM

    Hi Dr. Greger: I was wondering about Perfect Prenatal by New Chapter Organics as is is a whole foods vitamin which includes “folate” not “folic acid”. Also, I am wondering about Seeking Health L-5 MTHF 1000 which claims to provide only folate as “metafolin” for people with the MTHR issue. In general, are vitamins containing “folate” no “folic acid” ok?

    • Tommasina

      I think Dr. Greger would stick to his assertion that getting vitamins from whole foods and not pills, will serve our bodies better. Beans and greens are great, affordable sources of folate. :) Hope that helps.

  • Methyl Kiki

    Dr. Greger, you need a video on MTHFR defects. Some people do process folic acid, but 40% of the population have an MTHFR defect that causes them not to process folic acid into folate. So your recommendation that everyone eat beans and greens is right on target; however, people with MTHFR defects should take a multi and B-complex containing the natural form of folate. In fact, there are studies that link pregnant women who have this defect and take prenatal vitamins containing folic acid are at much high risk for premenopausal breast cancer. That’s 40% of women! (MTHFR polymorphisms, dietary folate intake, and
    breast cancer risk: results from the Shanghai Breast Cancer Study. Shrubsole MJ1, Gao YT, Cai Q, Shu XO, Dai Q, Hébert JR, Jin F, Zheng W.

    Since my entire family has one or two MTHFR defects, I’ve been reading more and more and am astounded by the statistics, some of which you state that are probably related to MTHFR people ingesting folic acid-fortified foods and increasing incidences of various types of cancer, but it’s more than that. It probably has a hand in every western degenerative disease. As you know, methylation is essential for the proper function of most body systems and cellular processes. It is also needed to support glutathione production which neutralizes free radicals, helps the body process toxins and supports proper DNA synthesis and repair and other metabolic processes. It is required for the creation of every cell in your body. Consequently, it is easy to see how this mutation could have a role in many conditions and diseases. And while I agree that if one is a vegetarian or vegan and eats beans and greens and does not take folic acid or eat fortified foods, their folate status will likely be good enough to not have problems with MTHFR; this is unfortunately not the case for the majority. Please do a video on MTHFR. 40% of the population is a lot of people. Get this, 98% of autistic people have this defect. No wonder they may have trouble processing toxins. Great site. Love the information. You do a great service to the many seekers of nutritional and medical knowledge! Many thanks!