Do Folic Acid Supplements Cause Cancer?

Folic acid is known to prevent certain birth defects, such as neural tube defects, spina bifida and cleft palate. It’s been widely recommended as a supplement and used as a fortification in flours and grain products. Aside from these benefits, research also shows a concerning link between folic acid supplements and cancer.

Folic Acid vs. Folate

The terms folic acid and folate are often used interchangeably, but they’re not the same thing. Folate is an essential B-vitamin that naturally occurs in food, also called vitamin B9 or folacin. It is required for cell division, DNA repair, immune function, energy production and cognitive health.

When folate is isolated from food, it breaks down quickly and is not useful as a supplement. But it can be transformed through an oxidation process into folic acid, a synthetic compound which is more stable and has a long shelf life. This is the folic acid that’s used in dietary supplements and food fortifications.

Human cells cannot metabolize a folic acid molecule. Instead, the liver transforms folic acid back into its folate form, which can then be used by the body. This is how folic acid supplements can be absorbed and help prevent birth defects.

The Problem with Folic Acid

Researchers have looked into the effects of synthetic folic acid used in supplements and food fortification. Various international studies have found many disturbing results linked to folic acid use, including:

  • An increase in lung cancers.
  • An increased risk of breast cancer in postmenopausal women.
  • An increased risk of prostate cancer with daily supplementation of 1 mg of folic acid.
  • Women who take high doses of folate throughout pregnancy may be more likely to die from breast cancer later in life than women taking no folate.
  • In the U.S., Canada, and Chile, colorectal cancer rates have climbed since mandatory fortification of food with folic acid was introduced.
  • High intake of folic acid is also associated with cognitive decline in the elderly.

Most of these studies used the recommended daily intake of folic acid or more, which is 400 micrograms per day. There appeared to be a greater link to disease with higher dosages.

It’s unclear exactly why folic acid may increase these health risks, although some of the studies found high levels of un-metabolized folic acid in the blood. This would suggest some kind of toxic effect from excess supplementation, as opposed to consumption of folate in foods, which would be metabolized and absorbed properly.

Also, our body’s ability to transform folic acid into folate decreases as we age, so any supplementation may remain in the bloodstream even longer. This may be part of the link to cognitive decline in the elderly.

Current Recommendations

1. Eat foods rich in folate. In contrast to folic acid, many studies have shown a diet rich in folate-containing foods protects against cancer and cognitive decline. Good options include dark green vegetables, such as leafy greens, broccoli or peas, as well as oranges, lentils and beans, grains and meats.

2. Avoid folic acid supplements and fortified foods. Some countries, such as the United States and Canada, have mandated certain refined flours and grain products to be fortified with folic acid. If a product is fortified, folic acid will be listed in the ingredients. The same is true for vitamins, watch out for folic acid on the label. Some vitamin producers are aware of the risks of folic acid and are starting to use natural sources of folate instead. The natural forms will be listed as folate, “5-methyltetrahydrofolate,” or “5-formyltetrahydrofolate” on the label.

3. Get a blood test to check your folate levels. Especially if you’re planning a pregnancy, or if you’re concerned about your current folate levels, it’s recommended to get a red blood cell folate analysis. This can measure the amount of folate that was present when your red blood cells were created, up to 4 months earlier, which is a good sign of your current folate levels. Check with your doctor about how to get a test.

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58 comments

Siyus Copetallus
Siyus Copetallus2 years ago

Thank you for sharing.

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Quanta Kiran
Quanta Kiran2 years ago

i just started taking folic acid!

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Natasha Salgado
Past Member 2 years ago

Wouldn't be surprised at all. Don't trust any supplements. thanks

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Heidi Aubrey
Heidi Aubrey2 years ago

Just remember, supplement companies are NOT the least interested in your health.

They simply look at the population and see where a lot of money is being spent, then develop a product for that market at the least possible cost.



If you ever see a multiple vitamin supplement using iron oxide as its source for iron-that says it all for that company. Iron oxide is the absolute cheapest and most poorly absorbed form of iron there is. You can be sure the entire formulation is equally as cheap.

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Carole R.
Carole R2 years ago

I am beginning to think supplements, in general ,are not good.

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Jim Ven
Jim Ven2 years ago

thanks for the article.

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Elena Poensgen
Elena Poensgen2 years ago

Thank you

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Elena Poensgen
Elena Poensgen2 years ago

Thank you

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Carolyn F.
Carolyn F.2 years ago

Oh great! I take folic acid with my rheumatoid arthritis medicine on a daily basis and so do many others. When will this medicine as poison scandal stop? Do physicians even care about the general health of their patients? I give up!

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Jamie Judd
Jamie Judd2 years ago

I actually have a friend who insists on taking folic acid supplements whenever he & his wife were trying to conceive. He insists it raises a mans sperm count. I honestly don't know how true that is & after reading this, I'm not so sure the benefits outweigh the risks.

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