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Folic Acid and B12 Supplements Increase Cancer Risk

By November 21, 2009

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When it comes to cancer prevention, it's wise to steer clear of most supplements and instead focus on food. Numerous studies have suggested that many dietary supplements do not decrease cancer risk. Some supplements, in fact, actually may increase risk, raising concerns that supplements cause more harm than good for many people.

The latest study on this topic adds to these concerns with the finding that folic acid and vitamin B12 dietary supplements increase the risk of being diagnosed with cancer, of dying from cancer, and of dying from any cause.

By the Numbers

The study was a double-blind, placebo-controlled, randomized clinical trial in which nearly 7,000 adults in Norway were randomly selected to take one of the following:

  • 0.8 mg of folic acid + 0.4 mg of vitamin B12 + 40 mg vitamin B6 per day
  • 0.8 mg of folic acid + 0.4 mg of vitamin B12 per day
  • 40 mg vitamin B6 per day
  • placebo (no vitamins)

Double-blind means that neither the researchers nor the study participants knew who was taking which vitamins or the placebo. Randomized means that people were selected at random for each vitamin (or placebo) group. This type of study is considered "the gold standard" of research designs, because it is most likely to show results accurately, without errors that can happen with other study designs.

Study participants were followed for a median (similar to average) of approximately six and a half years (39 months of active study participation plus 38 months of post-study observation). The study showed that compared with people not receiving folic acid and vitamin B12, those who took these vitamins had:

  • 21% higher risk of being diagnosed with cancer (any type)
  • 38% higher risk of dying of cancer (any type)
  • 18% higher risk of dying of any cause

Taking vitamin B6 did not have any measurable effects (good or bad) on the health of the study participants.

Take Home Message

It is likely that most of the negative health effects shown in this study are related to folic acid, more than to vitamin B 12. Health experts have suspected for some time that folic acid may be a "double-edged" sword.

If people get plenty of folic acid early in life, including in the womb (in utero, during pregnancy) and through childhood, this appears to protect against later developing cancer. If, however, people get too much (excess) folic acid during adulthood, this seems to increase the overall risk of cancer, and of colon cancer in particular.

Also of note: This study showed harm from folic acid supplements in a country that does not fortify its food supply with folic acid. The United States does fortify the food supply with folic acid. This means that we already get a supplemental form of this nutrient in our diets in high amounts. This also means that the harms of taking additional folic acid supplements are more likely to occur in people who are living in the US.

The bottom line is that we should get our folic acid from foods naturally high in this nutrient, not from pills. No studies have ever shown that getting plenty of folic acid from food increases cancer risk. Plus, studies do show that eating folic acid-rich foods likely decreases cancer risk. The same is definitely not true of folic acid supplements.

Taking folic acid as a dietary supplement is not a good idea, unless advised to do so by your doctor, for a specific medical reason, such as pregnancy. Eating foods that are naturally rich in folic acid (not foods that are fortified) is a good idea for everyone, because these are the same foods that appear to reduce cancer risk when part of a healthy diet.

Healthy Eats

The best, natural food sources of folic acid include:

  • black-eyed peas (beans)
  • pinto beans
  • chickpeas (garbanzo beans)
  • spinach
  • okra
  • black beans, navy beans, and other beans
  • asparagus
  • collard greens
  • kale
  • chard
  • other green leafy vegetables
  • broccoli
  • artichokes
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