Folic Acid (Vitamin B9) and Breast Cancer
Updated on December 9, 2025
Key takeaways
There’s evidence that higher levels of dietary folate may lower the risk of breast cancer in some people, but it’s not clear if folic acid supplements have the same effect.
Pregnant people who take folic acid supplements before and during pregnancy are less likely to have children with neural tube defects.
Folic acid supplements are generally safe for most people.
Folate (vitamin B9) is found naturally in food, and folic acid is an artificial form of folate that’s used in supplements. It’s most commonly taken by people who are pregnant (to reduce the risk of neural defects in newborns) and people who don’t get enough folate from their diet.
You may have heard another form of vitamin B9 (called leucovorin) come up in the news lately, as some people claim it can help people with autism.
Some people believe folate may decrease the risk of breast cancer, but the research is mixed.
What the research shows
Breast cancer risk
A 2014 report found that higher folate intake may lower the risk of breast cancer in women with higher levels of alcohol intake, but not for those with lower alcohol intake. (Alcohol makes it hard for the body to absorb folate from food or supplements.) Another study showed that dietary folate intake was associated with a lower risk of breast cancer in people who did not drink alcohol regularly. Breast cancer risk was even lower in people with a higher dietary intake of methionine, vitamin B12, and vitamin B6. But these studies focused on dietary folate, not folic acid supplements.
One 2008 study looked at folic acid supplements — in combination with vitamin B6 and B12 — and found that the supplements had no significant effect on breast cancer risk.
Since the results of these studies have been mixed, it’s not clear whether folate affects breast cancer risk in a meaningful way.
Risk of other cancers
Some studies in animals and people have suggested that taking high doses of folic acid may increase cancer risk and boost tumor growth.
Other studies have found
not getting enough dietary folate may increase the risk of esophageal cancer
eating a diet high in folate may decrease the risk of pancreatic cancer in men who smoke
folic acid may lower the risk of colorectal cancer (CRC) in people who have a family history of CRC or are at high risk of the disease
eating a diet high in folate had no effect on the risk of colon cancer in women or people who drink alcohol frequently
More research is needed to understand the links between folate, folic acid, and cancer risk.
Pregnancy
A 2023 report by the U.S. Preventive Services Task Force concluded that pregnant people who took folic acid supplements before and during pregnancy were less likely to have children with neural tube defects.
Are folate and folic acid the same?
Folate and folic acid are both forms of vitamin B9. However, folate is found naturally in foods, whereas folic acid is a synthetic form of the vitamin used in supplements and fortified foods.
Because it can be difficult for pregnant people — or people with folate-deficiency anemia — to get enough folate through diet alone, many take folic acid supplements.
Folic acid can be found in B-complex supplements, prenatal vitamins, and in a standalone supplement. You may see supplements referred to as either “folate” or “folic acid.”
Sources of folate
High amounts of folate are found in a variety of foods, including:
beef liver
dark leafy greens
legumes and beans (like kidney beans, edamame, and black eyed peas)
cruciferous vegetables, like broccoli
avocado
asparagus
some grains, like rice and wheat
Other foods, like chicken breast, ground beef, milk, and halibut, contain small amounts of folate. See the USDA’s comprehensive list of dietary folate sources (PDF).
Risks and side effects of folic acid
Folic acid in fortified foods and supplements in doses of less than 1 milligram per day is considered safe. Doses of more than 5 milligrams per day can cause abdominal cramps and diarrhea. Large intakes of folic acid can also mask a vitamin B12 deficiency.
What this means for you
If you’re pregnant or trying to get pregnant, taking a folic acid supplement or a prenatal vitamin that includes folic acid can help prevent birth defects.
It remains unclear how folic acid affects breast cancer risk — and the risks of other cancers. Be sure to talk to your doctor before taking a folic acid supplement.